bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvements in the Conductivity of n-type ZnO Through Codoping with Al and In
Authors: Kirby Steven , van Dover R. B.
Published: April 2011

ZnO has been identified as a viable candidate to replace expensive Sn doped In2O3 due to its high transparency and good conductivity. ZnO has been doped with many elements including Al and In to achieve conductivities near 104 Ω−1cm−1. One of the limiting factors in improving the conductivity beyond this is the limited solubility of these dopants in ZnO. The effect of codoping ZnO with both Al and In has been studied using a combinatorial technique. Cosputtering from three elemental targets in the presence of oxygen allowed for a range of ZnO(Al, In) compositions to be deposited on a single substrate. A deposition temperature of 250°XC was used. The films were analyzed using x-ray diffraction, electron microprobe, four-point resistivity measurements, Hall measurements, and reflection and transmission spectroscopy at optical wavelengths. Films that were codoped with both Al and In were found to have a significantly improved conductivity compared to singly doped samples, resulting mainly from an increase in mobility. This has been attributed to improved atomic structure of the codoped film. Al3+ has an ionic radius smaller than that of Zn2+ while In3+ has a larger radius; it is speculated that codoping compensates for these differences, reducing stress fields. The lattice parameter of the codoped film reflects this compensation effect.
Solution-deposited ZnO-organic diodes with high current density and high frequency rectification under ambient conditions
Authors: Pal Bhola N , Sun Jia , Jung Byung Jun , Katz Howard E
Published: April 2011

n-ZnO/p-Pentacene and n-ZnO/poly(bis(dodecyl)quaterthiophene) (p-PQT-12) vertical p-n junction diodes were prepared on ITO-coated glass. A continuous film of ZnO nanoparticles was grown on the ITO glass by dip-coating and subsequent heat treatment of a zinc acetate film. Pentacene was then thermally evaporated to form the ZnO/Pentacene diode, whereas PQT-12 was spin coated for the ZnO/PQT-12 diode. Based on the band energies of ZnO, pentacene and PQT-12, for efficient carrier injection, gold was chosen as the top electrode to complement the ITO for both diodes. The microstructures of ZnO and pentacene films are studied by AFM and show a layer of pentacene grains with about twice the extent of the underlying layer of ZnO grains, implying substantial interfacial contact between them The current density-voltage (J-V) measurement shows that the maximum current density for ZnO/Pentacene and ZnO/PQT12 are 160 A/cm2 and 350 A/cm2 respectively. The rectification was characterized by observation of full input-half output waves. Data indicate that these devices can operate up to frequencies of 20 MHz and 9 MHz for ZnO/Pentacene and ZnO/PQT12, respectively, under ambient environment conditions. This rectification frequency is higher than other reported organic and polymer Schottky diodes under these conditions. Turn on voltages of these diodes are also much lower than for the reported organic and polymer diodes.
Infrared Lattice Vibrations of Nitrogen-doped ZnO Thin Films
Authors: Hirai Makoto , Kumar Ashok
Published: April 2011

Nitrogen (N) is the most promising p-type dopant for zinc oxide (ZnO), and its bonding state must be governed by the substitution of N atoms into anion sites. We have synthesized un-doped ZnO and N-doped ZnO thin films by utilizing a pulsed laser deposition (PLD) method. The N-doped ZnO thin film possessed shorter c-axis length than the un-doped ZnO thin film. This fact seems to be owing to that Zn-N bond length is shorter than Zn-O bond length in wurtzite structure. Besides, from the result of Fourier transform infrared (FT-IR) measurement, the absorption peak of the N-doped ZnO thin film emerged at 406 cm−1, and was attributed to transverse optical (TO) phonon of E1 mode. The infrared lattice vibrations of the N-doped ZnO thin films can be induced by the complex factors consisting of not only the decreases in reduced mass and interionic distance, but also the increase in covalency.
Electrical Pumped ZnO UV Random Lasers
Authors: Yu S. , Leong Eunice Sok Ping
Published: April 2011

The realization of ZnO random cavities may be an appropriate approach to fabricate low-cost ZnO laser diodes as there is no stringent requirement in the design of the disordered media provided that they can sustain enough optical gain and feedback within the media to achieve closed-loop random lasing. However, ZnO random lasers suffer from some drawbacks such as relatively higher threshold than conventional lasers, lack of directionality and coherency light emission as well as the difficulty to realize electrically pumped ZnO random lasers. In this paper, a short review on the possibilities to realize low threshold directional electrically pumped ZnO random laser diodes.
Electrical Characterization of N+-implanted n-type ZnO Single Crystals: p-n Homojunction and Deep Level Defects
Authors: Gu Qilin , Dai Xuemin , Ling Chi-Chung , Xu Shijie , Lu Liwu , Brauer Gerhard , Anwand Wolfgang , Skorupa Wolfgang
Published: April 2011

Unintentionally doped n-type ZnO single crystals were implanted by nitrogen ions with different fluences of 1013, 1014 and 1015 cm−2 respectively. ZnO p-n homojunction was successfully fabricated due to the formation of p-type layer after 650°C post-implantation annealing in air for 30 minutes. Further thermal evolution of deep level defects was studied through thermal annealing up to 1200°C. Electrical characterization techniques including current-voltage (I-V), capacitance-voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and double-correlation DLTS (DDLTS) were used for investigating the control sample, all the as-implanted and annealed samples through Au/n-ZnO Schottky diodes as well as ZnO p-n junctions. Detailed electrical properties of fabricated devices and characteristics of implantation induced defects were analyzed based on plentiful DLTS spectra. Moreover, low-temperature photoluminescence experiments of all the as-implanted and annealed samples were performed and the correlation between results from electrical and optical characterizations was discussed.
Defects in bulk ZnO studied by steady-state and time-resolved photoluminescence
Authors: Reshchikov Michael A.
Published: April 2011

Unintentionally doped bulk ZnO samples were grown by hydrothermal method in Tokyo Denpa Co. Ltd. (Japan) and MTI Corporation. At low temperatures the PL spectrum contained a very broad band with the peak position (between 2.0 and 2.4 eV) depending on the excitation intensity. Evolution of the PL spectrum after a pulse excitation revealed that the broad band is composed of an orange (OL) and green (GL) luminescence bands having maxima at 1.96 and ∼2.35 eV, respectively. The GL band dominated at times up to 1 ms and then disappeared. The OL band decayed as approximately t−1 over a wide time interval, and its spectrum could be recorded even 24 hours after the excitation source was switched off. The slow nonexponential decay of the OL band is attributed to transitions from shallow donors to a deep acceptor (donor-acceptor pair transitions).
A Unique Method of Forming GexSi1-x Thin-Films on Insulator
Authors: Hossain Khalid , Holland O. W. , Mishima T. D. , Santos M. B. , Duggan J. L. , McDaniel F. D.
Published: April 2011

A unique process of fabricating a strained layer GexSi1−x on insulator is demonstrated. Such strained heterostructures are useful in the fabrication of high-mobility transistors. This technique incorporates well-established silicon processing technology e.g., ion implantation and thermal oxidation. A dilute GeSi layer is initially formed by implanting Ge+ into a silicon-on-insulator (SOI) substrate. Thermal oxidation segregates the Ge at the growing oxide interface to form a distinct GexSi1−x thin-film with a composition that can be tailored by controlling the oxidation parameters (e.g. temperature and oxidation ambient). In addition, the film thickness can be controlled by the implantation fluence, which is important since the film forms pseudomorphically below 2×1016 Ge/cm2. Continued oxidation consumes the underlying Si leaving the strained GeSi film encapsulated by the two oxide layers, i.e. the top thermal oxide and the buried oxide. Removal of the thermal oxide by a dilute HF etch completes the process. Strain relaxation can be achieved by either of two methods. One involves vacancy injection by ion implantation to introduce sufficient open volume within the film to compensate for the compressive strain. The other involves spontaneous relaxation of the film, which may depend, in part, upon the formation of GeO. If Ge is oxidized in the absence of Si, it evaporates as GeO(gas). Conditions under which this occurs will be discussed.
Electromigration Reliability in Nanoscale Cu Interconnects
Authors: Hu C.-K. , Gignac L. M. , Baker-O'Neal B. C. , Bonilla G. , Liniger E. G. , Flaitz P. L.
Published: April 2011

Electromigration behavior in Cu damascene wires was studied for various Cu grain struc-tures. The grain size was modulated by Cu linewidth and thickness, and by adjusting the wafer annealing process step after Cu electroplating and before Cu chemical mechanical polishing. A larger variation of Cu grain size between the samples was achieved on CMOS 65 nm node tech-nology than previous nodes which was due to the finer line width and thinner metal thickness. The Cu lifetime and mass flow in samples with bamboo, near bamboo, bamboo-polycrystalline mixture, and polycrystalline grain structures were measured. The effects of a Cu(2.5 wt.% Ti) alloy seed, Cu surface pre-clean, and selective electroless CoWP deposition techniques on Cu electromigration were also observed and a significantly improved Cu lifetime was found. The electromigration activation energies for Cu in Cu(Ti) alloy, along Cu/amorphous a-SiCxNyHz in-terface and grain boundary were found to be 1.3, 0.95 and 0.79 ± 0.05 eV, respectively. In addition the Cu line size effect on the Cu conductivity for Cu area less than 4×104 nm2 was found to be a linear function of the Cu line area.
Basic Materials Studies of Lanthanide Halide Scintillators
Authors: Doty F. P. , McGregor Douglas , Harrison Mark , Findley Kip , Polichar Raulf , Yang Pin
Published: April 2011

Cerium and lanthanum tribromides and trichlorides form isomorphous alloys with the hexagonal UCl3 type structure, and have been shown to exhibit high luminosity and proportional response, making them attractive alternatives for room temperature gamma ray spectroscopy. However the fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. In particular, low fracture stress and perfect cleavage along prismatic planes cause profuse cracking during and after crystal growth, impeding efforts to scale this system for production of low cost, large diameter spectrometers. We have reported progress on basic materials science of the lanthanide halides. Studies to date have included thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. The observed mechanical properties pose challenging problems for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Analysis of the symmetry and crystal structure of this system, including identification of densely-packed and electrically neutral planes with slip and cleavage, and comparison of relative formation and propagation energies for proposed slip systems, suggest possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. Ongoing work to develop fracture resistant lanthanide halides is presented.
Crystal Growth and Characterization of CdTe and Cd0.9Zn0.1Te for Nuclear Radiation Detectors
Authors: Mandal Krishna , Kang Sung H. , Choi Michael , Mertiri Alket , Pabst Gary W , Noblitt Caleb
Published: April 2011

CdTe and Cd0.9Zn0.1Te (CZT) crystals have been studied extensively at EIC Laboratories, Inc. for various applications including x- and γ-ray imaging and high energy radiation detectors. The crystals were grown from in-house zone refined ultra pure precursor materials using a vertical Bridgman furnace. The growth process has been monitored, controlled and optimized by a computer simulation and modeling program (MASTRAPP). The grown crystals were thoroughly characterized after sequential surface passivations and post-growth annealing treatments with and without component overpressures. The infrared (IR) transmission images of the post-treated CdTe and CZT crystals showed average Te inclusion size of ∼10 μm for CdTe crystal and ∼8 μm for CZT crystal. The etch pit density was ≤ 5×104 cm−2 for CdTe and ≤ 3×104 cm−2 for CZT. Various planar and Frisch collar detectors were fabricated and evaluated. From the current-voltage measurements, the electrical resistivity was estimated to be ∼1.5×1010 Ω·cm for CdTe and 2-5×1011 Ω·cm for CZT. The Hecht analysis of electron and hole mobility-lifetime products (μτe and μτh) showed μτe=2×10−3 cm2/V (μτh=8×10−5 cm2/V) and μτ3-6×10−3 cm2/V (μτh=4-6×10−5 cm2/V) for CdTe and CZT, respectively. Final assessments of the detector performance have been carried out using 241Am (60 keV) and 137Cs (662 keV) energy sources and the results are presented in this paper.
X-ray Topography to Characterize Surface Damage on CdZnTe Crystals
Authors: Black David , Woicik Joseph , Duff Martine C. , Hunter Douglas B. , Burger Arnold , Groza Michael
Published: April 2011

Synthetic CdZnTe or “CZT” crystals can be used for room temperature detection of α- and γ-radiation. Structural/morphological heterogeneities within CZT, such as twinning, secondary phases (often referred to as inclusions or precipitates), and polycrystallinity can affect detector performance. As part of a broader study using synchrotron radiation techniques to correlate detector performance to microstructure, x-ray topography (XRT) has been used to characterize CZT crystals. We have found that CZT crystals almost always have a variety of residual surface damage, which interferes with our ability to observe the underlying microstructure −for purposes of crystal quality evaluation. Specific structures are identifiable as resulting from fabrication processes and from handling and shipping of sample crystals. Etching was found to remove this damage; however, our studies have shown that the radiation detector performance of the etched surfaces was inferior to the as-polished surface due to higher surface currents which result in more peak tailing and less energy resolution. We have not fully investigated the effects of the various types of inducible damage on radiation detector performance.
High Temperature Functionalization and Surface Modification of Nanodiamond Powders
Authors: Mochalin Vadym N. , Osswald Sebastian , Portet Cristelle , Yushin Gleb , Hobson Christopher , Havel Mickael , Gogotsi Yury
Published: April 2011

High temperature annealing in vacuum, air, hydrogen, chlorine, and ammonia are described as a means to change surface chemistry and phase composition of nanodiamond powders of three different grades, which have different sp2/sp3carbon ratios. The changes in surface chemistry and phase composition of the powders are analyzed using Raman spectroscopy and Fourier Transform Infra Red (FTIR) spectroscopy. Advantages and limitation of high-temperature treatment techniques as well as potential applications of the gas-treated nanodiamond powders are discussed.
Triggered Single-photon Source based on Photoluminescence of Nickel-related Colour Centres in CVD-grown Nanodiamonds
Authors: Wu E , Rabeau James , Treussart François , Jacques Vincent , Zeng Heping , Prawer Steven , Grangier Philippe , Roch Jean-François
Published: April 2011

We report on the realization of a solid-state single-photon source in the near infrared at room temperature. It is based on the photoluminescence of a single NE8 colour center in a CVD grown diamond nanocrystal. Antibunching has been observed in the fluorescence light under both continuous and pulsed excitation. Our source delivers 30 kcts/s single-photon pulses at an excitation repetition rate of 20 MHz.
Mechanical Effect on Oxygen Mobility in Yttria Stabilized Zirconia
Authors: Araki Wakako , Adachi Tadaharu
Published: April 2011

The mechanical effect on the oxygen ion mobility in zirconia stabilized with 8 mol% yttria was investigated in this study. A dynamic mechanical thermal analysis showed that the dynamic modulus decreased gradually with temperature while the mechanical loss had two peaks due to different relaxation mechanisms. From the comparison of activation energies between the ionic conductivity and the mechanical relaxation, the dominant factor for oxygen mobility was determined to be the migration of oxygen vacancies in the simple complexes. An impedance analysis under mechanical tensile-loading conditions showed that the mechanical load increased ionic conductivity by 6% at maximum.
Dilute Solution of H in bcc Ti35Cr65-xVx Alloys
Authors: Mazzolai Giovanni
Published: April 2011

The solubility of H in the solid solution phase of the Ti35Cr47V18 alloy has been investigated at high and low temperature. The Sieverts law has been found to hold for 808 K≤T≤1204 K and fail for 302 K≤T≤335 K. For H contents nH ≤0.07 (nH=H/Me) the partial molar enthalpy and partial non-configurational entropy at high temperature are:

On heating the material under H2 gas pressures lower than 0.1 MPa H absorption only occurs above 700 K. Below this temperature, surface oxide films prevent H uptake. Thermal decomposition spectroscopy of the α phase carried out for nH≤0.24 exhibits a single peak whose temperature increases with decreasing nH owing to selective occupancy by H of energetically non-degenerate interstitial sites.
MgH2 by Gas Phase Condensation: Nanostructure Morphology and Hydrogen Sorption Behaviour
Authors: Bonetti Ennio , Callini Elsa , Montone Amelia , Pasquini Luca , Piscopiello Emanuela , Vittori Antisari Marco
Published: April 2011

Inert gas condensation was employed to prepare nanoparticles of Mg and MgH2 which morphology, clustering degree and structural stability have been investigated by X-ray diffraction and electron microscopy. Thermodynamic functional properties of the Mg and MgH2 nanostructured samples were investigated by high pressure differential scanning calorimetry. Some specific features of the morphology of the samples prepared by inert gas condensation are compared with powders obtained by ball milling through desorption kinetics behavior.
The Potential of Binary Lithium Magnesium Nitride - LiMgN for Hydrogen Storage Application
Authors: Lu Jun , Fang Zhigang Zak , Choi Young Joon , Sohn Hong Yong
Published: April 2011

Metal hydrides and amides are potential candidate materials for hydrogen storage. Lithium- and magnesium-based material systems are among the most promising materials owing to their high hydrogen contents. In the present work, we investigated hydrogenation/dehydrogenation reactions of a binary nitride, LiMgN. LiMgN can be formed by a reaction of MgH2 with LiNH2 in 1:1 ratio. The reaction also releases approximately ∼ 8.1 wt% H2 (theoretical value is 8.2 wt%) between 160 and 220 °C. The reaction product LiMgN can be rehydrogenated by reacting with H2 under 2000 psi of hydrogen pressure and 160 °C with small amount of TiCl3 doping. TGA results showed that about 8.0 wt% of hydrogen was stored in TiCl3-doped LiMgN during the hydrogenation process. The reversible hydrogenation and dehydrogenation mechanisms involving LiMgN and H2 are discussed.
Radiation Induced Structural Changes in Normal Spinels
Authors: Simeone David , Baldinozzi Gianguido , Gosset Dominique , Mazerolles Leo , Thome Lionel
Published: April 2011

Ion irradiation induced phase transformations in three normal spinel compounds MgAl2O4, MgCr2O4and ZnAl2O4have been investigated by X-ray diffraction, Raman spectroscopy and Transmission Electron Microscopy. This work presents a unified framework to describe the radiation effects in normal spinels. Irradiation modifies the atomic and mesoscopic structures of theses spinels in different ways. At the atomic scale, it produces the inversion of the cations in the spinel structure which can always be described within its usual Fd-3m space group. At the mesoscopic scale, it produces microdomains, responsible for the important changes in the X-ray diffraction patterns.
Defect Structure and Stability in Uranium and Zirconium Nitrides
Authors: Grimes Robin william
Published: April 2011

Atomic scale computer simulation based on a density functional approach was used to predict the behaviour of uranium, zirconiumand titanium nitrides. In addition to perfect lattice structures, defects associated with nonstoichiometry were also considered. Predictions were favourably compared with experimental data.
Insights into Radiation Tolerance of Ceramics from Large Scale Molecular Dynamics Simulations
Authors: Devanathan Ram , Weber William J.
Published: April 2011

Radiation tolerant ceramics are needed to advance the utilization of nuclear energy to meet rising global energy demand. They have potential to meet the demanding radiation environments in applications as nuclear fuel and waste forms. Their discovery and development are hampered by a lack of fundamental understanding of the physics underlying radiation tolerance of ceramics. Several theories have been advanced in the literature based on structure, radius ratio of cations and ionicity or covalency of bonds. Most of these theories focus on defect production and accumulation processes only, but neglect in-cascade and thermal annihilation of defects. We have performed large scale molecular dynamics simulations of 30 keV U and Zr recoils in zircon (ZrSiO4), zirconia (ZrO2) and yttria-stabilized zirconia (YSZ) to understand the atomic-level mechanisms that contribute to radiation tolerance, particularly fast annihilation processes. Zircon is amorphized by irradiation, while zirconia and YSZ do not undergo radiation-induced amorphization. Our results reveal that dynamic defect annihilation is very effective at controlling defect accumulation in radiation tolerant materials. Based on our results, we will discuss a strategy for improving the radiation tolerance of ceramics.
Study on Copper Precipitation under Electron Irradiation in FeCu Model Alloys by Using Vickers Hardness Measurements
Authors: Nakagawa Shou , Hori Fuminobu , Ohno Hirotaka , Ishikawa Norito , Oshima Ryuichiro , Kitagawa Michiharu , Iwase Akihiro
Published: April 2011

Three kinds of Fe-based model alloys, Fe-0.02wt%Cu, Fe-0.6wt%Cu, and Fe-1.2wt%Cu were irradiated with 2MeV electrons at 250°C. After the irradiation, the hardness was measured by using a micro Vickers hardness tester at room temperature. It was found that the hardness change by electron irradiation is proportional to the product of the copper concentration and the square root of electron fluence. The result is discussed in terms of the dispersion strengthening by Cu precipitates.
Modeling and Simulation of Thermophysical Properties of Minor Actinides-Containing Oxide Fuels
Authors: Katayama Masahito , Adachi Jun , Kurosaki Ken , Uno Masayoshi , Miwa Shuhei , Osaka Masahiko , Tanaka Kenya , Yamanaka Shinsuke
Published: April 2011

The molecular dynamics (MD) calculation was performed for minor actinide (MA: Np and Am)-containing mixed oxide (MOX) fuels, U0.7-xPu0.3MAxO2, in the temperature range from 300 to around 2500 K to evaluate the thermal expansion, heat capacity, and thermal conductivity. The MD results showed that the calculated heat capacity and thermal conductivity were similar in all the composition ranges, indicating that MA scarcely affected the thermal properties of the MOX fuel in the perfect crystal system.
Study of Fission and High-burnup Induced Restructuring of Nuclear Fuel Ceramics - Applying Computer Science to Investigate Kinetic Process
Authors: Kinoshita Motoyasu , Chen Ying , Kaneta Yasunori , Geng Hua Yun , Iwasawa Misako , Ohnuma Toshiharu , Ichinomiya Takashi , Nishiura Yasumasa , Itakura Mitsuhiro , Nakamura Jiniichi , Misoo Kiyotaka , Suzuki Soichiro , Matzke Hans J
Published: April 2011

To improve understanding of radiation damage and recovery process, especially under condition of high energy and high fluence irradiation, is currently studied at the new cross-over project (NXO). Most severe irradiation is realized by fission fragments in nuclear fuel. A guiding experiment is taken from experience in power generating Light Water Reactor (LWR) fuel. At high burnup around 7%FIMA, fuel ceramics do have restructuring of the grain sub-division where diameter of grains change down to 50 to 200 nm. The NXO investigates the process mechanism crossing over research activities of universities, national and private laboratories. Simulation studies are being performed to find principal and triggering processes, using accelerator irradiation and computational calculations. Accelerator irradiation partly succeeded to reproduce the process outside of the fission reactor using simulation material of CeO2. High resolution TEM observations, comparing microstructure changes of high burnup reactor fuel and the simulated material, shows that principal process is polygonization and indicates that Oxygen defects and planar structures, of different scales, have key role on the kinetics. Basic research works of computing science, including first principle calculations, molecular dynamics, Monte-Carlo, and meso-scale cellular automata modeling are underway.

Framework of computational study is based on understanding of the repeat of passing of fission-fragment tracks, which provide overheating and quenching cycles in time domain. It throws local atoms into higher energy quasi-stable placement and configurations. Extensive experimental observations, previously obtained and presently gained by accelerator irradiations, enable the analyses to focus into key configurations in search of the target process. Stability of planar precipitation of Xenon atomson [111] plane of the fluorite structure were demonstrated by molecular dynamics calculation. Complex kinetic processes, including stability and collective behavior, of interstitial Oxygen atoms are investigated by first principle calculations, molecular dynamics and Monte-Carlo studies.

Statistical irradiation-dynamics, for studying repeated energy-deposit cycles, may enable to draw kinetic phase diagrams. Discussions were made to have statistical counting of possible repeated traces, in relevant narrowed “investigation range” defined in time domain, configuration space and local energy.
Thermal Properties of Simulated High Burn up Nitride Fuels and Nitride ADS Targets
Authors: Uno Masayoshi , Kurosaki Ken , Yamanaka Shinsuke , Minato Kazuo
Published: April 2011

We made various nitride fuels containing simulated FP elements and evaluated the effect of these FP elements on the properties of the nitrides. For Uranium Neodymium nitride solid solution the lattice parameter increased with Nd content, thermal expansion coefficient did not change and thermal conductivity decreased with Nd content. The thermal expansion for Pd containing UN, where Pd precipitated as UPd3 in the grain boundaries of UN, was nearly the same as that of UN and the thermal conductivity for Pd containing in the UN matrix decreased with Pd content. For Mo containing UN Mo precipitated as Mo metal isotropically. Both the thermal expansion and thermal conductivity did not vary with Mo content This might result from the low Mo contents at these simulated burnups.
The Study of Solvothermal Synthesis of Nano-Engineered CoSb3 Skutterudite Thermoelectric Materials
Authors: Ji Xiaohua , He Jian , Alboni Paola N. , Tritt Terry M. , Kolis Joseph W.
Published: April 2011

Nanostructured materials have been shown to enhance phonon scattering and improve the figure of merit of thermoelectric materials. Solvothermal syntheses of nano-engineered CoSb3 skutterudite have been studied in the present work in which CoCl2 and SbCl3 were used as precursors and NaBH4 as a reductant. Elemental, structural and morphology characterization techniques including: XRD, SEM, TEM and EDAX were used to identify and characterize the products. NaBH4 was found to be a necessary factor in forming cobalt antimonide. It was detected the products' phase transited from Sb2Co to CoSb3 in conjunction with the amount increase of NaBH4. The change of synthesis time and temperature contributed little on the products' phases under the present experimental routes. Single-phased CoSb3 skutterudites was obtained from the solvothermal syntheses combined with an acid wash. The as-prepared CoSb3 powders consist of irregular nanoparticles with 15∼20 nm in size. A possible chemical mechanism was also discussed.
Oxide Thermoelectrics
Authors: Singh David Joseph
Published: April 2011

Thermoelectricity in oxides, especially NaxCoO2 and related materials, is discussed from the point of view of first principles calculations and Boltzmann transport theory. The electronic structure of this material is exceptional in that it has a combination of very narrow bands and strong hybridization between metal d states and ligand p states. As shown within the framework of conventional Boltzmann transport theory, this leads to high Seebeck coefficients even at metallic carrier densities. This suggests a strategy of searching for other narrow band oxides that can be doped metallic with mobile carriers. Some possible avenues for finding such materials are suggested.
Investigation of Cubic PbS/AgSbS2 System for Thermoelectric Applications
Authors: Todorov Iliya , Chung Duck-Young , Kanatzidis Mercouri
Published: April 2011

Investigation of a family of bulk cubic compounds with general formula AgPbmMS2+m (M = Sb, Bi) is reported. These PbS-based cubic structured quaternary systems combine a set of desirable features for efficient ZT thermoelectric materials for solar thermal power generation. AgPbmMS2+m (M = Sb, Bi) possess an average NaCl structure (Fm-3m symmetry), high melting point (991 - 1095 °C for M = Sb; 865 - 1091 °C for M = Bi), relatively wide energy gap (0.7 > Eg (eV) > 0.39 for both Sb and Bi). The systematic variation of lattice parameters, energy gap and melting point is reported. Preliminary charge transport properties are reported along with variable temperature thermal conductivity data of selected members.
High-Temperature Thermoelectric Properties of Pb1-xSnxTe:In
Authors: Jovovic Vladimir , Thiagarajan Suraj Joottu , Heremans Joseph P. , Khokhlov Dmitry , Komissarova Tanya , Nicorici Andrei
Published: April 2011

Indium in Pb1-xSnxTe alloys forms a resonant energy level in the conduction or valence bands, depending on x. In this study we investigate temperature dependence of the In level from 80 to 400K, complementing our previous work at 80 K. Measurements of electrical resistivity, thermopower, Hall and transverse Nernst-Ettinghausen effect are used to assess carrier mobility, Fermi level and scattering coefficient. Measurements are performed on a set of p and n type Pb1-xSnxTe:In with 0 < x < 30 at% and In up to 3 at%. We show that with increasing temperature the Fermi level crosses into the gap. It had been suggested theoretically that hybridization of the In level with one band at the Fermi level could have had a positive effect on the thermoelectric properties of materials, but the present results illustrate the need for temperature-dependent modeling and experimentation.
N-type Lead-Chalcogenide Thermoelectric Materials Alloyed with Tin
Authors: Koenig Jan , Jacquot Alexandre , Boettner Harald
Published: April 2011

N-type conduction was observed in epitaxial Pb1-xSnxSe and Pb1-xSnxTe thin films grown by MBE with an increasing charge carrier concentration as well as an increasing thermopower value related to an increasing tin content reaching up to 12at%. The lattice thermal conductivity decreases as expected due to alloy scattering but the carrier mobility is almost stable. All these effects increase strongly the thermoelectric properties of Pb1-xSnxSe and Pb1-xSnxTe. The n-type conduction arises from a metal excess in the stoichiometry range. The same type of conduction has also been found in bulk samples. Bulk single crystals of Pb1-xSnxSe and Pb1-xSnxTe are grown by the unseeded vapor growth technique. A rather constant mobility and a decreasing thermal conductivity with increasing tin content are measured in the n-type bulk samples. A figure of merit of ZT=0.9 was measured at 325°C for a Pb0,965Sn0,035Se sample with a carrier concentration of about 9.3E18 cm-3, i.e. already better than known n-type PbTe-based materials for this temperature range.
Silicon and Germanium Network Polyhedra viewed from Soft X-ray Spectroscopy
Authors: Tang Jun , Rachi Takeshi , Avila Marcos A , Takabatake Toshiro , Guo FagZhum , Kobayashi Keisuke , Akai Koji , Tanigaki Katsumi
Published: April 2011

The electronic states of Ba8Ga16Ge30 and Sr8Ga16Ge30 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy facility. In Ba8Ga16Ge30, three bands are resolved in the valence band region. Resonance experiments together with theoretical calculations show that the three band structures in the valence band are mainly constructed by the Ge/Ga 4s and 4p wave functions with little contributions of Ba 5s, 5p and 5d. The valence band of Sr8Ga16Ge30 shows a similar feature to that of Ba8Ga16Ge30. It is clearly shown that the atomic orbitals of Ba and Sr make little hybridization with the orbitals made by the framework polyhedra. This provides the understanding of the thermoelectricity in clathrates, and assists the design in high performance thermoelectric materials in this family.
Synthesis and Characterization of Inorganic Clathrate-II Materials
Authors: Beekman Matt , Nolas George S.
Published: April 2011

Preliminary results from an investigation into the synthesis and characterization of silicon and germanium type II clathrates are reported. A series of NaxSi136 (0 < x < 24) clathrates was synthesized and characterized by powder X-ray diffraction and Rietveld analysis. The NaxSi136 lattice parameters are observed to first decrease, then increase with increasing Na content, indicating a non-monotonic structural response to Na filling. New type II Ge clathrate compositions Cs8Na16MyGe136-y (M = Cu, In) utilizing framework substitution are reported. Electrical transport measurements on a Cu substituted specimen indicate framework substitution modifies the transport properties of these materials. The potential type II clathrate phases possess for thermoelectric applications is discussed.
Thermoelectric Properties of InxCo4-yNiySb12 Skutterudite Compounds
Authors: Da Ros Veronique , Leszczynski Juliusz , Lenoir Bertrand , Dauscher Anne , Candolfi Christophe , Masschelein Philippe , Bellouard Christine , Stiewe Christian , Mueller Eckard , Hejtmanek Jiri
Published: April 2011

The preparation of partially filled n-type InxCo4Sb12 skutterudite compounds has been recently reported. The results were particularly promising, the materials exhibiting a ZT value far higher than one at moderated temperature. In this paper, we propose to investigate another way to tune the electrical and thermal properties by substituting Co atoms by Ni atoms in InxCo4Sb12. InxCo4-yNiySb12 polycrystalline samples have been prepared by a conventional metallurgical route. Structural analyses have been carried out by X-ray diffraction. The chemical composition and micro-homogeneity have been checked by electron probe microanalysis. Measurements of the electrical resistivity, thermoelectric power and thermal conductivity have been performed between 300 and 800 K. The influence of the presence of Ni on the thermoelectric properties of InxCo4Sb12 compounds is presented and discussed.
Crystal Growth of Mg2Si by the Vertical Bridgman Method and the Doping Effect of Bi and Al on Thermoelectric Characteristics
Authors: Fukano Masataka , Iida Tsutomu , Makino Kenichiro , Akasaka Masayasu , Oguni Yohei , Takanashi Yoshifumi
Published: April 2011

Magnesium silicide (Mg2Si) has been regarded as a candidate for advanced thermoelectric materials which is used in the temperature ranging from 500 to 800 K correspond to that of vehicle exhaust emission. Besides, Mg2Si has benefits such as abundance of constituent element of Mg2Si in the earth's crust and it's non-toxicity substances compared with other thermoelectric materials that operate in the conversion temperature range such as PbTe and CoSb3. The efficiency of a thermoelectric device is characterized by the dimensionless figure of merit, ZT=S2ãT/Û, of its constituent thermoelectric material where S is the Seebeck coefficient, ã is the electrical conductivity, Û is the thermal conductivity, and T is the absolute temperature. For thermoelectric device operation, the use of a material with ZT more than unity is needed to realize a conversion efficiency of ∼10 %. The optimization of doping careers in Mg2Si is required in order to realize unity of ZT. In that way, we have grown Mg2Si crystals along with doping elements of Bi and Al using vertical Bridgman method.

Mg (99.99 %) and Si (99.99999 %) with a stoichiometric Mg : Si ratio of 67 : 33 were mixed congruently and melt into Mg2Si. Prior to the growth, Bi (99.999 %) powder at the ratio from 0.5 to 3 at % for Mg2Si and the pre-synthesized polycrystalline Mg2Si powder were mixed, and Mg2Si crystals were grown at a rate of 3 mm/h by vertical Bridgman method. Grown samples were characterized by x-ray diffraction (XRD) patterns and electron-prove microanalysis (EPMA), and the results indicated that Mg2Si crystals were reproductively grown due to use of polycrystalline Mg2Si as a source material of growth. Hall carrier concentrations were evaluated at room temperature. The electrical conductivity, the Seebeck coefficient, and the thermal conductivity were estimated in the temperature range from RT to 850 K. The grown crystals exhibited n-type conductivity in undoped and all Bi doped conditions. All the Bi doped crystals showed high electrical conductivity and high carrier concentration compared with that of the undoped crystal. On the other hand, the thermal conductivity was lowered in the proportion of the amount of Bi. Consequently, the thermal conductivity for the crystal that was Bi doped at 3 at % was 0.021 W/cmK at 842K, and its ZT reached 0.99 at 842 K, which is near the unity of ZT that is regarded as a standard of practical use for thermoelectric materials. The solid solubility limit of Bi to Mg2Si was assumed to be around 3 at % from our findings, and thus Al was codoped besides Bi in order further to improve the thermoelectric properties. We will discuss the results, additionally.
Doping Characteristics of Silver in Mg2Si1-xGex Prepared by Plasma Activated Sintering
Authors: Nemoto Takashi , Sato Junichi , Iida Tsutomu , Akasaka Masayasu , Matsumoto Atsunobu , Nakajima Tadao , Nishio Keishi , Takanashi Yoshifumi
Published: April 2011

Silver (Ag) doped Mg2Si1-xGex (x=0.1 to 0.4) samples were fabricated using a plasma activated sintering (PAS) method. The doping concentration of Ag was varied from 1 to 5 at.%. Undoped Mg2Si1-xGex exhibits n-type conductivity due to residual impurities in the Mg source material used and unintentionally process-induced impurities. The observed unstable behavior of the Seebeck coefficient of Ag-doped p-type Mg2Si1-xGex (x ≤ 0.3) in the region of 550 to 650 K, exhibiting a considerable drop in the value and occasional conduction type conversion, was correlated with the specific contaminants. For x∼0.4, the observed Seebeck coefficient varied from 0.2 mV/K at 823 K to 0.4 mV/K at room temperature, with no remarkable drop in the value with increasing temperature. An estimated ZT value of 5 at.% Ag doped Mg2Si0.6Ge0.4 was 0.18 at 844 K. It was found that both specific residual impurities and process-induced impurities affected the characteristics of the Seebeck coefficient of Mg2Si1-xGex.
Improvement of Thermoelectric Properties of p- and n-types Oxide Thick Films Fabricated by Electrophoretic Deposition
Authors: Sakurai Masayuki , Horii Shigeru , Funahashi Ryoji , Uchikoshi Tetsuo , Suzuki Tohru , Sakka Yoshio , Ogino Hiraku , Shimoyama Jun-ichi , Kishio Kohji
Published: April 2011

We report thermoelectric (TE) properties of mono-layer thick films of p-type [Ca2CoO3-δ]0.62CoO2 (Ca349) and n-type compounds of Ca0.9La0.1MnO3 (Mn113) and LaNi0.98Mo0.02O3 (Ni113) for the improvement of TE performance in multi-layered TE modules. In the case of magnetically aligned Ca349 film, the improvement of TE properties due to the reduction of resistivity (ρ) was achieved by optimization of hot-pressing temperature and ρ was sensitive to relative density of the Ca349 layer. For the decrease in ρ of the n-type layers, two different approaches, the choice of Ni113 as a n-type compound and usage of fine powders of Mn113, were attempted. Both approaches were effective for reducing ρ even in the sintering at ∼900°C.
Power and Efficiency Calculation and Evaluation of Material Properties in Thermoelectric Power Generators
Authors: Zorbas Konstantinos , Hatzikraniotis Euripides , Paraskevopoulos Konstantinos M
Published: April 2011

Thermoelectric elements convert a part of thermal power into electrical, developing the Seebeck effect. A number of thermoelectric elements can be connected electrically in parallel and/or in series shaping a thermoelectric generator (TEG) device. The generator efficiency, η, is determined by comparing the amount of electricity produced (PTEG) to the total amount of heat induced (QH). The possible use of such a device for the recovery of wasted heat can considerably help the world effort for energy savings and the reduction of greenhouse gases.

A measuring system and a modeling approach which takes into account the thermal contact resistances have been developed, allowing the characterization of TEG devices under various loads and temperature gradients and thus, the evaluation of material properties. The model was applied on investigating the expected gained power and efficiency, at different places of the exhaust pipe of an intermediate size car with the use of conventional thermoelectric elements. Furthermore, the reliability of a TEG module was examined and the repercussion on fuel consumption is discussed.
Enhanced Cooling in Doped Semiconductors Due to Nonlinear Peltier Effect
Authors: Zebarjadi Mona , Esfarjani Keivan , Shakouri Ali
Published: April 2011

Thermoelectric coefficients become a function of the applied field and temperature gradient if the latter become large enough. So in analyzing device performance in this regime accurately, it is important to include the non-linear terms. Non-linearity is a consequence of electron heating. For low doping concentrations, nonlinearity can happen at low currents. We will show that at room temperature in InGaAs it starts at practical currents on the order of 105 A/cm2. At low temperatures the Peltier coefficient goes to zero. However, its nonlinear term does not change as much. Since the nonlinear heat current goes with the third power of current, there is a chance that in some cases it can overcome the joule heating. We will show that at T=77K the cooling power can be enhanced by a factor of seven compared to room temperature. Nonlinearity of the Seebeck coefficient becomes an important factor when high temperature gradients are applied on nanoscale samples, and can lead to enhanced power generation
Synthesis and thermoelectric properties of antifluorite materials
Authors: Lin Xiunu Sophie , Wang Dongli , Beekman Matthew , Nolas George
Published: April 2011

The compounds Mg2X (where X=Si, Ge, Sn) crystallize in the antifluorite structure. They possess properties that are similar to that of the group IV elemental semiconductors thus they have long been recognized as good candidates for thermoelectric applications. In addition, their properties can be readily tuned by doping or alloying. However, optimal performance of these materials requires continued investigation. We present low-temperature transport properties measurements of Sb doped Mg2X. Structure-property relationships are reported while their thermoelectric properties are investigated systematically in order to elucidate their potential as thermoelectric materials.
Change in Activation Volume for Plastic Deformation of Zr-based Bulk Metallic Glass following Annealing
Authors: Puthoff Jonathan B. , Stone Donald S. , Cao Hongbo , Voyles Paul M.
Published: April 2011

We performed nanoindentation creep experiments on the bulk metallic glass Zr54Cu38Al8 in an effort to measure the scale of the individual deformation events responsible for plastic deformation. From a nanoindentation creep experiment, we can determine V*, the activation volume, which we interpret as the volume of a shear transformation zone (STZ) multiplied by the shear strain undergone by the STZ during thermal activation. For the as-cast alloy hardness, H, is 5.33 ± 0.06 GPa, and V* is 87 ± 5 Å3. The alloy was then annealed near Tg for 24 hr and retested. No crystallization occurred during annealing as verified by XRD and TEM. Following annealing H increased to 7.36 ± 0.08 GPa and V* increased to 160 ± 10 Å3. We interpret the change in V* as arising from an increase in the number of atoms involved in the STZ.
Geometry-sensitive plasticity of a monolithic bulk metallic glass
Authors: Wu WenFei , Li Yi
Published: April 2011

We report a strong geometry-dependence of compressive plasticity in a Zr-based bulk metallic glass (BMG). With a standard orthogonal geometry, the Zr-based BMG typically fractured at a plastic strain less than 2%. However, by modifying the sample geometry while maintaining the sample aspect ratio, a large apparent compressive plastic strain over 10% was achieved consistently. These results present a new method on arresting the catastrophic failure of the glassy alloys and offer ways for BMGs in engineering applications.
Phase Stability of Crystalline and Amorphous Phases and Formation of Nanostructure in Zr-Pd and Zr-Pt Alloys Under Electron Irradiation
Authors: Umakoshi Yukichi , Nagase Takeshi , Hosokawa Takashi
Published: April 2011

Electron irradiation induced phase transition behavior of Zr-Pd and Zr-Pt alloys was investigated focusing on phase selection in crystallization by thermal annealing and electron irradiation. Nano quasi-crystalline (QC) phase was formed by thermal crystallization in Zr66.7Pd33.3 and Zr80Pt20 alloys, while nano two-type f.c.c. super-saturated solid solutions were formed by irradiation induced crystallization at 298K. In Zr66.7Pt33.3 alloy, polycrystalline Zr5Pt3 and Zr9Pt11 phases transformed to two-type f.c.c. nano-crystalline phase through an amorphous state by crystal-to-amorphous-to-crystal (C-A-C) transition during electron irradiation. Nano-composite phase composed of f.c.c. super-saturated solid solution and residual amorphous phase was stable rather than an amorphous single phase, thermal equilibrium crystalline phase and quasi-crystalline phase under 2.0MV electron irradiation at 298K, resulting in the formation of nano-composite structure by irradiation induced amorphization and crystallization.