Query: crystal structure of new Heusler Compounds

Candidate papers:

abstract: Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the the crystal structure. In general, Heusler compounds crystallize in the Cu2MnAl type structure but in many cases certain types of disorder are observed. In this paper a detailed description of the different types of disordered structures is given. Additionally, the synthesis of new Heusler compounds is reported. The prepared compounds contain ternary Cr Rh Ru Ni Pd and Pt based Heusler systems as well as quaternary Co2 based compounds and compounds of the general formula XXYZ. The crystal structure was determined by XRD measurements and the structural ordering of the compounds is discussed.
author_names: Tanja Graf

Frederick Casper

Juergen Winterlik

Benjamin Balke

Gerhard H Fecher

Claudia Felser
title: Crystal Structure of New Heusler Compounds
year: 2009

abstract: The present work reports on the new soft ferromagnetic Heusler phases Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been predicted to exist in a tetragonal regular Heusler structure. Together with the known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and characterized by powder XRD, 57 Fe M\"ossbauer spectroscopy, SQUID and EDX measurements. In particular M\"ossbauer spectroscopy was used to monitor the degree of local atomic order/disorder and to estimate magnetic moments at the Fe sites from the hyperfine fields. It is shown that in contrast to the previous predictions all the materials except Fe2NiGa basically adopt the inverse cubic Heusler (X structure with differing degrees of disorder. The disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse Heusler phase. The experimental data are compared with results from ab inito electronic structure calculations on LDA level incorporating the effects of atomic disorder by using the coherent potential approximation (CPA) A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases. Model calculations on various atomic configurations demonstrate that antisite disorder tends to enhance the stability of the X structure. Given the fundamental scientific and technological importance of tetragonal Heusler phases the present results call for further investigations to unravel the factors stabilizing tetragonal Heusler materials.
author_names: Teuta Gasi

Vadim Ksenofontov

Janos Kiss

Stanislav Chadov

Ajaya K Nayak

Michael Nicklas

Juergen Winterlik

Michael Schwall

Peter Klaer

Peter Adler

Claudia Felser
title: Iron based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
year: 2013

abstract: Abstract The crystal structure, electronic and magnetic properties of predicted new full Heusler compounds Zr 2 MnZ (Z=Al, Ga, In) were studied within the density functional theory (DFT) framework. These materials exhibit unique properties that connect the spin gapless semiconducting character with the completely compensated ferrimagnetism. Magnetically ordered Zr 2 MnZ (Z=Al, Ga, In) compounds crystallize in inverse Heusler structure are stable against decomposition and have zero magnetic moment per formula unit, in agreement with Slater Pauling rule. The Zr 2 MnAl compound presents semiconducting properties with an energy band gap of 0.41 eV in the majority spin channel and a zero band gap in the minority spin channel. By substituting completely the Al in Zr 2 MnAl via Ga and In elements, semiconducting pseudo band gaps are formed in the majority spin channels due to different neighborhoods around the manganese atoms, which decreases the energy of Mn triple degenerated anti bonding states.
author_names: A Birsan
title: First principle investigations of the structural, electronic and magnetic properties of predicted new zirconium based full Heusler compounds, Zr2MnZ (Z=Al, Ga and In)
year: 2016

abstract: In this work, half metallic (HM) properties of new Half Heusler (HH) ferromagnetic compounds CrTiX (X Si, Ge, Sn, Pb) are studied by means of first principle band structure calculation within the framework of density functional theory (DFT) From the spin polarized calculations using full potential linearized augmented plane wave (FP LAPW)method, we found that all of these compounds are stable in ferromagnetic MgAgAs type crystal structure. The latticeparameters of CrTiX compounds increase with increasing atomic radius of X atom and ranges from 5.76 to 6.38 A. The calculated electronic structure of these compounds in MgAgAs type structure shows that they are HM materials with an integer magnetic moment of 4 mB. Densities of states, electronic band structure, and origin of ferromagnetism have been discussed, and robust HM nature of these compounds is analyzed which makes them fascinating compounds for spintronic devices.
author_names: Muhammad Atif Sattar

Muhammad Aamer Rashid

Muhammad Nasir Rasool

Asif Mahmood

Muhammad Raza-ur-rehman Hashmi

S Aftab Ahmad

Muhammad Imran

Fayyaz Hussain
title: Half Metallic Ferromagnetism in New Half Heusler Compounds: an Ab Initio Study of CrTiX (X Si, Ge, Sn, Pb)
year: 2016

abstract: Mn2 based Heusler compounds have attracted a great deal of interest as half metallic ferri and ferromagnets and as materials for spintronic applications. In this paper, we report the synthesis, crystal structure, and disorder type of the new Heusler compounds Mn2RuGe, Mn2RhGa, and the redetermination of the crystal structure of Mn2RuSn. They crystallize cubic with L21b structure type in Fmm, which is an inverse Heusler structure with a transition metal disorder of the type (Mn0.5,Y0.5)2MnZ (Y Ru or Rh and Z Ge, Ga or Sn) It is shown that an inverse Heusler structure can generally gain stability through the configurational part of the entropy of mixing at elevated temperatures without loosing too much enthalpy in the configurational part of the enthalpy of mixing owing to a special bond arrangement in the inverse type structure. The enthalpy of formation of transition metal based Heusler compounds and Al, Ga, and Ge as the main group metals obtained from DFT calculations and experimental data are used to confirm Burch's rule, which predicts the stability of transition metal based inverse Heusler compounds. Alloying tendencies as manifested in binary phase diagrams and the enthalpies obtained from the Miedema model are correlated with the stability of Heusler compounds. Burch's rule is in excellent agreement with the current available experimental data. The DFT data and general alloying tendencies show that deviations are expected from this rule. Miedema's model allows the estimation of the enthalpy of formation for the transition and main group metal based Heusler compounds, except for those having period 6 elements and Pd.
author_names: Guido Kreiner

Adel Kalache

Steffen Hausdorf

Vajiheh Alijani

J F Qian

Guangcun Shan

Ulrich Burkhardt

Siham Ouardi

Claudia Felser
title: New Mn2 based Heusler Compounds+
year: 2014

abstract: Abstract Based on the previous research and summary, a new half metallic Heusler alloy FeCrAs have been proposed. The density functional theory of spin polarization is calculated by using the first principles calculation software CASTEP to determine the lattice constants of FeCrAs compounds in half Heusler structure. The effect of each element on its half metallicity and the formation of band gap are calculated. The total magnetic moment is calculated and verified theoretically. The range of lattice distortion which keeps half metallic properties was studied to ensure its half metallic properties. In the calculation process, the role of Fe atom in the crystal cell, based on the theory of level splitting in the crystal field of the complexes, has been studied. According to the calculations, the FeCrAs compound of Half Heusler phase is a new Heusler alloy.
author_names: Zhaopeng Hao

Ran Liu

Yihang Fan

Lili Wang
title: First principles calculations of a new half metallic Heusler alloy FeCrAs
year: 2020

abstract: .i ACKNOWLEDGMENTS..iii DEDICATION .iv LIST OF TABLE..viii LIST OF FIGURES..ix CHAPTER 1 INTRODUCTION..1 1.1 Spin Polarization..3 1.2 Half Metals..5 1.3 Thesis statement..7 1.4 Thesis Outline..8 CHAPTER 2 THEORETICAL BACKGROUND..9 2.1 Heusler Compounds..9 2.2 .1 Crystal Structure of Heusler Alloys..11 2.2 X ray Diffraction for Determination of Crystal Structure..13 2.2.1 Structure Factor (F).14 vi 2.2.2 X ray Diffraction Pattern for the Order and Disorder Heusler Compounds..15 2.3 Magnetism and magnetic Properties of Heusler Compounds..18 2.4 Literature Review..21 CHAPTER 3 EXPERIMENTAL TECHNIQUES..24 3.1 Sample Preparation..24 3.2 X ray Diffraction Measurements..26 3.3 Metallography..28 3.4 Magnetization Measurements..29 CHAPTER 4 RESULTS AND DISCUSSIONS..31 4.1 Mn2CoZ Family..31 4.1.1 Mn2CoGa..31 A. The crystal structure of Mn2CoGa..31 B. The Magnetic Properties of the Mn2CoGa..36 C. The Microstructure of Mn2CoGa..40 4.1.2 Mn2CoGe and Mn2CoSb..41 4.2 Mn2FeZ Family..44 4.2.1 Mn2FeSi..44 A. The Crystal Structure of Mn2FeSi..44 B. The Microstructure of Mn2FeSi..50 4.2.2 Mn2FeGe..51 CHAPTER 5 CONCLUSION..53 REFERENCES..56
author_names: Said Bakkar
title: NEW INVERSE HEUSLER MATERIALS WITH POTENTIAL SPINTRONICS APPLICATIONS
year: 2017

abstract: Crystalline solids are characterized by periodic structures, resulting in a diverse assortment of crystal structures that exhibit a wide variety of properties. Here we report short range order, which results in characteristic diffuse bands in electron diffraction patterns, in a series of defective 19 electron half Heusler compounds for the first time. The co existence of the vacancy related short range order and the crystalline long range periodic structure makes these defective half Heusler compounds promising thermoelectric materials with low thermal conductivity and high electrical conductivity simultaneously. This new finding provides important insights into the intrinsic nature of defective HH compounds, and also proposes a possible strategy for tuning the degree of ordering to offer great potential for further improvement of thermoelectrics.
author_names: Kaiyang Xia

Pengfei Nan

Shihua Tan

Yumei Wang

Binghui Ge

Wenqing Zhang

Shashwat Anand

Xinbing Zhao

Gerald Jeffrey Snyder

Tiejun Zhu
title: Short range order in defective half Heusler thermoelectric crystals
year: 2019

abstract: Electronic structure theory has recently been used to propose hypothetical compounds in presumed crystal structures, seeking new useful functional materials. In some cases, such hypothetical materials are metastable, albeit with technologically useful long lifetimes. Yet, in other cases, suggested hypothetical compounds may be signifi cantly higher in energy than their lowest energy crystal structures or competing phases, making their synthesis and eventual device stability questionable. By way of example, the focus here is on the family of 1:1:1 compounds ABX called "fi lled tetrahedral structure" (sometimes called Half Heusler) in the four groups with octet electron count: I I VI (e.g. CuAgSe) I II V (e.g. AgMgAs) I III IV (e.g. LiAlSi) and II II IV (e.g. CaZnSn) First principles thermodynamics is used to sort the lowestenergy structure and the thermodynamic stability of the 488 unreported hypothetical ABX compounds, many of which were previously proposed to be useful technologically. It is found that as many as 235 of the 488 are unstable with respect to decomposition (hence, are unlikely to be viable technologically) whereas other 235 of the unreported compounds are predicted to be thermodynamically stable (hence, potentially interesting new materials) 18 additional materials are too close to determine. The electronic structures of these predicted stable compounds are evaluated, seeking potential new material functionalities.
author_names: Xiuwen Zhang

Liping Yu

Andriy Zakutayev

Alex Zunger
title: Sorting Stable versus Unstable Hypothetical Compounds: The Case of Multi Functional ABX Half Heusler Filled Tetrahedral Structures
year: 2012

abstract: Abstract The study of new semiconducting materials with enhanced structural, electronic, mechanical and optical properties for the advancement of optoelectronic applications has high merits in material science. First principles calculations are carried out based on density functional theory for the semiconducting Li based half Heusler compounds (X Li; Y= Be, Sc; Z As, Sb, Bi, Ge, Si) for three different atomic configurations namely a, b and g phases of C1b crystal structure. It is predicted that a phase is the lowest energy phase for LiBeAs, LiBeSb, LiBeBi and b phase for LiScGe and LiScSi. The computed electronic structure profile reveals the semiconducting behavior for these materials. The calculated elastic constants obey the necessary mechanical stability condition suggesting that all the half Heusler alloys are mechanically stable at ambient condition. Also, The study of the optical properties of these Li based compounds against the incident photon energy radiation illustrates that these materials can be the effective candidates for the optoelectronic devices. These Li based half Heusler alloys could be promising materials to use in optoelectronic and solar cell applications.
author_names: A Amudhavalli

R Rajeswarapalanichamy

K Iyakutti

Anoop Kumar Kushwaha
title: First principles study of structural and optoelectronic properties of Li based half Heusler alloys
year: 2018