高圧下で合成された充填スクッテルダイト化合物
Smy(Fe1-xNix)4Sb12 の熱電特性
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言語: English
出版者:
公開日: 2020-12-15
キーワード (Ja):
キーワード (En):作成者: フュアンヨッド, アトチャリヤ
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URL

https://doi.org/10.15118/00010337

DISSERTATIONTHERMOELECTRIC PROPERTIES OF FILLED
SKUTTERUDITE COMPOUNDS Sm y (Fe 1-xNi x ) 4 Sb 12
PREPARED UNDER HIGH PRESSUREMURORAN INSTITUTE OF TECHNOLOGY
Doctor of Engineering
Course of Advanced Information and Electronic Engineering
Physics of Strongly Correlated Electron Systems Laboratory
Admission in 2017
Student ID number 17096506

ATCHARIYA PHUANGYOD
Submission in 2020

THERMOELECTRIC PROPERTIES OF FILLED
SKUTTERUDITE COMPOUNDS Sm y (Fe 1-x Ni x ) 4 Sb 12
PREPARED UNDER HIGH PRESSURE
byAtchariya Phuangyod

A dissertation submitted in partial fulfillment of the requirements for the degreeof Doctor of Engineering

Examination Committee:

Prof. Sekine Chihiro

Nationality:

Thai

Previous Degree:

Bachelor of Electrical Engineering
Chiang Mai University, Thailand
Master of Energy Engineering
Chiang Mai University, Thailand

Scholarship Donor:

Japan Student Services Organization (JASSO)
Muroran Institute of technology (MuIT)
Scholarship

Muroran Institute of Technology
Japan

September 2020

ACKNOWLEGEMENT

The author wishes to express her profound gratitude to her advisor, Prof.
Sekine Chihiro for her supporting study, helping with living in a foreign country,
friendly discussions, helps to reduce study stress, and all valuable efforts for theaccomplishment of her study. She thanks also go to Assoc. Prof. Kawamura
Yukihiro, Dr. Junichi Hayashi, and her laboratory members for kindly teach her
the experiment, and supporting study.
The sincere thanks also go to express her master’s graduate advisor,
Asst.Prof. Wongkot Wongsapai, and Assoc.Prof. Chatchawan Chaichana, Chiang
Mai University, Thailand for encouragement and advice.
The author wishes to special thanks to her beloved family, Ms. Sirirat
Phuangyod, Mr. Samrite Phuangyod, Mr. Kha Kuppheng, and Miss Sujitra
Kuppheng for the support and encouragement of the author always, and friends
whom the author cannot mention name all for making laughter, creating fun,helps relieve stress, always support the author.
Lastly, sincerely thank you to the Muroran Institute of Technology forproviding the opportunity to study and to provide the author with a worthwhile
experience that is nowhere else.
This study is intended for the self-development of the author. Giving theauthor the knowledge, ability, and living with others, patience, diligence. The
author is extremely ecstatic, and very grateful to these precious experiences.

iiTopic:Thermoelectric properties of filled skutterudite compounds
Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared under high-pressure

Author:Atchariya Phuangyod

Degree:Doctor of Engineering

Course:Advanced Information and Electronic Engineering

Advisor:
Professor Sekine Chihiro________________________________________________________________

ABSTRACT
Filled skutterudite compounds are one type of TE that suitable for the useof advanced TE potentials of applications. It has been studied as one of the mostpromising TE based on Phonon Glass Electron Crystal (PGEC) concept implying,these have a phonon of crystal that is “glass-like” behavior, lattice thermal
conductivity like amorphous material but an electronic structure like solid
crystalline.
In this study, thermoelectric properties of p-type and n-type filled
skutterudites Sm y (Fe 1-x Ni x ) 4 Sb 12 samples as the nominal composition of 0 ≤ Ni
≤ 0.56 and 0.1 ≤ Sm ≤ 1.2 prepared by the high-pressure technique at pressure up
to 2 GPa. The samples were characterized by X-ray diffraction (XRD). The actual
element was estimated by a scanning electron microscopy (SEM) with an energydispersive X-ray spectrometry (EDX), and the electron probe microanalyzer(EPMA), respectively. The electrical resistivity was estimated by the Cryostat
vacuum system with a standard dc four-probe method, the thermal conductivity,
the Seebeck coefficient measurements, and Hall effect were performed by aphysical property measurement system (Quantum Design PPMS option TTO) at
temperature range 2 K to 300 K. The Seebeck coefficient of samples exhibitedthe p-type and n-type skutterudite depended on tuning Sm-filled, and Fe/Ni
content.

The

highest

ZT

value

of

0.167(7)isachieved

for

Sm 0.09 (Fe 0.61 Ni 0.39 ) 4 Sb 12.5 at room temperature.

iii

CONTENTS

Chapter

Title

Page

Acknowledgement
Abstract
Table of Contents
List of Figures
List of Tables
List of Abbreviation

ii
iii
iv
vi
ix
x

1

Introduction
1.1 Introduction
1.2 Motivation
1.3 References

1
1
4
6

2

Theories and literature reviews
2.1 Thermoelectric effect
2.2 Thermoelectric performance
2.2.1 Thermoelectric parameters2.2.2 Transport parameters2.2.3 Hall Coefﬁcient, Carrier and Mobility
concentration
2.3 Phonon glass-electron crystal (PGEC)
2.3.1 Skutterudites
2.3.2 p-type and n-type filled skutterudite
compounds
2.4 High-pressure synthesis technique
2.5 References

7
7
9
12
14
15

Experimental methods
3.1 The high-pressure synthesis (HPS)
3.2 Powder X-ray diffraction: XRD
3.3 Scanning electron microscope: SEM & EDX
3.4 Electron Probe Microanalyzer (EPMA)
3.5 Cryostat vacuum system

28
28
31
34
37
43

3

17
18
20
24
26

iv

Chapter

Title
3.6

3.7

Page
Physical property measurement system: PPMS
3.6.1 TTO measurement
3.6.2 Hall effect
References

45
46
50
55

4

Results
4.1 Sample characterization
4.2 Thermoelectric properties
4.3 Summary
4.4 References

56
56
67
80
81

5

Conclusion
5.1 Conclusion
5.2 References

83
83
85

Appendix A

Journals

87v

LIST OF FIGURES

Figure

Title

Page

1.1.1.

Thermal energy transfer from p-type to n-typesemiconductor materials.
Thermoelectric modules (TEM) and applications.
The Seebeck effect.
The electrical conductivity, Seebeck coefﬁcient, power
factor, and thermal conductivity depend on carrier
concentration.
Performance of p- and n-type thermoelectric materials.
The occurrence of the hall effect.
Unfilled and filled-skutterudite structure.
The basic configuration of TEM (a) basic unit, and (b)realistic model.
The p/n crossover of direct reaction of the elements at
1223 K, followed by quenching and subsequent sintering
at 873 K.
p-type of Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared by Sm y (Fe 1x Ni x ) 4 Sb 12 prepared by A quick melting, an annealing.
(SKUT series: A quick melting, an annealing at 903 K
for 7 days, and SKUT series: A quick melting, anannealing at 873 K fo 2.5 days)
The high-Pressure Synthesis (HPS) for Sm y (Fe 1x Ni x ) 4 Sb 12 sample.
Assembly for UHP-500 synthesis.
DIA-type high-pressure apparatus UHP-500 and theassembled anvil module.
XRD (RINT RAPIDⅡ(Rigaku)).
Bragg Diffraction Law.
lustration of the electron-matter interaction depicting its
different products.
SEM with energy dispersive X-ray Spectroscopy (EDX),
JSM-6510 made by JEOL.
Detector layout of JSM-6510 made by JEOL.

2

1.1.2.
2.1.1.
2.2.1.

2.2.2.
2.2.3.
2.3.1.
2.3.2.
2.3.3.

2.3.4.

2.4.1.
3.1.1.
3.1.2.
3.2.1.
3.2.2.
3.3.1.
3.3.2.
3.3.3.

3
8
10

11
16
19
21
22

23

25
29
30
32
33
35
35
36
vi

Figure

Title

Page

3.4.1.
3.4.2.
3.4.3.
3.4.4.
3.4.5.
3.5.1.

The qualitative analysis (element spector).
The EPMA color mapping.
Overall, of EPMA, JXA-8900R made by JEOL.
Mechanism of EPMA (Electron Probe Microanalyzer).
The preparing samples.
Cryostat vacuum system and sample prepration with astandard dc four-probe method.
Physical property measurement system (PPMS).
Sample prepraration for TTO.
TTO Option manager.
Chamber Control.
Baffle assembly with contact baffle.
Heat pulse and temperature and voltage response at hot
and cold thermometer Shoes in an idealized Sample.
Sample prepraration for Hall measurement.
Radiation shielding cap tool.
Resistivity Option.
File and Sample Properties dialog box.
Bridge Channels.
Data Selection.
Measurement screen.
Powder X-ray diffraction patterns of Sm y (Fe 1-x Ni x ) 4 Sb12
samples (a) and (b) for ST series and HP series,
respectively.
SEM-EDX of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples (a) and (b) for
ST series and HP series, respectively
EPMA of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples for HP series.
(a) the electrical conductivity (σ) for Sm y (Fe 1-x Ni x ) 4 Sb 12
samples of HP and ST series, and (b) the electricalresistivity (ρ) of HP and ST series.
The temperature dependence of Seebeck coefficient (S)for Sm y (Fe 1-x Ni x ) 4 Sb 12 samples of HP and ST series.
The Seebeck coefficient (S) for Sm y (Fe 1-x Ni x ) 4 Sb 12
samples as a function of (a) Ni content, (b) Fe content,and (c) Sm content at room temperature, respectively.

38
39
40
41
42
44

3.6.1.
3.6.1.1.
3.6.1.2.
3.6.1.3.
3.6.1.4.
3.6.1.5.
3.6.2.1.
3.6.2.2.
3.6.2.3.
3.6.2.4.
3.6.2.5.
3.6.2.6.
3.6.2.7.
4.1.1.

4.1.2.
4.1.3.
4.2.1.

4.2.2.
4.2.3.

45
47
48
48
49
49
51
52
52
53
53
54
54
59

62, 6364, 6568

70
70, 71vii

FigureTitle

4.2.4.

(a) The temperature dependence of the thermal
73, 74
conductivity (κ) and (b) The lattice thermal conductivity(κ L ) of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room temperature.
(a) The temperature dependence of the carrier
76
concentration (n) and (b) The mobility concentration(µ H ) of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room temperature.
ZT values as a function of the temperature of Sm y (Fe 178
x Ni x ) 4 Sb 12 samples.

4.2.5.

4.2.6.

Page

viii

LIST OF TABLES

Table

Title

Page

I.

The synthesis conditions of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples
represent the nominal composition of samples, andresults.
The composition and the lattice constant of Sm y (Fe 1x Ni x ) 4 Sb 12 samples.
The TE properties of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples atroom temperature.

58

II.
III.

66
79

ix

LIST OF ABBREVIATIONS

Abbreviation

Definition

AC
DC
EDS
EDX
EPMA
GHGs
HP
HPHT
HPS
PFs
PGEC
PPMS
RF
S
SEM
ST
TE
TECs
TEGs
TEM
TTO
WDS
XRD
ZT

Alternating current
Direct current
Energy dispersive X-ray spectrometer
Energy dispersive X-ray spectrometry
Electron probe microanalyzer
Greenhouse gases
Synthesized sample series
High-voltage high-temperature technique
High-pressure synthesis
Power factor
Phonon Glass Electron Crystal
The Physical Property Measurement System
Radio Frequency
The Seebeck coefficient
Scanning electron microscopy
Sintered sample series
Thermoelectric
Thermoelectric coolers
Thermoelectric generators
Thermoelectric modules
The Quantum Design Thermal Transport option
A wavelength dispersive X-ray analyzer
Powder X-ray diffraction
The dimensionless figure of meritxChapter 1 Introduction
1.1

Introduction
Global warming caused by global temperature rise. Whether on the air, on

the Earth's surface, or in the sea, climate change is a result of human life activities
that increase of greenhouse gases (GHGs) in the atmosphere until the greenhouseeffect due to the use of natural gas, fuel, and coal to generate electricity. It will
become dangerous to humans due to the negative impact on air pollution andglobal warming that we face in the past 100 years, with an average global
temperature rising to 0.18 0C and from the weather forecasting model 20 years
ago, the average global temperature will rise to 1.1 to 6.4 0C. (1)Currently, there is a growing interest in the use of renewable energy. To
harvest natural energy from the environment to provide sustainable, green, andinexpensive electrical energy such as heat radiation, solar energy, vibration/mechanical energy, and etc., as well as convert heat into electrical energy to
produceelectronic

devicesandindustrial

machineryisexpandingexponentially.(2) Heat energy is one of the energy sources from many places.
They can be found in many sectors such as in electronic operations, devices(integrated circuits, telephones, computers, etc.) manufactories, vehicles, in thebuilding sector, and even in the human body.
The principle of thermoelectric (TE) was discovered in 1823 by Germanscientist Thomas Seebeck, electricity flows continuously if there is a closed
circuit of the two different conductors formed and their joints kept at a hot andcold junction. The Peltier effect by Jean Charles Athanase Peltier, Peltier uses
electricity as the interface between different conductors of metal in the results of
the heat absorption circuit at one joint and the heat released at the other joints asshown in Figure 1.1.1., thermal energy transfer from p- to n-type semiconductor1

materials. The thermoelectric converter is a heat engine and, like all types ofheater engines, from thermodynamics rules. If we consider a converter that works
as an ideal generator without heat loss efficiency is defined as the ratio ofelectrical energy delivered to the load to the heat absorbed at the hot junction.
The creation of a thermoelectric unit is easy to find by considering the simplest
origin, consisting of a single thermocouple with a p-type and n-typesemiconductor.

Figure 1.1.1. Thermal energy transfer from p-type to n-typesemiconductor materials.
Thermoelectric modules (TEM) are created by the two most popular
semiconductor materials, the most commonly used are Bismuth Telluride(Bi 2 Te 3 ). They must have an electron density. different p-type and n-type,connected in parallel circuits and separated between each other by insulating
sheets. The semiconductors of p- and n-types are connected by copper strips forelectric current flow. The input is provided at the free end of the twosemiconductors, temperature differences occur at the semiconductor junctions.

2Figure 1.1.2. Thermoelectric modules (TEM) and applications.
Figure 1.1.2. shows thermoelectric modules (TEM) and applications, thepower principle can be generated by separating two conductors at hot and cold
spots by the Seebeck effect. On the other hand, the reverse of the Seebeck effectis called the Peltier effect, and the Peltier effect creates heating or cooling.(3)TE's diverse energy applications are divided into 2 major groups: 1. power
generation, based on the ability to convert temperature differences directly into
electrical energy without moving, which waste heat can be converted into
electrical energy that are useful in cars such as Thermoelectric generators (TEGs)(2), charging phone system, hand watched, radio isotope thermoelectric
generator, and etc., and 2. cooling system, the ability to convert DC electricalenergy into cooling such as thermoelectric coolers (TECs), car mini refrigerators
and air conditioning systems, small scale cooling system, medical cooler, and etc.

3

TE is widely used in many fields due to its interesting features such asenergy-saving, free maintenance, a long-life span, a high energy density, there
are no moving parts, its work is quiet and strong, and etc. The major advantage isthat it is not necessary to use toxic refrigerants that are harmful to theenvironment, but TE main weakness is due to low energy conversion efficiency(4), they become interesting in of energy harvesting for large and small
applications, depending on the size of the power output and the materials used.

1.2

Motivation
Filled skutterudite compounds are one type of TE that suitable for the useof advanced TE potentials of applications. It has been studied as one of the mostpromising TE based on state-of-the-art TE materials possess the feature of
Phonon Glass Electron Crystal (PGEC) concept (5),(6),(7) implying, these have aphonon of crystal that is “glass-like” behavior, lattice thermal conductivity like
amorphous material but an electronic structure like solid crystalline. The formula
was RT 4 X 12 , where R is guest atom such as alkali metal, alkaline earth, lanthanide,
and actinide, T is transition metals such as Fe, Ru, Os, Pt, and X is non-metals
such as P, As, Sb, Ge, respectively. The random motion (rattling)(5) of R inside
the X 12 voids to scatter the phonon in the crystal structure, which responsible fora substantial decrease in κ L to affects the electrical transport properties andenhance the Figure of merit ZT values. The devaluation efforts of κ L could cause
a decrease of κ without reducing PFs, aggregated excellent TE will result in highZT values by high S combined with high σ and low κ values.
The p-type skutterudites originated from the binary compound CoSb 3 andshown high-performance ZT value. The partial or total substitution of Co withother transition metals such as Fe and Ni provided that the electron count rule.
The successful synthesis of many R-filled R y (Fe 1-x Ni x ) 4 Sb 12 skutterudite
compounds, the p-type and the n-type skutterudite has been reported Sm fillers

4atoms get the attention of donating electrons to the crystals had improved PFs
and κ L value by rattling effect.
These substances have never been prepared by using high-pressure
synthesis (HPS) technique before, which this method helps to usually take a few
hours, estimated a decrease in synthetic temperature and the densification rate canbe improved by a pressure. The potential ZT should be achieved by carefully
expanding the areas of synthesis with the tune the Sm filling ratio, also the Fe/Ni
substitution around the p/n crossover area is attributed to the increase of S values.
The TE properties can be tuned by the Sm-filled and the substitution Fe/Ni
content, the p/n crossover of Sm y (Fe 1-x Ni x ) 4 Sb 12 at Fe ≈ 0.63, and Sm ≈ 0.31
confirmed by measurements of S values prepared by direct reaction of theelements at room-temperature, also at Fe ≈ 0.60, and Sm ≈ 0.33 confirmed bymeasurements of S values prepared by spark plasma sintering (SPS). (8)In this study, investigated the TE properties of p-type and n-type filled
skutterudites Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared by HPS technique, It was expectedsuccessfully in synthesized under high pressure using multi-anvil press made it
possible to enlarge the variation of TE material design. The optimized ZT could
be achieved by carefully expanding the research areas of synthesis with tuning
the Sm filling ratio and the Fe/Ni substitution ratio in the vicinity of the p/ncrossover point where high S values were observed.

5

1.3

References

1.

Oakes T. Asia. International Encyclopedia of Human Geography. 2009.
214–219.

2.

Jaziri N, Boughamoura A, Müller J, Mezghani B, Tounsi F, Ismail M. A
comprehensive review of Thermoelectric Generators: Technologies andcommon applications. Energy Reports. 2019.

3.

Patidar S. Applications of Thermoelectric Energy: A Review. Int J Res
Appl Sci Eng Technol. 2018;6(5):1992–6.

4.

Kang C, Wang H, Bahk JH, Kim H, Kim W. Thermoelectric materials anddevices. Vols. 2015-Janua, RSC Nanoscience and Nanotechnology.
2015;107–141.

5.

Rowe EDM, Ph D, Sc D, Group F. HANDBOOK. 2006. 72-82.

6.

Srinivasan B.

Novel chalcogenide-based glasses, ceramics andpolycrystalline materials for thermoelectric application. 2019.
7.

Nolas GS, Morelli DT, Tritt TM. Skutterudites: a phonon-glass-electron
crystal approach to advanced thermoelectric energy conversion
applications. Annu Rev Mater Sci. 1999; 29:89–116.

8.

Artini C, Castellero A, Baricco M, Buscaglia M T and Carlini R, J. Solid
State Sci. 2018;79:71-78.

6

Chapter 2 Theories and literature reviews
2.1

Thermoelectric effect
As is known that equipment is used Widely Thermoelectric (TE) Bothtemperature measurement of heating or cooling of solids and direct energy
conversion from waste heat. Based on the principle of temperature differences,the charged carriers in the material will spread to the hot side to the cold side.(1)The carrier will be moved to the cold side and discarded. Behind the opposite
charged nucleus on the hot side, causing a voltage.
The thermoelectric phenomenon allows the conversion of heat into
electricity or electricity. The phenomenon is described by three related
mechanisms: Seebeck, Peltier, and Thomson effects.(2)The Seebeck phenomenon is an important phenomenon associated withthermocouples. They are caused by bringing two types of metal conductors
connecting the ends together and heating at one connection point, causing electric
current to flow in the circuit, the value of electric current changes according to
the temperature difference at both ends of the junction as an open circuit. There
will be a voltage generated called “Seebeck voltage”.

7Figure 2.1.1. The Seebeck effect
The seebeck effect as a Figure. 2.1.1, the hot and cold junctions aremaintained at different temperatures T 1 and T 2 and T 1 > T 2 an open circuit
electromotive force (emf), V is developed, and given by
V = α (T 1 - T 2 )(1)

α = V/△T(2), where α is the differential Seebeck coefﬁcient between A and B. The
sign of α is positive if the emf causes a current to ﬂow in a clockwise direction
around the circuit and is measured in V/K.
For the Peltier phenomenon, the reverse phenomenon of the Seebeck
phenomenon is that the input of electricity into the circuit will produce one-sided
heat. Or the temperature rises to one end of junctions, the other end of junctions
is cold or the temperature drops. Causing the direction of the electric current to
be inverted. That is, the temperature on both sides is reversed, with the hot sidechanging to cold or the low temperature.

8

Thomson's results are related to the reverse heat generation rate q, whichis the result of current flows along one part of a single conductor with different
temperatures △T as shown in the equation below,q = βI△T(3), where β is Thomson coefﬁcient (V/K). The sign of α is positive if the emf
causes a current to ﬂow in a clockwise direction around the circuit and ismeasured in V/K, by considering this value as well.

2.2

Thermoelectric performance
The material potential for thermoelectric applications (conversion of heat

into electricity) is determined by the dimensionless figure of merit (ZT) is afunction of carrier concentration, electrical conductivity increases as the carrier
concentration increases as shown in the equation below,
𝑍𝑍𝑇𝑇 =

𝑆𝑆 2 𝑇𝑇𝜌𝜌𝜌𝜌=

𝑆𝑆 2 σ T𝜅𝜅𝑒𝑒 +𝜅𝜅𝑙𝑙𝜅𝜅 = 𝜅𝜅𝑒𝑒 + 𝜅𝜅𝑙𝑙

[𝐾𝐾 −1 ](4)(5), where S is the Seebeck coefficient (V/K), T is the absolute temperature(K), ρ is the electrical resistivity (Ω∙m), σ is the electrical conductivity (S/m), κ isthe total thermal conductivity (W/mK), 𝜅𝜅𝑒𝑒 is electronic thermal conductivity, and𝜅𝜅l is Lattice thermal conductivity. The electrical power factor control by 𝑆𝑆 2 σ andZT reflects the efficiency of a thermoelectric solid.

9Figure 2.2.1. The electrical conductivity, Seebeck coefﬁcient, power factor,
and thermal conductivity depend on carrier concentration.(1)The classification of materials by electrical conductivity is divided into 3
categories, high electrical conductivity is metal materials. While the low
conductivity is insulating material. The conductivity in the middle between thetwo materials is a semiconductor.
Electrical conductivity is the result of the carrier concentration and all threeparameters that occur in the Figure-of-merit as shown in Figure 1.2.1, theelectrical conductivity, Seebeck coefﬁcient, power factor, and thermal
conductivity depending on the carrier concentration. The Seebeck coefﬁcientdecreases with the electrical power factor maximizing at a carrier concentrationof around 1025/cm.(1) Generally, in thermoelectric materials is 1/3 of the total
thermal conduction increases with the carrier concentration.

10

ZT value corresponds to the semiconductor material. Therefore,
semiconductors are the most researched materials for thermoelectric applications.
ZT varies with the measurement temperature (T). ZT > 0.5 (1) are often consideredthermoelectric materials.

Figure 2.2.2. Performance of p- and n-type thermoelectric materials.
At high temperatures (> 900 K), major improvements have been made tomore than one. Figure 2.2.2. shows performance of p- and n-type thermoelectricmaterials, Si – Ge alloys, La 3-x Te 4 , Zintl phases, phonon-liquid electron-crystal(PLEC), low thermal conductivities due to the high mobility of the copper withsuperionic behavior, and oxides. It is good performance and environmental
friendliness. For telluride or related families presented the best ZT known until
now for bulk thermoelectric materials, with values of 2.2 at 915 K for p-type PbTe
doped with 4% SrTe and 2% Na, 1.6 at 775 K for the n-type doped with Ag 2Te
and La, 2.2 at 800 K for AgPb 18 SbTe 20 (LAST) n-type compound at 400-800 K(medium temperature range).(3)It can be concluded that the thermoelectric advances try to focus on the
improvement of ZT by reducing the thermal conductivity, followed by "PGEC"
concept.(1),(4) It proposed that the crystal structure with atoms or molecules with11

a gentle "rattling" bond within the atomic cage should conduct heat such as glass.
But the electrically conductive materials such as crystals, by the material
skutterudites and clathrate, have received attention due to the coherence of thisprinciple.
2.2.1 Thermoelectric parameters
Efficiency of the generator is a function of the ratio of the load resistanceto the sum of the resistance generator arms, and at the maximum output power asshown in the equation below,
𝑇𝑇 −𝑇𝑇

𝜑𝜑𝑝𝑝 = 3𝑇𝑇𝐻𝐻𝐻𝐻 𝑇𝑇𝐶𝐶 𝐶𝐶 4 1
2

+

2

+

(6)

𝑍𝑍𝐶𝐶

, where 𝑇𝑇𝐻𝐻 is hot temperature, 𝑇𝑇𝐶𝐶 is cold temperature, Z c is the Figure-of-

merit of the couple (𝑆𝑆 2 /𝜌𝜌𝜅𝜅 ′ ), where 𝜅𝜅 ′ is the thermal conductance of 2 junction

material in parallel and 𝜌𝜌 is the series resistance, while the maximum conversion

efficiency,

𝑇𝑇 −𝑇𝑇𝐶𝐶

𝜑𝜑𝑚𝑚𝑚𝑚𝑚𝑚. = 𝐻𝐻

𝑇𝑇𝐻𝐻

𝛾𝛾=

�1+𝑍𝑍𝑐𝑐 𝑇𝑇−1𝛾𝛾𝑇𝑇

�1+𝑍𝑍𝑐𝑐 𝑇𝑇+𝑇𝑇 𝐶𝐶

(7)

(8)

𝐻𝐻

𝑇𝑇 −𝑇𝑇𝐶𝐶

𝑇𝑇= 𝐻𝐻2(9)

And the maximum efﬁciency is the product of the Carnot efﬁciency, which
is clearly less than unity, and 𝛾𝛾, which embodies the parameters of the materials.

If the shapes of 2 materials (mat.1, and mat.2, respectively) match up to minimize
heat absorption,
𝑍𝑍𝑐𝑐 =

𝑆𝑆 2

1
1
𝜅𝜅
𝜅𝜅
[� mat.1 �2 +� mat.2 �2]2
𝜎𝜎mat.1
𝜎𝜎mat.2(10)

12

Then, ﬁgure-of-merit (𝑍𝑍) determines the maximum conversion efficiency
at the operating temperature, consists of three transport parameters for a material
as shown in the equation below,
𝑍𝑍=

𝑆𝑆 2 𝜎𝜎(11)𝜅𝜅, where S is the Seebeck coefficient (V/K), σ is the electrical conductivity(S/m), the electrical power factor control by 𝑆𝑆 2 σ, and κ is the total thermal

conductivity (W/mK).

Or we know as the dimensional Figure of merit (ZT), 𝑍𝑍𝑍𝑍 =𝑆𝑆 2 𝜎𝜎𝜅𝜅

𝑇𝑇. Thematerial will have a high ZT value if it has a large Seebeck coefficient, small

electrical resistance, and small thermal conductivity. In thermoelectric
semiconductor materials total thermal conductivity is an electronic thermal
conductivity (𝜅𝜅𝑒𝑒 ) and lattice thermal conductivity (𝜅𝜅𝑙𝑙 ), 𝜅𝜅 = 𝜅𝜅𝑒𝑒 + 𝜅𝜅𝑙𝑙

These three transport parameters perform depending on the carrier's

concentration, the amendment to one parameter will also affect the otherparameters, according to the law of Wiedemann-Franz law, electronic thermal
conductivity as shown in the equation below,
𝐿𝐿 𝑇𝑇𝜅𝜅𝑒𝑒 = 0

𝜌𝜌

𝐿𝐿0 =

𝜋𝜋2
3

(13)
𝜅𝜅

. ( 𝐵𝐵)2𝑒𝑒(14), where 𝐿𝐿0 is the Lorenz number, 𝜅𝜅𝐵𝐵 is Boltzmann’s constant, 𝑒𝑒 is theelectronic charge (1.6×10-19 C).

In conclusion, the electrical conductivity increases (𝜎𝜎), when the electronic
thermal conductivity (𝜅𝜅𝑒𝑒 ) increase, but no Z value increases. Therefore, thethermoelectric material, which depends on reducing the thermal conductivity (𝜅𝜅)without reducing the power factor by trying to reduce the lattice thermal
conductivity (𝜅𝜅𝑙𝑙 ).

13

2.2.2 Transport parameters
The Seebeck coefficient (𝑆𝑆) and electrical conductivity (𝜎𝜎) depend on thefermi level (𝜂𝜂∗ ), which will depend on the carrier concentration (n), carrier

effective mass (𝑚𝑚∗ ), and the temperature. Showing thermoelectric transportation

coefficient in the form of fermi energy. The thermal conductivity (𝜅𝜅) depends onthe carrier concentration, increase in the carrier concentration effect to increase
ZT value providers appears in the form of power factors (𝑆𝑆 2 σ) as shown in theequation below,𝜅𝜅𝑆𝑆 = ± 𝐵𝐵 (2.5 + 𝑠𝑠 − 𝜂𝜂∗ )𝑒𝑒𝜂𝜂 ∗ =

(15)

𝜂𝜂

(16)

𝜅𝜅𝐵𝐵 𝑇𝑇, where 𝜅𝜅𝐵𝐵 is Boltzmann’s constant, 𝑠𝑠 is the scattering parameter, ± sign isfor valence and conduction band, respectively. In heavy-doped, Seebeckcoefficient as shown in the equation below,𝜅𝜅(2+𝑠𝑠)𝐹𝐹(𝜂𝜂 ∗ )

𝑆𝑆 = ± 𝐵𝐵 ( (1+𝑠𝑠)𝐹𝐹1+𝑠𝑠(𝜂𝜂∗) − 𝜂𝜂 ∗ )𝑒𝑒∞𝐹𝐹𝑛𝑛 = ∫0

𝑠𝑠

𝑥𝑥 𝑛𝑛

1+exp (𝑥𝑥−𝜂𝜂 ∗ )

𝑑𝑑𝑑𝑑

(17)
(18)

, where 𝐹𝐹𝑛𝑛 is a Fermi integral of the order 𝑥𝑥, 𝐹𝐹𝑠𝑠 is the exponent of thecarrier's energy dependency means the free path. The distribution of the phononicor lattice vibrations of the capacitors (s=0), while the carriers are disrupted fromcharged impurities (s=2), and the mixed scattering (s=1). The transport electric
provider is represented by two mechanisms, the acoustic photons and ionized
impurities scattering dependence on the temperature of the carrier concentration(n) were 𝑇𝑇 −3/2 , 𝑇𝑇 1/2 (1), respectively.
14

The material is a single-band semiconductor that non-degenerate, theSeebeck coefficient efficiency as shown in the equation below,𝜅𝜅𝑁𝑁

𝑆𝑆 = ± 𝐵𝐵 (𝜂𝜂∗ + 𝐼𝐼𝐼𝐼 )
𝑒𝑒

𝑛𝑛

(19)

, where 𝑁𝑁 is the density of state, For the material is a single-bandsemiconductor that degenerate, the Seebeck coefficient efficiency as shown in theequation below,𝜅𝜅 2 𝑇𝑇

𝑆𝑆 = ± 𝐵𝐵 2 . 𝑚𝑚∗ .
𝑒𝑒ℎ

8𝜋𝜋4/39𝑛𝑛(20)σ, where ℎ is the Planck constant (6.63×10 -34 Js), and 𝑚𝑚∗ is the carrier

effective mass, respectively.

2.2.3 Hall Coefﬁcient, Carrier and Mobility concentration
In the year 1879, student Edwin Hall of the University of John Hoppin
found that the production of voltage (Hall voltage) across from one side of the
conductor to the other side.(5) This voltage occurs when the magnetic field isperpendicular to the surface of the conductor and the DC voltage is fed to that
conductor. The magnetic force forces the electric current from the DC voltage toflow along the edge of the conductor.
The Hall coefficient is defined as the ratio of the induced electric field tothe product of the current density and the magnetic field inserted. It is acharacteristic of the material that made the conductor Because its value depends
on the type, amount, and property of the charge carriers that make up the electric
current.

15

Figure 2.2.3. The occurrence of the hall effect.
Figure 2.2.3 shows a thin conductor sheet with width, thickness andconventional current (I) passes in the direction from the left to the right. The
charge carrier is a moving electron (velocity, V d ) in the opposite direction to thecurrent from the right to the left, while the magnetic field (B) is directed towards
and perpendicular to the plane of a thin conductor will be the magnetic force (F B )acting on the electrons causing the electrons to deflect towards the top edge ofthe thin conductor. Over time, many electrons will be pushed to the top edge. As
for the bottom border a large amount of positive charges having different charges
on both edges causing an electric field called the Hall field (E H ) in a thin
conductor having direction from the bottom edge to the top edge.
The electric field causes the electric force (F E ) acting on the electron,
which will cause the electrons to be pushed to the bottom edge. When the electricforce and the magnetic force are the same size, the electrons move in the left
direction without deflecting, electric field generated in some conductors.
In general, the energy factors of TE materials are adjusted to suit the carrier
concentration (n) by measuring Hall effect.(1)
𝑉𝑉𝐻𝐻 =

𝑅𝑅𝐻𝐻 =𝐵𝐵𝐵𝐵𝐵𝐵𝑛𝑛𝑛𝑛𝑛𝑛1

𝑛𝑛𝑛𝑛=

𝑅𝑅𝐻𝐻 𝐵𝐵𝐵𝐵
𝑡𝑡

(21)
(22)

16

, where 𝑉𝑉𝐻𝐻 is the Hall voltage (V), 𝑅𝑅𝐻𝐻 is the Hall coefﬁcient (cm3/C), 𝐵𝐵 isa magnetic ﬁeld (Oe), 𝑏𝑏 is the width of the sample and 𝑡𝑡 is the thickness, and 𝐼𝐼 isconventional current. The electrical conductivity is related to the carrier
concentration as show,
𝜎𝜎 = 𝑛𝑛. 𝑒𝑒. 𝜇𝜇 = 1/𝜌𝜌

(23)

, where 𝑒𝑒 is the elementary charge (1.6×10-19 C), 𝜇𝜇 is the carrier mobility

are important for fully characterizing and understanding a TE material. An error
in the alignment of the conductor (IR voltage) or the magnetic stripe in a straightline may cause an error. This uses a balanced three-wire hall conductor with amagnetic center bridge to eliminate any resistance. There are also other error
corrections such as the TE limit, eliminating temperature gradient, otherrestrictions. Such as van der Pauw limitations, magneto-TE characteristics, etc.

2.3

Phonon glass-electron crystal (PGEC)
We know that thermoelectric research had led to the discovery of newmaterials with improved properties. The first useful pointers are the thermal
conductivity (𝜅𝜅𝑙𝑙 ) decreases with increasing average atomic weight. It is alsosuggested that the ratio of carrier mobility (µ) to lattice conductivity increases
with atomic weight. These ideas led to the selection of Bismuth Telluride as athermoelectric material with a low value for 𝜅𝜅𝑙𝑙 , especially when it is mixed withisomorphous compounds.

The development of efficiency must have a low 𝜅𝜅𝑙𝑙 , which the filled-cagecompound has received a lot of attention. The principle called phonon-glass
electron-crystal (PGEC) that atoms are loosely bound in a large, atomic cage"rattling" which distributes heat to the acoustic phonon leads to low levels thermal
conductivity “glass-like”, these materials have lattice thermal conductivities
similar to amorphous materials but have electronic structures that can be
described as for crystalline solids developed by Slack.(4) They believe that17

electronic properties can reach modifications in this material, a great choice for
efficient thermoelectric.
PGEC can be found among skutterudites, Zintl compounds and someclathrate with Seebeck coefﬁcients in the order ± 200 mV/K or more and has alarge power factor. For example, ZT = 1.1 has been detected for Eu-filled
skutterudite at 700 K (1) and similar values for other skutterudites and someclathrate, although these materials have lower thermal conductivity than bismuth
Telluride alloys but inferior to room temperature due to the relatively small power
factor.
2.3.1 Skutterudites
Skutterudite is a type of thermoelectric material that was first discoveredin Norway in 1845. It has received popular attention with its ability todramatically reduce 𝜅𝜅𝑙𝑙 , which is facilitated by ﬁlling of cages within structures ofheavier and smaller ions in the voids will have more abnormalities that are
created, the decrease in 𝜅𝜅𝑙𝑙 of the lattice is even greater.(6)18Figure 2.3.1. Unfilled and filled-skutterudite structure.
Figure 2.3.1 shows the unfilled-skutterudite structure is a cube (with theIm3� space group (T h 5, No. 204)) and the cell unit has eight TX 3 groups, where T
is the transition metal element of VIII, IX, X group such as Fe, Ru, Os, Pt, X is

Pnictide atom of the XV group such as P, As, Sb, Ge. It has 32 atoms per unit
cell, one unit by metal atoms at an angle of eight cubes (with six (4 atoms) Sbrings inside the cubes with two voids in the remaining cubes. In the other is filled
pattern for thermoelectric, the general crystal structure of these materials can bebest described by RT 4 X 12 , which R is Alkali metal, Alkaline earth, Lanthanide(Ln), and Actinide, the existence of two voids in the structure, which are generally
by atoms of rare elements creating the most pronounced effect of reducing thethermal conductivity.(1) Other metals and pnictide sites are doped to compensate
for additional electrons from doping, a rare-earth (R), and to improve electronic
properties. Reduction of the thermal conductivity of skutterudites that are caused
rattling has a great impact on the propagation of the phonon through the lattice,attaching the 'rattlers'' more loosely bound. Produce local vibration modes oflower frequencies, heat-carrying phonons.

19

In literature as shown a great performance of filled-skutterudites, (Ce y Fe 1y ) x Co 4-x Sb 12 at T = 1,000 K had a ZT=1.4 (6),

Yb partially ﬁlled skutterudites

with ZT>1 at 600 K (4), A 19% Yb in CoSb 3 dramatically decreases 𝜅𝜅𝑙𝑙 ascompared to the unﬁlled, Yb 0.19 Co 4 Sb 12 specimen has a low 𝜅𝜅, higher than theestimated minimum 𝜅𝜅 of CoSb 3 , 𝜅𝜅 min = 0.3 W/mK. ZT~1.4 for p-type
R

DD 0.6 Fe 3 CoSb 12 at 800 K and ZT~1.9 for n-type (Sr, Ba,Yb) y Co 4 Sb 12 at 835 K(7) As shown in these examples, both p-type and n-type filled skutterudite
compounds can be synthesized depending on the filling ratio of R atom and thepartial substitution of T atom.
2.3.2 p-type and n-type filled skutterudite compounds
The thermoelectric module (TEM) consists of a thermoelectric connectionof p- and n-type in series by a lead strip (usually copper), this basic unit can still
use as a building unit for the construction of a thermoelectric conversion system.
A less complicated way for system engineers is to use TEM is building block asshown in Figure.2.3.2, the number of basic units connected by electricity in theseries. But the heat in parallel and sandwiches Between two ceramic plates. TEM
can be completed for products in various dimensions.

20

Figure 2.3.2. The basic configuration of TEM (a) basic unit, and (b) realistic
model.
In literature, p-type skutterudites originated from the binary compound
CoSb 3 and shown high-performance ZT value. The partial or total substitution of
Co with other transition metals such as Fe and Ni provided that the electron countrule.(1) The successful synthesis of many R-filled R y (Fe 1-x Ni x ) 4 Sb 12 skutterudite
compounds, the p-type skutterudites with maximum ZT value reaches 0.8 forCe 0.9 Fe 3.9 Ni 0.1 Sb 12 at 800 K sample prepared by a traditional solid-state reaction
method(8), the p-type skutterudite with maximum ZT value of 0.16 forTl 0.6 Fe 2.5 Ni 1.5 Sb 12 at 422 K sample prepared by a quenching and annealing
method(9), the n-type skutterudite had ZT reached values higher than 1 for
DD 0.76 Fe 3.4 Ni 0.6 Sb 12 at temperatures above 650 K sample prepared by a melting
reaction technique, quenching, and annealing method.(10) In addition, literature
has been reported Sm fillers atoms get the attention of donating electrons to the
crystals had improved PFs and κ L value by rattling effect. In order to separately
produce p-type and n-type skutterudites with high ZT values, we have to carefully
21

tune the carrier concentration and filling ratio of R atom. Recent studies of Fe/Nibased skutterudites Sm y (Fe 1-x Ni x ) 4 Sb 12 indicated the p/n crossover at around x= 0.37 and y = 0.31. In this system, high ZT value of 0.55 at 560 K has beenreported (11), as shown in Figure. 2.3.3. and Figure. 2.3.4

Figure 2.3.3. The p/n crossover of direct reaction of the elements at 1223
K, followed by quenching and subsequent sintering at 873 K.

22

Figure 2.3.4. p-type of Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared by Sm y (Fe 1x Ni x ) 4 Sb 12 prepared by A quick melting, an annealing. (SKUT series: A quick

melting, an annealing at 903 K for 7 days, and SKUT series: A quick melting,an annealing at 873 K fo 2.5 days)
The potential ZT should be achieved by carefully expanding the areas ofsynthesis with the tune the Sm filling ratio, also the Fe/Ni substitution around thep/n crossover area is attributed to the increase of S values. The TE properties canbe tuned by the Sm-filled and the substitution Fe/Ni content, investigated the TE
properties of p-type and n-type filled skutterudites Sm y (Fe 1-x Ni x ) 4 Sb 12 preparedby HPS technique, which this method helps to usually take a few hours, estimateda decrease in synthetic temperature and the densification rate can be improved bypressure, such as the relaxation of the n-type defects, a reduction in grain size(12) to reduce κ values, power factor (PF) resulting in improved TE properties,
the concentration of high the Sm-filled, also obtaining material properties more
rapidly, and cleanly than the other chemical techniques.

23

2.4

High-pressure synthesis technique
High-pressure synthesis is a technique that can adjust the structure andproperties of the material resulting in the synthesis of new materials. The mostcommonly used high-voltage high-temperature technique (HPHT) consists of asynthesis of a high-voltage balanced phase that can be maintained after thevoltage is released. In many cases, at medium temperatures, the voltage
conversion causes kinetic energy to be correlated in a thermodynamically stablearea in the pressure and temperature diagram (P, T).(12) HPHT is importantlaboratory-scale high-pressure tool, Bridgeman and Pistons have been developed
to synthesize excellent materials that are pressured by more than 5 GPa with avolume of about 1 cm3. They can reach a maximum pressure of 3 GPa at a volumeof less pressure zones. Bridgeman anvil can accept very high voltages dependingon the type of anvils, anvils hard alloy, the pressure ranges from 15-20 GPa, the
SiC anvils for 20–70 GPa, and diamond anvils for 100–300 GPa. A commercialpress machine that combines the concepts from anvil design. The high voltage
instrument in laboratory is the anvil diamond cell (DAC) is used extensively forsurveying high pressure synthesis and for the analysis of material properties underhigh pressure reach to 150 GPa, and can be heated easily by using infrared laserthat has over temperature 5,000 K.
The advantage of HPHT was a modify the micro and macro structure ofmaterials at the nanoscale and particle level, such as grain size, surface
morphology, structure, defects and concentration that means morphology(12),(13) and the structure of the material can be easily handled by changing
conditions P,T, the amount of High-voltage materials have demonstrated aninteresting

characteristic

among

them,

superconducting

conductors,

semiconductor, optical, electron transport, heat and dielectric, tuning pressure,and obtaining material properties quickly and thoroughly, while compared tochemical techniques.
24

The change in entropy involves relatively small volume change, whichmakes maintenance pressure easier than temperature. HPHT helps to produce thesame material as atmospheric pressure by adjusting chemicals such as adding amesh host with small atoms.(13) To stimulate the pressure of chemicals thatcreate high pressure.

Figure 2.4.1. The high-pressure synthesis (HPS) for Sm y (Fe 1-x Ni x ) 4 Sb 12 sample.
Figure. 2.4.1 shows, the high-pressure synthesis (HPS) using multiple
pressures can overcome this problem. This method allows increasing the fillingpart of the R atom in the skutterudite structure that is filled in comparison withthe conventional methods. These substances have never been prepared using
high-pressure synthesis techniques (HPS) before, which this method helps tousually take a few hours, estimated a decrease in synthetic temperature and thedensification rate can be improved by pressure, such as the relaxation of the ntype defects, a reduction in grain size to reduce κ values, power factor (PF)resulting in improved TE properties, the concentration of high the Sm-filled, also
obtaining material properties more rapidly, and cleanly than the other chemical
techniques.

25

2.5

References

1.

Rowe EDM, Ph D, Sc D, Group F. HANDBOOK. 2006.

2.

Yushanov SP, Gritter LT, Crompton JS. Multiphysics Analysis ofThermoelectric Phenomena Thermoelectric materials • Behavior describedby effect: October. 2011;0(1):1–18.

3.

Rull-Bravo M, Moure A, Fernández JF, Martín-González M. Skutterudites
as thermoelectric materials: Revisited. RSC Adv. 2015;5(52):41653–67.

4.

Nolas GS, Morelli DT, Tritt TM. Skutterudites: a phonon-glass-electron
crystal approach to advanced thermoelectric energy conversion
applications. Annu Rev Mater Sci. 1999;29:89–116.

5.

Hall EH. On a New Action of the Magnet on Electric Currents. Am J Math.
1879;2(3):287.

6.

M. Tritt T. Thermoelectric Materials : Principles , Structure , Properties ,and Applications. Encycl Mater Sci Technol. 2002;1–11.

7.

Rogl G, Grytsiv A, Royanian E, Heinrich P, Bauer E, Rogl P. New p- andn-type skutterudites with ZT > 1 and nearly identical thermal expansion
and mechanical properties. Acta Mater. 2013;61(11):4066–79.

8.

Tan G, Zheng Y, Yan Y, Tang X. Preparation and thermoelectric propertiesof p-type filled skutterudites Ce y Fe 4-x Ni x Sb 12. J Alloys Compd.
2014;584:216–21.

9.

Choi S, Kurosaki K, Ohishi Y, Muta H, Yamanaka S. Thermoelectric
properties of Tl-filled Co-free p-type skutterudites: Tl x (Fe,Ni) 4 Sb 12 . J
Appl Phys. 2014;115(2).

26

10.

Rogl G, Grytsiv A, Bauer E, Rogl P, Zehetbauer M. Thermoelectric
properties of novel skutterudites with didymium: DDy(Fe1-xCox)4Sb12
and DDy(Fe1-xNix)4Sb12. Intermetallics. 2010;18(1):57–64.

11.

Carlini R, A. U. Khan, Ricciardi R, Mori T and Zanicchi G, J. Alloys
Compd. 2016;655:321-326.

12.

Drahansky M, Paridah M., Moradbak A, Mohamed A., Owolabi F
abdulwahab taiwo, Asniza M, et al. We are IntechOpen , the world ’ sleading publisher of Open Access books Built by scientists , for scientists
TOP 1 %. Intech. 2016;13.

Taylor P. High Pressure Research : An High-pressure synthesizedmaterials : treasures and hints. 2007;(June 2012):37–41.

27

Chapter 3 Experimental methods
3.1

The high-pressure synthesis (HPS)
From the previous chapter 2 Let us know that rapid progress in technology,

which has greatly improved the pressure and temperature of the experiment inresearch. There are many levels of pressure scales from 0.1 - 500 GPa or more.
Creating a variety of high-pressure conditions for the exploration and synthesis ofmaterials requires dynamic and static compression techniques that are different frompress time. There are many physical phenomena that can be used in high voltage
techniques such as thermal expansion and phase change. High-pressure synthesis(HPS) technique, in which the volume of the sample decreases when the bearing ispressed and the high pressure generated within the sample as long as the compressionis large enough and the pressure can be maintained for a long time.(1)The skutterudite compounds of p-type and n-type Sm y (Fe 1-x Ni x ) 4 Sb 12 wereprepared high-pressure synthesis (HPS) technique by the cubic-anvil apparatus a
DIA-type of Sumitomo Heavy Industries (UHP500).(2) The samples of Sm y (Fe 1x Ni x ) 4 Sb 12 (nominal composition 0 ≤ x ≤ 0.56, 0.1 ≤y ≤ 1.2) were prepared by thefollowing two methods. The first one (Method I) was performed by direct reactionof pure elements samarium (Sm, 99.9%), iron (Fe, 99.99%), nickel (Ni, 99.99%) andantimony (Sb, 99.9999%) in quartz ampoules through the conventional meltingquenching-annealing technique; the obtained samples were subsequently ballmilled. They were mixed and sealed in a crucible fabricated of BN, and thenassembled in a cubic pyrophyllite of 16 mm3, as shown in Figure. 3.1.1., and thesintering conditions were 2 GPa and 500 oC. The second one (Method II) was thesynthesis by direct reaction of stoichiometric amounts of high-purity elements Sm,
28

Fe, Ni and Sb using HPS technique, the synthesized pressure was 2 GPa and thereaction temperature was 430 - 490 oC for 120 min.

Figure 3.1.1. Assembly for UHP-500 synthesis.

29

Figure 3.1.2. DIA-type high-pressure apparatus UHP-500 and the assembled anvil
module.
DIA-type high-pressure apparatus UHP-500 and the assembled anvil module,as shown in Figure. 3.1.2., Anvil cube modules consist of 6 anvils made by tungsten
carbide and 4 guide blocks with a 450 inclined plane. The upper and lower anvil are
fixed, while the other 4 anvils are clamped on the 4 lead blocks, it can slide on thewedge. Each anvil has a face size 1 2 ×1 2 mm2. The scrolling of the bottom frame
will press 4 anvils in a horizontal direction and press the hydrostatic can be built on

30

all 6 faces of a cubic pyrophyllite. The oil pressure system is controlled by pressing
in advance, maintaining pressure and reducing pressure patterns. The heating systemis achieved by means of heating the AC current pass from the anvil, stainless steel
rings, and Mo disks with high temperatures that can be operated between graphite.
The hole is drilled, detects the temperature by inserting a thermocouple. The
temperature inside a cubic pyrophyllite container of 16 mm3 will rise.

3.2. Powder X-ray diffraction: XRD
X-ray diffraction analysis (XRD) is a general technique for studying crystal
structures and atomic distances using creative infiltration of single X-rays andcrystal samples. It is one of the methods for analyzing microstructure used for the
crystallization. X-rays occur whenever high-speed electrons collide with metaltargets. Therefore, any X-ray tube must have an electron source, an accelerating
voltage, and a metal target. In addition, since the kinetic energy of most electrons isconverted into heat in the workpiece, water is cooled to prevent thawing. All X-ray
tubes consist of two electrodes, anode, with some exceptions, where the potential of
the soil and the cathode is still at a high level, with the typical negative potential of
about 30,000 to 50,000 volts for diffraction. X-ray tubes may be divided into twobasic types according to the method that provides electrons, there are a gas pipe that
produces electrons by making a small amount of gas, and incandescent bulbs.(3)31Figure 3.2.1. XRD (RINT RAPIDⅡ(Rigaku)).
In this work, the samples were characterized by powder X-ray diffraction
analysis (RINT RAPID II (Rigaku)) using CoKα1 radiation and silicon as a standard
at room-temperature for phase identification of crystalline material, as shown in
Figure. 3.2.1.
X-ray reflection, according to Bragg's crystal law is fired with X-rays of a
fixed wavelength, and at some point, in the incident, the strongly reflected X-rays
will occur when the wavelengths of scattered X-rays. The path must be equal to a
multiple of a wavelength. When interference occurs, the scattering beam of the Xrays causes the crystal to be at an angle equal to the incident beam as shown in theequation below,
CD + BD = nλ(1)

If CD = BD and sinθ = CD/d
CB = d hkl sinθ32

Therefore,
2 d hkl sinθ = nλ(2)Figure 3.2.2. Bragg Diffraction Law.
Bragg's diffraction in Figure. 3.2.2 is a reflection of X-rays on the surface ofthe mirror imagery caused by the plane in the crystal. Due to the nature of the crystals
repeatedly, these planes are separated by a constant distance d. Two X-ray beams ofwavelength λ arrive at the top of the imaginary plane with the incident angle θ andform as waves. In order to get a common effect after reflecting the X-ray beam, bothshould remain in phase. (Green line on the right). The situation will only occur when
the difference of the path traveled by wave fronts AC and AD (wavefronts before
and after reflection) corresponds to the integer wavelength number. This conditionis equivalent to saying that the sum of the CB and BD groups corresponds to an
integer (n) times the wavelength (λ).(3)333.3. Scanning electron microscope: SEM & EDX
Scanning electron microscopy (SEM) is an indispensable tool in research andindustry. SEM had a deeper depth and resolution than optical microscopes that aresuitable for observing complex morphology and surface height measurements. SEM
had a wide magnification range for observation from an overall perspective similar
to the naked eye to the nanostructure. SEM can install analytical capabilities tosearch for components in micron-level areas.
Energy dispersive X-ray (EDX) spectroscopy is involved in the investigationof the composition of the substance using a scanning electron microscope. EDX candetect elements with atomic numbers higher than boron and can detect theseelements at a concentration of at least 0.1%. The application of EDX includes
material evaluation and identification, contamination identification, analysis, spot
detection of areas up to 10 cm in diameter, screening, quality control, and others.
When colliding with an electron beam, in general, SEM, for example, works withthe beam and produces X-rays. Due to the principle that none of the components
have the same X-ray radiation spectrum, they can differentiate and measure theconcentration in the sample.(3)The interaction between electrons - matter, the interaction between matter electrons beam generates a variety of signals with various information about the
sample as shown in Figure 3.3.1., lustration of the electron-matter interaction
depicting its different products. For example, the reflected electrons create a contrast
image, which brings information about different atomic numbers. They can provide
information about the electronic structure and chemical composition of the material
and the electrons sent, can explain the internal structure and sample of other typesof signal crystals that are widely used in SEM are X-rays.

34

Figure. 3.3.1. lustration of the electron-matter interaction depicting its different
products.

Figure. 3.3.2. SEM with energy dispersive X-ray Spectroscopy (EDX), JSM-6510
made by JEOL.

35

Operation of SEM with energy dispersive X-ray Spectroscopy (EDX/EDS),
JSM-6510 made by JEOL as shown in Figure.3.3.2, all functions can be performed
with the software, and show in a full live image on the display computer. We can
add function keys as an option and use the adjustment function frequently by using
the key on the operation keyboard. In the large specimen chamber, the condenser
lens operation will adjust the probe current and focus during the probe current
change. It makes it quick to increase the efficiency by the probe current detector.
For sample preparation, we will attach the sample in the cylinder with carbontape, then combine it in the sampling process and insert it into the room. After that,
we will click the HT icon to open the electron source, automatically adjust thecurrent source and the camera image will appear on the operation screen. The image
sharpness is higher than the probe current. However, damage from electron
irradiation or heat increases. The current large probe reduces image resolution. But
for the reflected electron detector their High sensitivity makes the electron detector
reflect the image of the highly sensitive sample composition.

Figure. 3.3.3. Detector layout of JSM-6510 made by JEOL.
A wavelength dispersive X-ray analyzer (WDS) represent in Figure. 2.3.3,
WDS has a resolution higher than EDS, nearby spectrum peaks which are not36

modified by EDS. WDS are suitable for detecting an element of sample. EBSD
analyzes the crystal orientation of crystalline materials. The EBSD detector is
located below the EDS detector at 90 ° to the tilt axis of the specimen stage.(4)In this work, the actual chemical compositional analysis was measured byscanning electron microscopy with energy-dispersive X-ray spectrometry (SEMEDX). The nature of the SEM image will vary depending on the accelerating voltage,advice to choose the suitable voltage (Electron energy) for your specimen with thedensity and size of the structure. Normally, our laboratory uses 10 µm, 3,000 MAG.
HV 15 kV WD 15 mm conditions with 8-10 different points all phase was analyzed.

3.4. Electron Probe Microanalyzer (EPMA)
A proto-type, electron probe microanalyzer (EPMA) is a tool to analyze thecomposition of substances by electron irradiation on the surface of the substance andthe generated X-ray measurement, as shown in Figure.3.4.1. EPMA are designed
and optimized for X-ray analysis of components from very small sizes. The
accelerated electron beam that irradiates the specimen to create X-rays of secondary
electron characteristics reflected electrons and other signal ranges. EPMA detects
these signals, allowing images to be taken of samples, showing qualitative andmapping area results. Analyzing and mapping components in both micro and macro
area.

37

Figure. 3.4.1. The qualitative analysis (element spector).
Figure. 3.4.1 shows as, the qualitative analysis using independent high-speed
spectrometer and high sensitivity crystal analysis can finish in one minute, the pointand-click analysis function makes it easy to use by specifying the analytical points
on the SEM image combined with the use of the periodic table. The analysis range,
just specify the desired range in the table. It can be calculated from spectral analysis
from the spectra WDS database.

38

Figure. 3.4.2. The EPMA color mapping.
Figure. 3.4.2 shows the EPMA color mapping that has a range of micro to
macro areas. The size largest is 90 mm. The most accurate mapping is possible toreceive up to 5 data sets. The color display screen can be subdivided to be able todisplay up to 25 images at the same time and can rotate and display images in every
angle. The color level can be changed, it also has functions for point analysis, line
analysis in any direction, etc.
The instrument EPMA JXA-8900R made by JEOL is equipped with 4 X-ray
diffused wavelengths. A wavelength dispersive X-ray analyzer (WDS) and energy
dispersive X-ray Spectroscopy (EDX) combination can analyze up to 12 elements atthe same time, collecting video signals from the backscatter and the secondary
electron detector. The use of the WDS spectrometer is for a high detection sensitivity
for tracking elements, accuracy in quantitative analysis, resolving power for adjacent
X-ray spectra, and high accuracy in optical composition analysis.(5)39Figure 3.4.3. Overall, of EPMA, JXA-8900R made by JEOL.
Overall, of EPMA, JXA-8900R made by JEOL, as shows in Figure. 3.4.3,
almost all the functions can be accessed from the software. However, the function
also has access to the hardware from the console for convenience. There is an
importance part are a monitor, console/control panel features, joystick control panel,
optical microscope, and a workstation computer.

40

Figure. 3.4.4. Mechanism of EPMA (Electron Probe Microanalyzer).
The Mechanism of EPMA, when accelerated electrons hit a specimen, in
addition to the X-rays, particles and electromagnetic waves carrying various kindsof information are emitted. EPMA signals such as the characteristic-X-rays,
secondary electrons, backscattered electrons, etc. are detected by the appropriate
detectors, and that data is used to find areas of interest on the specimen and foranalysis.(5)The electrons released from the electron source are accelerated by theaccelerating voltage and are absorbed through the electron lens. An electron beamcollides with a workpiece, the X-ray is created from the workpiece by using this Xray distribution using the component distribution, the workpiece composition can beinspected. This type of spectrometer is called the X-ray wavelength dispersion
spectrometer (WDS). WDS is constructed so that the specimen surface, analyzing
crystal, and x-ray detector are positioned on a circle called the Rowland Circle, inorder to satisfy Bragg’s law, as shown in Figure. 3.4.2., mechanism of EPMA.

41

Figure. 3.4.5. The preparing samples.
In this work, the sample preparation is shown in Figure 3.4.5. The sample isattached to the cylinder with carbon tape, just like the SEM and EDX methods
mentioned in the above. Then, we will be put in the sample exchange room byobserving from the back of the sample exchange room followed in Figure 3.4.3.,
after that we will move to the next step. In our laboratory, we were analyzed 0,5,10µm, 4-8 different points of qualitative analysis from the detected X-ray wavelengths.

42

3.5. Cryostat vacuum system
The electrical properties, resistivity (ρ) values were measured by a Cryostat
vacuum system with a standard dc four-probe method. Four probe devices are oneof the standard devices and are widely used to measure semiconductor resistance.
This method is used when the sample is in the form of a thin sheet, such as a thinsemiconductor material placed on the substrate, dc four-probe arranged in a straightline in a straight line at the same distance from each other. The sample should be
adjusted to a group of squares (2.0mm×1.0mm×0.5mm) by polished with abrasive
paper No. # 3000 and #8000, respectively. The area of another 4 surfaces must be
calculated manually. To be used to fill in the program and software will calculate
the value automatically.
As we know from Chapter 2, the semiconductor has a medium conductivity
between the conductor and the insulation. The semiconductor differs from metals in
the characteristic properties of reducing electrical resistance with risingtemperatures, the semiconductor energy level can be divided into two bands, valenceband and conduction band. In front of an external electric field, it is an electron in
the valence ring that can move freely, therefore it is responsible for the conductivityof the semiconductor. In the case of semiconductors, the Fermi level is between theminimum of the thermal conductivity (𝜅𝜅) and the maximum of the capacitance.
Therefore, electrical conductivity (𝜎𝜎) cannot be achieved at 0 K and the resistanceis infinite as the temperature rises, the utilization rate of the conductivity strips
increases, resulting in reduced electrical resistance (𝜌𝜌) of the semiconductors.

43

Figure. 3.5.1. Cryostat vacuum system and sample prepration with a standard dc
four-probe method.
A constant current (I) is passed through two probes and releasing a possible(V) in two intermediate probes, as shown in Figure. 3.5.1. The cryostat vacuum
system has a controller to heat the samples in order to study the behavior of thesample when the temperature rises, we used the temperature ranges conditions ofmeasurement between 2 - 300 K.
Four probe methods, the material resistance is consistent in measurement. If
there is a minority carrier injecting into the semiconductor, the electrodes with themost current of the service providers will reassemble near the electrode so that it willaffect Little electrical conductivity. The surface of the probe head is flat without
surface leakage, four probes used for contact surfaces, measuring resistance at points

44

in a straight line. The diameter of the contact between the metal probe and thesemiconductor should be small compared to the distance between the probes. The
boundary between the current-carrying electrode and the bulk material is a halfcircle and smaller. The surface of semiconductor materials may be both operationaland non-operational. The scope of operation is what materials with a much lower
resistance than semiconductors are impregnated. Non-conductive boundaries occur
when the surface of a semiconductor is in contact with the insulation.

3.6

Physical property measurement system : PPMS
Thermal properties, including a thermal conductivity (𝜅𝜅), seebeck coefficient(S), and Hall effect were measured by The Quantum Design Thermal Transport
option (TTO) for the Physical Property Measurement System (PPMS), as shown in
Figure. 3.61

Figure. 3.6.1. Physical property measurement system (PPMS).
45

Thermal lattice conductivity (κ l ) values were calculated by subtracting κvalues with thermal electrical conductivity (κ e ) values. All measurements can beused to calculate the ZT values in the temperature range of 2 K to reach room
temperature.
3.6.1 TTO measurement
The TTO system measures the thermal conductivity or the ability of thematerial to conduct heat by checking the reduced temperature with the sample in theamount of heat known through the sample. TTO measures the effect of groundthermoelectric currents on the dropout voltage provided with reduced temperaturesin some materials. They can measure both at the same time by checking both thetemperature and the voltage drop in the sample. They use heat pulses at one end, thesystem can also measure electrical resistance by using the resistance of all four
probes.
To measure the TTO, the samples should be modified to rectangular bulk
(2.0mm×1.0mm×0.5mm), polished with abrasive paper (#3000 and #8000) andcleaned, it is can be same size with resistivity measurement, and then assembled within thermal transport sample puck that connects to the three five-pin sockets on thegreen printed circuit board, as shown in Figure. 3.6.1.1.

46

Figure. 3.6.1.1. Sample prepraration for TTO.
After that, checking the sample contact before measured, resistivity between
V+/- and I+/- with an ohmmeter. The corresponding resistivity value should be,
No.3-4 is around 200Ω, No. 5-6 is around 2 kΩ, No.7-8 is around 100Ω, No.9-10
is around 100Ω, No.11-12 and No.1-14 are show different resistivity value according
to sample property, then move to the step of measurement.
TTO Option manager, as shown in Figure. 3.6.1.2, it can be select the
Utilities-Activate Option menu command in PPMS MultiVu, select on option
thermal transport, and then select Connection Diagram button.

47

Figure. 3.6.1.2. TTO Option manager.
Before inserting the sample. It is necessary to set the inside of the chamber to
1 atm to control the pressure in the chamber, select the Vent Cont. at the Chamberstate panel as shown in Figure. 3.6.1.3. Waiting until state become flooding, theninsert the sample pack into the chamber using the sample insertion tool.

Figure. 3.6.1.3. Chamber Control.
Insert the contact baffle shielding cap tool in Figure. 3.6.1.4. into the chamber.
Select Purge / Seal at the Chamber state panel, wait until the state becomes purged,
and select High-Vac, then an active TTO option in software later.

48

Figure. 3.6.1.4. Baffle assembly with contact baffle.
After that, it will be a measurement procedure within the program. The
important part is the thermal transport waveform and the sequence writing according
to the desired measurement conditions.

Figure. 3.6.1.5. Heat pulse and temperature and voltage response at hot and cold
thermometer Shoes in an idealized Sample.(6)49Figure. 3.6.1.5., heat pulse and temperature and voltage response at hot andcold thermometer shoes in an idealized Sample, the top panel is a time tracking of
hot and cold thermometer between ideal heat pulse Note that the PPMS basetemperature fluctuates. The middle panel is corresponding temperature ∆T andvoltage ∆V, the differential in the example shows the cooling time constant τ1 andτ2, the Bottom panel is the heater power between the square wave heat pulse. The
sample should be shown a status normal waveform as same as a middle pane asshown in Figure. 3.6.1.5 before we would move to write a sequence formeasurements.
3.6.2 Hall effectAnother function for PPMS, they can measure an electric resistivity for hallmeasurement, as we know that the energy factors of TE materials are adjusted to suitthe carrier concentration (n) by measuring Hall effect from relating with 𝑉𝑉𝐻𝐻 =𝐵𝐵𝐵𝐵𝐵𝐵𝑛𝑛𝑛𝑛𝑛𝑛=𝑅𝑅𝐻𝐻 𝐵𝐵𝐵𝐵
𝑡𝑡, 𝑅𝑅𝐻𝐻 =1𝑛𝑛𝑛𝑛, where 𝑉𝑉𝐻𝐻 is the Hall voltage (V), 𝑅𝑅𝐻𝐻 is the Hall coefﬁcient(cm3/C), 𝐵𝐵 is a magnetic ﬁeld (Oe), 𝑏𝑏 is the width of the sample and 𝑡𝑡 is the
thickness, and 𝐼𝐼 is conventional current. The electrical conductivity is related to thecarrier concentration as, 𝜎𝜎 = 𝑛𝑛. 𝑒𝑒. 𝜇𝜇 = 1/𝜌𝜌 , where 𝑒𝑒 is the elementary charge(1.6×10-19 C), 𝜇𝜇 is the carrier mobility are important for fully characterizing andunderstanding a TE material.

50

Figure. 3.6.2.1. Sample prepraration for Hall measurement.
Hall measurement, the sample size should be the same as TTO measurements,
but the difference is we can assemble up to 3 samples per pack per measurement
once, as shown in Figure 3.6.2.1, sample prepraration for Hall measurement.
In PPMS Option manager for hall measurement, we can be select the UtilitiesActivate Option menu command in PPMS MultiVu, select on option resistivity forhall effect measurement, and then select Connection Diagram.
Before inserting the sample. It is necessary to set the inside of the chamber to
1 atm to control the pressure in the chamber, select the Vent Cont. at the Chamberstate panel. Waiting until the state becomes flooding, then insert the sample pack in
Figure 3.6.2.1 into the chamber using the sample insertion tool.
Insert the radiation shielding cap tool in Figure. 3.6.2.2. into the chamber.
Select Purge / Seal at the Chamber state panel, wait until the state becomes purged,
then an active resistivity option (Hall effect) in software later.

51

Figure. 3.6.2.2. Radiation shielding cap tool.
After that, it will be a measurement procedure within the program followed
in detail.
1) The resistivity option is activated, the resistivity control, the screen in
Figure 3.6.2.3, appears into the PPMS MultiVu interface. Then, create adata file. Press the Browse button in the resistivity control center Select thedrive and directory.

Figure. 3.6.2.3. Resistivity Option.
2) Enter the sample description to the File and Sample Properties dialog box
opens, as shown in Figure. 3.6.2.4. The Sample description represents theuser bridge channel that installed the sample.
52

Figure. 3.6.2.4. File and Sample Properties dialog box.

3) Select Bridge Setup in Figure. 3.6.2.5., we will set from 5000, 3000, 2000,
1000, … in current limit (μA) for check resistivity in AC and DC mode in
Drive mode, set power limit to1000 μV and Voltage limit to 95 mV to
confirm that it is not an abnormal numerical value.

Figure. 3.6.2.5. Bridge Channels.
4) Write Sequence. And then Run sequence5) Log. Open Utilities-Log PPMS Data by select Stop and then select Browse
on the General tab, and create a new folder named Log in the folder. Within53the created new folder, set the File name as the date of the measurement
date and make a file. Select Start.
6) Select View Data and Press Select All on all tabs, including the Standard
Item tab, and take Log of all items.
7) In Figure. 3.6.2.6., Data Selection will select the item you want to display
on this screen, then Figure. 3.6.2.7., it will be shown an axis.

Figure. 3.6.2.6. Data Selection.

Figure. 3.6.2.7. Measurement screen.

54

After the measurement finish, the status in the left will become Sequence Idle.
Ensure the chamber temperature is 300K. Then, open the chamber by click Vent
Cont. Button. Then open the Dewar and take off the sample. Close the Dewar andclick the Purge/Seal button to seal the chamber.

3.7

References

1.

Liu XY. High Pressure Synthesis and Preparation of Inorganic Materials.
Modern Inorganic Synthetic Chemistry: Second Edition. Elsevier B.V.; 2017.
105–141.

2.

Sekine C, Mori Y. Development of thermoelectric materials using highpressure synthesis technique. Jpn J Appl Phys. 2017;56(5):0–6.

3.

B.D. Cullity and S.R.Stock. Elements of X-RAY DIFFRACTION Second
Edition. Plant Management & Physiology. 1978. 569.

4.

JEOL. JSM-6510 series. 2012;

5.

Goodge J. Electron probe micro-analyzer (EPMA). Univ Minnesota-Duluth.
2012;2888.

6.

Design Q. Physical Property Measurement System, Thermal Transport Option
User’ s Manual. Test. 2002;(1684):77.

55

Chapter 4 Results
4.1. Sample characterization
The skutterudite compounds of p-type and n-type Sm y (Fe 1-x Ni x ) 4 Sb 12 wereprepared high-pressure synthesis (HPS) technique by the cubic-anvil apparatus a
DIA-type of Sumitomo Heavy Industries (UHP500).(1) Firstly, the compounds
were prepared by reacting stoichiometric amounts of High-purity elements
samarium (Sm, 99.9%), iron (Fe, 99.99%), nickel (Ni, 99.99%) and antimony(Sb, 99.9999%) were mixed and sealed in a crucible fabricated of BN, and thenassembled in a cubic pyrophyllite container of 16 mm3. The samples were HPS
with the approximately reaction temperature between 430 to 490 0C for 120
minutes under a pressure of about 2 GPa, are named HP series. For theconventional melting-quenching-annealing technique, the obtained samples were
subsequently ball milled. Then, samples were sintered by using a cubic-anvil
high-pressure apparatus (UHP-500, Sumitomo Heavy Industries). The sintering
conditions were 2 GPa and 500 oC for 120 minutes, are named ST series,
respectively. Bulk samples were achieved with the nominal content of Sm y (Fe 1x Ni x ) 4 Sb 12 , 0.1 ≤ Sm ≤ 1.2, and 0 ≤ Ni ≤ 0. 6, respectively.

The samples were characterized by powder X-ray diffraction analysis(RINT RAPID II (Rigaku)) using CoKα1 radiation and silicon as a standard atroom-temperature for phase identification of crystalline material. The chemicalcompositional analysis was measured by scanning electron microscopy withenergy-dispersive X-ray spectrometry (SEM-EDX) used to provide actual
elemental identification analyses 10µm with 8-10 different points all phase wasincluded, the point analysis of the qualitative analysis, and the color mapping
technique (area analysis) from electron probe microanalyzer (EPMA),
respectively. The lattice parameters (α) for the samples were calculated by theleast-squares fitting method. Table I. displays the synthesis conditions of56

Sm y (Fe 1-x Ni x ) 4 Sb 12 samples represent the nominal composition of samples, andresults.

57

58

HP2
HP3
HP4
HP5
HP6
HP7

HP1

Sm 0.5 (Fe 0.7 Ni 0.2 ) 4 Sb 12
Sm 0.3 (Fe 0.6 Ni 0.3 ) 4 Sb 12
Sm 0.1 (Fe 0.5 Ni 0.4 ) 4 Sb 12
Sm 0.04 (Fe 0.4 Ni 0.5 ) 4 Sb 12

ST2
ST3
ST4
ST5
HP7

Sm 0.2 Fe 4 Sb 12
Sm 1.0 Fe 4 Sb 12
Sm 1.2 Fe 4 Sb 12
Sm 1.2 Fe 4 Sb 12
Sm 1.2 (Fe 0.6 Ni 0.4 ) 4 Sb 12
Sm 1.0 (Fe 0.6 Ni 0.4 ) 4 Sb 12
Sm 0.8 (Fe 0.6 Ni 0.4 ) 4 Sb 12
Sm 0.6 (Fe 0.6 Ni 0.4 ) 4 Sb 12
Sm 0.4 (Fe 0.6 Ni 0.4 ) 4 Sb 12
Sm 0.2 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.2 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.8 Fe 3.8 Sb 12

ST1

Samples
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
#13
#14
#15
#16
#17
#17
#18
2

Pressure[GPa]

Conditions
Temperature
Power
[℃]
[W]
600
350
550
320
650
370
510
290
500
290
480
280
500
290
600
400
550
380
700
450
500
280
470
300
430
280
450
280
450
280
450
280
450
280
450
280
450
280
120

Time
[min]

○
○
○

△
△

○
○

△
△

×
○
×
×
×

△

×
○

△
△

Results

Table I. The synthesis conditions of Sm y (Fe 1- x Ni x ) 4 Sb 12 samples represent the nominal composition of samples, and results.

Sm (Fe Ni ) Sb(a)1-x x 412
 Sb
 SmSb (Fe,Ni)Sb

2



ST4



ST3  



530

431

422

332

600
235
026

ST5

420

330

312

Intensity (a.u.)

310

y







40

50

60

70

2θ (degree)80

Sm (Fe Ni ) Sb

431

422

332



420



HP7 

330



1-x x 412
 Sb
 SmSb (Fe,Ni)Sb

2



600

y

312

(b)
Intensity (a.u.)



310

30



235
026



ST1



530

ST2






HP6 


HP5  
HP4 




HP3



HP2 
HP1

30




















40

























50

60

2θ (degree)

70

80

Figure. 4.1.1. Powder X-ray diffraction patterns of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples(a) and (b) for ST series and HP series, respectively.

59

Powder X-ray diffraction patterns of samples can be observed in terms ofthe number of phases, Sm y (Fe 1-x Ni x ) 4 Sb 12 samples prepared under high pressure
were measured at room temperature for phase identification of polycrystalline
becomes p-type or n-type depending on composition (x and y) as shown in Figure.
4.1.1., powder X-ray diffraction patterns of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples (a) and(b) for ST series and HP series, respectively. The results revealed a similar offilled skutterudites diffraction patterns due to the same space group of them(Im 3� ). The majority of the diffraction peaks revealed the homogeneity of

Sm y (Fe 1-x Ni x ) 4 Sb 12 skutterudite phase as the main phase, and a few additional Sb,
SmSb, and (Fe , Ni)Sb 2 phase were detected in almost every compound. The
secondary phase in these compounds suggested the thermodynamically of themmore stable than the skutterudite phase that the direct combination of addition
atoms.(2) The influence of the impurity phase related to the TE transport
properties as well.
The chemical compositions by the SEM–EDX analyses of Sm y (Fe 1x Ni x ) 4 Sb 12 samples for HP and ST samples, as shown in Figure 4.1.2. SEM-EDX

of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples (a) and (b) for ST series and HP series,
respectively, the results reveled images of polished and fracture surfaces haveshown inhomogeneities. Samples have a many phase was observed by colors, thegray color is a skutterudite phase. the light gray color is a second phase also an
Sm-rich impurity phase and low Fe/Ni content identified, the dark gray color is asecond phase also a Fe/Ni-rich impurity phase and a low Sm content, the blackcolor is a second phase also a Fe-rich impurity phase, and a black dot is a porosityof samples corresponding with EPMA results in Figure 4.1.3., the color mapping
technique (area analysis), the stronger the red color on the color stripe, the more
analytical elements will be.(3) Fe/Ni content are the same area and Ni Infiltrate
the area of Fe content (white arrow and circle) and showed the distribution of Sm
content. It’s also rather inhomogeneities of the sample (4) which had many phases
60

occurred in samples. An inspection of the microphotograph of SEM-EDX andEPMA analyses indicated a component between the nominal and actual
compositions of all samples in table II., the nominal and actual compositions for
ST series and HP series, respectively.

61

62

Figure. 4.1.2. SEM-EDX of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples (a) and (b) for ST series and HP series, respectively.

63

Figure. 4.1.2. SEM-EDX of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples (a) and (b) for ST series and HP series, respectively

64

Figure. 4.1.3. EPMA of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples for HP series.

65

Figure. 4.1.3. EPMA of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples for HP series.

The lattice parameters (α) for the samples were calculated by the leastsquares fitting method, α and actual composition of Sm y (Fe 1-x Ni x ) 4 Sb 12 as shown
Table. II, Filling Sm into the voids (increasing filling fraction) lead to lattice
constant increase, and increasing Ni content according to the Vegard’s law,(5)and Ni atomic radius smaller than Fe will lead to shrink the lattice. (6),(7) The
maximum lattices constant is 9.130 Ȧ for HP1 higher than 9.091 Ȧ for HP7 thatlowest lattice constant of 0.47%, and ST samples was 9.12(9) Ȧ for ST1 higher

than 9.09(5) Ȧ for ST5 actual composition sample that lowest lattice constant of
0.27%, respectively.

Table II. The composition and the lattice constant of Sm y (Fe 1- x Ni x ) 4 Sb 12 samples.
No.

SampleNominalActualLattice constantcomposition

composition

(𝐀𝐀̇)

1.

ST1

Sm 0.8 Fe 3.8 Sb 12

Sm 0.80 Fe 4 Sb 12

9.130

2.

ST2

Sm 0.5 (Fe 0.7 Ni 0.2 ) 4 Sb 12

Sm 0.6 4(Fe 0.91 Ni 0.09 ) 4 Sb 12.4

9.111

3.

ST3

Sm 0.3 (Fe 0.6 Ni 0.3 ) 4 Sb 12

Sm 0.45 (Fe 0.73 Ni 0.27 ) 4 Sb 12.6

9.116

4.

ST4

Sm 0.1 (Fe 0.5 Ni 0.4 ) 4 Sb 12

Sm 0.14 (Fe 0.63 Ni 0.37 ) 4 Sb 12.8

9.090

5.

ST5

Sm 0.04 (Fe 0.4 Ni 0.5 ) 4 Sb 12 Sm 0.04 (Fe 0.47 Ni 0.53 ) 4 Sb 11.3

9.095

6.

HP1

Sm 1.2 Fe 4 Sb 12

Sm 0.87 Fe 4 Sb 11.3

9.134

7.

HP2

Sm 1.2 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.56 (Fe 0.54 Ni 0.46 ) 4 Sb 11.2

9.110

8.

HP3

Sm 1.0 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.36 (Fe 0.58 Ni 0.42 ) 4 Sb 11.5

9.097

9.

HP4

Sm 0.8 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.22 (Fe 0.6 Ni 0.4 ) 4 Sb 12.2

9.092

10.

HP5

Sm 0.6 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.24 (Fe 0.59 Ni 0.41 ) 4 Sb 11.2

9.101

11.

HP6

Sm 0.4 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.16 (Fe 0.63 Ni 0.37 ) 4 Sb 12.8

9.092

12.

HP7

Sm 0.2 (Fe 0.6 Ni 0.4 ) 4 Sb 12

Sm 0.09 (Fe 0.61 Ni 0.39 ) 4 Sb 12.5

9.091

66

4.2. Thermoelectric properties
The temperature dependence of electrical transport properties was shownin Figure 4.2.1. (a) the electrical conductivity (σ) for Sm y (Fe 1-x Ni x ) 4 Sb 12 samplesof HP and ST series, and (b) the electrical resistivity (ρ) of HP and ST series,
respectively. Almost samples indicated a metallic-like behavior (8) due to σvalues decreases successively with increasing temperature reaches room
temperature, except HP2, HP3, and H5 actual composition samples indicated asemiconductor behavior(9), which probably electron-hole pairs across the energy
gap from the intrinsic excitation, and the carriers being supplied by impurities
acting as dopants from heavily doped semiconductors extrinsic region (7) by σvalues decreases with increasing temperature at low temperature, then increases
continuously with increasing temperature reach room temperature. The relation
between ρ values related to σ values in the equation, σ = 1/ρ, the highest of σ of
HP samples was 0.00(2) µS/cm (the lowest ρ was 585.82 µΩ.cm) of HP6 actual
composition sample at room temperature.

67

(a) 0.02

σ (µS/cm)

0.015

HP1

HP7

HP2

ST1

HP3

ST2

HP4

ST3

HP5

ST4

HP6

ST5

0.01

0.005

0
0

(b)

50

100

150
T(K)

250

300

7000
HP1
HP2
HP3
HP4
HP5
HP6

6000
5000

ρ (µΩcm)

200

HP7
ST1
ST2
ST3
ST4
ST5

4000
3000
2000
1000
0
0

50

100

150
T(K)

200

250

300

Figure 4.2.1 (a) the electrical conductivity (σ) for Sm y (Fe 1-x Ni x ) 4 Sb 12 samples of
HP and ST series, and (b) the electrical resistivity (ρ) of HP and ST series.

68

The temperature dependence of Seebeck coefficient (S) for Sm y (Fe 1x Ni x ) 4 Sb 12 samples of HP and ST series, as displayed in Figure 4.2.2., the HP1-3

and ST1-3 sample were shown the positive S value from the majority of charge
carriers are holes. The remain HP4-7 and ST4-5 sample were shown the negative
S value indicated most charge carriers are electrons at room temperature. The
absolute value of S decreases from a maximum positive value was 56.66 μV/K of
HP1 to a maximum negative value was -68.42 μV/K of HP7 sample at room
temperature around 17.19% of absolute value. For ST samples, the absolute valueof S decreases from a maximum positive value was 56.56 μV/K of ST2 to a
maximum negative value was -47.31 μV/K of ST4 sample at room temperaturearound 19.55% of absolute value.
Figure 4.2.3. Shows the Seebeck coefficient (S) for Sm y (Fe 1-x Ni x ) 4 Sb12
samples as a function of (a) Ni content, (b) Fe content, and (c) Sm content at room
temperature, respectively, it can be observed that both 2 methods (HP and ST
samples) displayed a high value of the S around p/n crossover area with Ni content
around 0.2 to 0.4 corresponding with Fe content around 0.6 to 0.8, following to
Vegard’s law. The electrons also increased by increasing Ni-substituted for ntype skutterudites lead to the increased S value results. For a high value of the S
around p/n crossover area shown a Sm-filled around 0.6 to 0.8 for HP samples
and 0.1 to 0.3 for ST samples, respectively.

69

100
HP1
HP2
HP3
HP4
HP5
HP6

S (µV/K)

50

(a)

HP7
ST1
ST2
ST3
ST4
ST5

0

-50

-100
0

50

100

150
T(K)

200

250

300

Figure 4.2.2. The temperature dependence of Seebeck coefficient (S) for
Sm y (Fe 1-x Ni x ) 4 Sb 12 samples of HP and ST series.

(a) 8060 HP1ST2

p-typeHP synthesis
Sintered

S (µV/K)

40
20

ST1

ST3
HP3
HP2
HP4
HP5

0
-20
-40

ST4

-60

HP6 HP7

ST5n-type

-80
0

0.1

0.2

0.3
0.4
Ni content

0.5

0.6

Figure 4.2.3. The Seebeck coefficient (S) for Sm y (Fe 1-x Ni x ) 4 Sb 12 samples as afunction of (a) Ni content, (b) Fe content, and (c) Sm content at room
temperature, respectively.

70

(b) 80
HP1

ST2

60

p-typeS (µV/K)

40
20

ST1

ST3
HP3

0

HP2
HP5

HP4

ST5

-20
-40

ST4

-60

HP7 HP6

HP synthesis

n-type-80

0.5Sintered

0.6

0.7
0.8
Fe content

0.91(c) 80p-typep-type40

S (µV/K)

HP1

ST2

60

20

ST1

ST3

HP3

0
ST5

-20

n-type

HP5

HP2

HP4

n-type-40

ST4HP synthesis

-60

HP7

HP6

Sintered

-80
0

0.2

0.4
0.6
Sm content

0.8

1

Figure 4.2.3. Shows the Seebeck coefficient (S) for Sm y (Fe 1-x Ni x ) 4 Sb 12 samples
as a function of (a) Ni content, (b) Fe content, and (c) Sm content at room
temperature, respectively.

71

The temperature dependence of thermal transport properties was shown in
Figure 4.2.4. (a) the thermal conductivity (κ) of HP sample, (b) the thermal
conductivity (κ) of all samples (HP and ST samples), (c) the lattice thermal
conductivity (κ L ) of HP samples, and (d) the lattice thermal conductivity (κ L ) of
all samples (HP and ST samples), respectively. Normally, filling fraction content
addition suppresses κ values by strongly scattering thermal transport phonons,
provide scattering phonon point defect and phonon resonance with a larger filling
fraction in the literature data report. However, this experiment results, the effectsof κ values also depended on Ni/Fe content further reduce κ E values following
the Wiedmann-Franz law, the lowering electronic contribution of κ values
because of degradation in σ values, increase Ni content quite corresponding withincreasing σ values, and the dominant scattering mechanism is impurity scattering(7) in the low-temperature range as well. Figure 4.2.4. (d) displays the lowest κ Lvalue of all series (0.16 W/mK) decrease from κ value (1.31 W/mK) was 87.78 %of HP7 indicated Umklapp phonon-phonon scattering(6),(7) by increase κ L values
at low temperature and then decrease reach room temperature due to the bipolar
diffusion.(10),(11)

72

(a)

3
2.5

κ (W/m.K)

HP3
HP4

HP1
HP2

HP5
HP6

HP7

2
1.5
1
0.5
0

0

50

100

150
T(K)

200

250

300

10
(b)
8

κ (W/m.K)

HP7
ST1
ST2
ST3
ST4
ST5

HP1
HP2
HP3
HP4
HP5
HP6

6
4
2
0
0

50

100

150
T(K)

200

250

300

Figure 4.2.4. (a) (b) The temperature dependence of the thermal conductivity (κ)
of Smy(Fe1-xNix)4Sb12.

73

3

(c)

HP1
HP2

κL(W/m.K)

2.5

HP3
HP4

HP5
HP6

HP7

2

1.5
1
0.5
0
0

(d)

50

100

150
T(K)

250

300

10
HP1
HP2
HP3
HP4
HP5
HP6

8

κL(W/m.K)

200

HP7
ST1
ST2
ST3
ST4
ST5

6
4
2
0
0

50

100

150
T(K)

200

250

300

Figure 4.2.4. (c), (d) The temperature dependence of the lattice thermal
conductivity (κL) of Smy(Fe1-xNix)4Sb12.

74

The mobility concentration (µ H ) was calculated by using the equationµ H =1/ρR H , where ρ is the electrical resistivity, and R H is the Hall coefficient, thecarrier concentration (n) was calculated from R H by using the equation n =1/(eR H ), which e is the elementary charge. The symbol of R H indicated that the
major of carrier changed, the negative are electrons (n-type) and the positive areholes (p-type).(7),(3) The n should continuously decrease with increasing Ni
content due to a compensate for the electron in compounds, as shown n and µ Hvalues in Table III., the results of these experiments show the ZT values increase
with increasing temperature reaches room temperature.
Figure 4.2.5. (a) displays the temperature dependence of the carrier
concentration (n), the n values are on the order between 1019-1020 cm−3, indicateda semiconductor behavior. Figure 4.2.5. (b) displays the mobility concentration(µ H ) of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room temperature, the trend of µ H α T −3/2
behavior indicated that the acoustic phonon scattering (12) dominates at above
100 K, which corresponding with thermal transport properties as shown in Figure
5. (b), the κ L of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room temperature.

75

22

10

(a)
21

n (cm-3)

10

20

10

19

10

HP4
HP5
HP6

HP1
HP2
HP3

HP7
ST1
ST2

ST3
ST4
ST5

200

250

18

10

0

50

100

150
T(K)

300

4

10

µ (cm2 / Vs)

(b)

HP1
HP2
HP3

HP4
HP5
HP6

ST3
ST4
ST5

HP7
ST1
ST2

1000

T

-3/2

100

10

1
10

100
T(K)

Figure 4.2.5. (a) The temperature dependence of the carrier concentration (n)and (b) The mobility concentration (µ H ) of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room
temperature.

76

As the measured thermal and electrical transport properties, thedimensionless Figure of merit (ZT) value has been calculated in Figure 4.2.6. ZT
values as a function of the temperature of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples, and the
TE properties of Sm y (Fe 1-x Ni x ) 4 Sb 12 samples at room-temperature are tabulated
in Table III., respectively. The results of these experiments show the ZT values
increase with increasing temperature reaches room temperature, the highest ZT
values of 0.167(7) was achieved of HP7 sample, which is interestingly higher
than the unfilled skutterudites HP1 sample of 0.056(1) around 66.55 % at room
temperature, according to the result of the high S and the low κ interestingly werereduced by scattering of phonons. Based on these results, the maximum ZT values
adjusted by tuning Sm-filled and Fe/Ni content of these skutterudites compounds,
increasing Ni content and decreasing Sm-filled moves the maximum ZT values
possible to change this material according to the desired temperature range.

77

HP4
HP5
HP6

HP1
HP2
HP3

0.2

HP7
ST1
ST2

ST3
ST4
ST5

0.00050.15

0.0004

ZT

ZT

0.00030.00020.1

0.0001
0

0.05

0

50

100

150
T(K)

200

250

300

0
0

50

100

150
T(K)

200

250

300

Figure 4.2.6. ZT values as a function of the temperature of Sm y (Fe 1-x Ni x ) 4 Sb 12
samples.
.

78

79

Sm 0.87 Fe 4 Sb 11.3

Sm 0.56 (Fe 0.54 Ni 0.46 ) 4 Sb 11.2

Sm 0.36 (Fe 0.58 Ni 0.42 ) 4 Sb 11.5

Sm 0.22 (Fe 0.6 Ni 0.4 ) 4 Sb 12.2

Sm 0.24 (Fe 0.59 Ni 0.41 ) 4 Sb 11.2

Sm 0.16 (Fe 0.63 Ni 0.37 ) 4 Sb 12.8

Sm 0.09 (Fe 0.61 Ni 0.39 ) 4 Sb 12.5

Sm 0.80 Fe 4 Sb 12

Sm 0.6 4(Fe 0.91 Ni 0.09 ) 4 Sb 12.4

Sm 0.45 (Fe 0.73 Ni 0.27 ) 4 Sb 12.6

Sm 0.14 (Fe 0.63 Ni 0.37 ) 4 Sb 12.8

Sm 0.04 (Fe 0.47 Ni 0.53 ) 4 Sb 11.3

2. HP2

3. HP3

4. HP4

5. HP5

6. HP6

7. HP7

8. ST1

9. ST2

10.ST3

11.ST4

12.ST5

Actual composition

1. HP1

No.
(S/m)

(mΩ)

6.37E-06 1.57E+05

4.76E-06 2.10E+05

4.55E-06 2.20E+05

1.12E-05 8.93E+04

6.63E-06 1.51E+05

6.38E-06 1.57E+05

5.86E-06 1.71E+05

3.04E-05 3.29E+04

9.65E-06 1.04E+05

2.74E-05 3.65E+04

3.82E-05 2.62E+04

2.07E-05 4.83E+04

σ

ρ

κL

4.83

3.29

5.52

2.62

6.38

1.31

2.25

1.84

1.72

1.34

1.34

0.83

3.69

1.76

3.92

1.96

5.28

0.16

1.00

1.60

0.95

1.07

1.14

0.47

(W/mK) (W/mK)κ-2.08E-05-4.73E-05

1.22E-05

5.66E-05

1.77E-05-6.84E-05-6.66E-05-8.67E-06-4.06E-06

4.14E-06

1.23E-07

5.66E-05(V/K)

S

Table III. The TE properties of Sm y (Fe 1- x Ni x ) 4 Sb 12 samples at room temperature.

8.10
2.77
2.22
2.95
3.16
3.53
1.21
6.22
1.18
1.91
6.02
1.20

P
P
N
N
N
N
P
P
P
N
N

(1020cm-3)

n

P

Type

86.95

16.28

73.82

47.43

15.61

81.17

30.21

6.51

22.20

10.29

5.90

3.74

(cm2/Vs)µH

0.004(2)0.042(7)0.001(7)0.032(7)0.002(2)0.167(7)0.100(9)0.000(4)0.000(3)0.000(1)8.89E-08

0.056(1)

ZT

4.3

Summary
The skutterudite compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 were successfully

synthesized by the high-pressure synthesis (HPS) technique. The HPS can also
modify, i.e. grain size, texture, morphology, defect structure, and concentration(13),(4) by varying the pressure and temperature conditions to improve TE
properties. The TE properties concluded the results as follows, X-ray diffraction,
SEM, EDX, and EPMA results were showed skutterudite main phase, and thelattice constants were changed from the increase of Ni content as the result of
shrinking the lattice constant values. In addition, the increase of Sm-filled leads
to the increase of lattice constant value as well. The Sm-filled and Ni-substitution
effects on the TE properties of Sm y (Fe 1-x Ni x ) 4 Sb 12 series were studied by the
results of both electrical and thermal transport properties. The increase Ni content
quite corresponding with increasing σ values, also shows the low κ L value
indicated Umklapp phonon-phonon scattering by increase κ L at low temperatureand continuous decreases reach room-temperature, respectively. Furthermore,tuning Sm-filled and Fe/Ni content could be established the p-type and n-typeskutterudite. The high of S values shown around p/n crossover area with Nicontent around 0.3 corresponding with Fe content around 0.7 consist the n andµ H confirmed by Hall effect measurement. The highest ZT value of 0.167(7) isachieved for Sm 0.09 (Fe 0.61 Ni 0.39 ) 4 Sb 12.5 (HP7) actual composition of n-typeskutterudite at room temperature.

80

4.4

References

1.

Sekine C, Mori Y. Development of thermoelectric materials using highpressure synthesis technique. Jpn J Appl Phys. 2017;56(5):0–6.

2.

Mi JL, Zhao XB, Zhu TJ, Tu JP, Cao GS. Solvothermal synthesis ofnanostructured ternary skutterudite Fe 0.5 Ni 0.5 Sb 3 . J Alloys Compd.
2005;399(1–2):260–3.

3.

Rowe EDM, Ph D, Sc D, Group F. HANDBOOK. 2006. 72-82.

4.

Taylor P. High Pressure Research : An High-pressure synthesizedmaterials : treasures and hints. 2007;(June 2012):37–41.

5.

Rogl G, Grytsiv A, Royanian E, Heinrich P, Bauer E, Rogl P. New p- andn-type skutterudites with ZT > 1 and nearly identical thermal expansion
and mechanical properties. Acta Mater. 2013;61(11):4066–79.

6.

Tan G, Zheng Y, Yan Y, Tang X. Preparation and thermoelectric propertiesof p-type filled skutterudites Ce y Fe 4-x Ni x Sb 12 . J Alloys Compd. 2014;
584:216–21.

7.

Nolas GS, Morelli DT, Tritt TM. Skutterudites: a phonon-glass-electron
crystal approach to advanced thermoelectric energy conversion
applications. Annu Rev Mater Sci. 1999;29:89–116.

8.

Zhao XY, Shi X, Chen LD, Zhang WQ, Zhang WB, Pel YZ. Synthesis andthermoelectric properties of Sr-filled skutterudite Sr yCo4Sb12. J Appl
Phys. 2006;99(5).

9.

Artini C, Castellero A, Baricco M, Buscaglia M T and Carlini R, J. Solid
State Sci. 2018;79:71-78.

81

10.

Choi S, Kurosaki K, Ohishi Y, Muta H, Yamanaka S. Thermoelectric
properties of Tl-filled Co-free p-type skutterudites: Tl x (Fe,Ni) 4 Sb 12 . J
Appl Phys. 2014;115(2).

11.

Zhang J, Xu B, Yu F, Yu D, Liu Z, He J, et al. Thermoelectric propertiesof n-type CoSb 3 fabricated with high pressure sintering. 2010;503:490–3.

12.

Alboni PN, Ji X, He J, Gothard N, Tritt TM, Alboni PN, et al.
nanocomposites. 2008;113707(May 2013):3–8.

13.

Drahansky M, Paridah M., Moradbak A, Mohamed A., Owolabi F
abdulwahab taiwo, Asniza M, et al. We are IntechOpen, Intech. 2016;

82

Chapter 5 Conclusion
5.1

Conclusion
Nowadays, there is a growing interest in the use of renewable energy. To

harvest natural energy from the environment to provide sustainable, green, andinexpensive electrical energy such as RF, heat radiation, solar energy, vibration /mechanical energy, and others, as well as convert heat into electrical energy to
produce electronic devices and industrial machinery is expanding exponentially.
(1) Heat energy is one of the energy sources from many places. That can be foundin many sectors, in electronic operations, devices (integrated circuits, telephones,
computers, etc.) are working, vehicles, in the building sector, and even in thehuman body.
Thermoelectric generators (TEGs) are active devices consisting of
converting heat energy into electrical energy.(1) TEGs are made of dissimilar
thermocouples, based on the Seebeck effect, connected electrically in series andthermally in parallel. TEGs are widely used in many fields due to interesting
features such as energy-saving, free maintenance, and long-life span. They
become an interesting area in the field of energy harvesting for large and small
applications depending on the size of delivery power and materials used.
The potential of thermoelectric (TE) is evaluated by the dimensionlessfigure of merit (ZT), ZT=S2σT/κ,1,2) where S is the Seebeck coefficient, T is theabsolute temperature, σ is the electrical conductivity, and κ is the thermal
conductivity, respectively. Moreover, κ is constituted by an electronic thermal
conductivity (κ E ), directly related to σ followed by the Wiedemann-Franz law(2),(3) κ E =σL 0 T, where L 0 is the Lorentz constant (2.44×10-8 WΩ/K2), and κ L is alattice thermal conductivity.
Filled skutterudite compounds are one type of TE that suitable for the useof advanced TE potentials of applications. It has been studied as one of the most83

promising TE based on state-of-the-art TE materials possess the feature of
Phonon Glass Electron Crystal (PGEC) concept(4),(5) implying, these have aphonon of crystal that is “glass-like” behavior, lattice thermal conductivity like
amorphous material but an electronic structure like solid crystalline. The formula
was RT 4 X 12 , where R is guest atom such as alkali metal, alkaline earth, lanthanide,
and actinide, T is transition metals such as Fe, Ru, Os, Pt, and X is non-metals
such as P, As, Sb, Ge, respectively. The random motion (rattling) (4),(6) of R
inside the X 12 voids to scatter the phonon in the crystal structure, which
responsible for a substantial decrease in κ L to affects the electrical transport
properties and enhance the figure of merit ZT values. The devaluation efforts ofκ L could cause a decrease of κ without reducing PFs, aggregated excellent TE
will result in high ZT values by high S combined with high σ and low κ values.
Literature has been reported Sm fillers atoms get the attention of donating
electrons to the crystals had improved PFs and κ L value by rattling effect. The
maximum ZT value of 0.55 has been achieved for p-type of the Sm y (Fe 1x Ni x ) 4 Sb 12

skutterudites compound prepared by melting, quenching andannealing.(7) These substance has never been prepared by using high-pressure
synthesis (HPS) technique before, which this method helps to usually take a few
hours, estimated a decrease in synthetic temperature and the densification rate canbe improved by a pressure, such as the relaxation of the n-type defects, a reduction
in grain size (6), (8) to reduce κ values, power factor (PFs) resulting in improved
TE properties the concentration of high the Sm-filled, also obtaining material
properties more rapidly, and cleanly than the other chemical techniques.
The potential ZT should be achieved by carefully expanding the areas ofsynthesis with the tune the Sm filling ratio, also the Fe/Ni substitution around thep/n crossover area is attributed to the increase of S values.(9) The TE properties
can be tuned by the Sm-filled and the substitution Fe/Ni content, the p/n crossoverof Sm y (Fe 1-x Ni x ) 4 Sb 12 at Fe ≈ 0.63, and Sm ≈ 0.31 confirmed by measurementsof S values prepared by direct reaction of the elements at room-temperature(10),84also at Fe ≈ 0.60, and Sm ≈ 0.33 confirmed by measurements of S values preparedby spark plasma sintering (SPS).(11) In this study, investigated the TE propertiesof p-type and n-type filled skutterudites Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared by HPStechnique, TE properties data are evaluated, including in-depth about thepotential of TE, Sm y (Fe 1-x Ni x ) 4 Sb 12 was successfully in synthesized under highpressure, HPS using multi-anvil press made it possible to enlarge the variation of
TE material design. The highest ZT value of 0.167 was achieved for n-typeskutterudite (HP7) at room temperature.

5.1

References

1.

Jaziri N, Boughamoura A, Müller J, Mezghani B, Tounsi F, Ismail M. A
comprehensive review of Thermoelectric Generators: Technologies andcommon applications. Energy Reports. 2019;2.

Rogl G, Grytsiv A, Royanian E, Heinrich P, Bauer E, Rogl P. New p- andn-type skutterudites with ZT > 1 and nearly identical thermal expansion
and mechanical properties. Acta Mater. 2013;61(11):4066–79.

3.

Zhang J, Xu B, Yu F, Yu D, Liu Z, He J, et al. Thermoelectric propertiesof n-type CoSb 3 fabricated with high pressure sintering. 2010;503:490–3.

4.

Rowe EDM, Ph D, Sc D, Group F. HANDBOOK. 2006.

5.

Nolas GS, Morelli DT, Tritt TM. Skutterudites: a phonon-glass-electron
crystal approach to advanced thermoelectric energy conversion
applications. Annu Rev Mater Sci. 1999;29:89–116.

6.

Drahansky M, Paridah M., Moradbak A, Mohamed A., Owolabi F
abdulwahab taiwo, Asniza M, et al. We are IntechOpen, Intech. 2016.

7.

Carlini R, A. U. Khan, Ricciardi R, Mori T and Zanicchi G, J. Alloys
Compd. 2016;655:321-326.

85

8.

Taylor P. High Pressure Research : An High-pressure synthesizedmaterials : treasures and hints. 2007;(June 2012):37–41.

9.

Becker A, Schierning G, Theissmann R, Meseth M, Benson N, SchmechelR, et al. A sintered nanoparticle p-n junction observed by a Seebeck
microscan. J Appl Phys. 2012;111(5).

10.

Cristina A, Zanicchi G, Costa G A, Carnasciali M M, Fanciulli C, andCarlini R. Inorg. Chem. 2016; 55:2574-2583.

11.

Artini C, Latronico G, Carlini R, Saini S, Takeuchi T, Choi S, et al. ES
Materials & Manufacturing. 2019;12:29–37.

86Appendix A
Journals1.

Phuangyod A, Hayashi J, Kawamura Y, Artini C, Latronico G, Carlini R,
et al. Low temperature thermoelectric properties of p-type and n-type filled
skutterudite compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared under high pressure.
Jpn J Appl Phys. 2020; 061004.

2.

Sekine C, Osanai T, Ponmani H, Phuangyod A, Kawamura Y, Gotou H.
High temperature and high-pressure synthesis and magnetic properties ofarsenic-based filled skutterudite compounds. Solid State Phenom.
2019;289 SSP: 85–92.

Conference
1.

Phuangyod A, Artini C, Latronico G, Carlini R, Mele P, Kawamura Y,
Sekine C. (2019). High-pressure synthesis of filled skutterudite compounds
Sm y (Fe 1-x Ni x ) 4 Sb 12 , 60th High Pressure Conference, Japan High Pressure
Society, Sapporo, Japan, October 23, 2019.

2.

Tippayamalee P, Phuangyod A, Mele P, Kawamura Y, Sekine C. (2019).
High-pressure synthesis and physical properties of R 2 Pd 3 Ge 5 (R=Nd andYb), 60th High Pressure Conference, Japan High Pressure Society,
Sapporo, Japan, October 23, 2019.

3.

Phuangyod A, Kawamura Y, Artini C, Latronico G, Carlini R, Saini S,
Mele P, Sekine C. (2019), Thermoelectric properties of filled skutterudite
compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 using high-pressure synthesis technique,
ICT2019-

38th

International

Conferenceon

Thermoelectrics,

Gyeongju, South Korea, June 30, 2019.

87

4.

Phuangyod A, Sirimart J, Mona Y, Kawamura Y, Artini C, Latronico G,
Mele P, Sekine C. (2019). Thermoelectric properties of filled skutterudite
compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 prepared under high pressure, the Joint
Seminar on Environmental Science and Disaster Mitigation Research
2019, Muroran, Japan, March 1, 2019.

5.

Phuangyod A, Sirimart J, Mona Y, Kawamura Y, Sekine C, Artini C,
Latronico G, Mele P. (2018). The transport properties of filled skutterudite
compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 ， Muroran-IT Rare Earth Workshop
2018 ， Muroran Institute of Technology, Research Center for
Environmentally

Friendly

Materials

Engineering,

HaRP,Toya,

Hokkaido，Japan, November 8，2018.
6.

Phuangyod A, Sirimart J, Mona Y, Kawamura Y, Sekine C, Artini C,
Latronico G, Mele P. (2018). Thermoelectric properties of filled
skutterudite compounds Sm y (Fe 1-x Ni x ) 4 Sb 12 , 2018 Conference on
Electrical and Information Related Society Hokkaido Branch, Proceedingsof 2018 Conference on Electrical and Information Related Society
Hokkaido Branch, Sapporo, Japan, October 27, 2018.

Society member
1.

International Thermoelectric Society (ITS)88