Heusler materials, initially discovered by fritz heusler more than a century ago, have grown into a family of more than compounds, synthesized from combinations of more than 40 elements. Semiconducting half heusler based compounds and heterostructures grown by molecular beam epitaxy. Halfheusler alloys as promising thermoelectric materials by. Heusler thermoelectric module with high conversion. Pdf recent advances in nanostructured thermoelectric half. Unveiling the phonon scattering mechanisms in halfheusler. Half heusler compounds space group fm3m has garnered increasing attention in recent years in the thermoelectric community. Recent progress in halfheusler thermoelectric materials. Hh compounds are now considered one of the few practical high zt materials, along with skutterudite and chalcogenide compounds. Improving the thermoelectric properties of half heusler. Additionally, an inverse design by computational methods considering special requirements, e. The stabilities of the structures of bxga x be, mg, and ca are.
Hall effect have been foreseen for half heusler compounds. Thermoelectric properties of ti,zr,hfcosb type halfheusler. We report the experimental realization of this compound and the characterizations of its thermoelectric properties. Pdf recent advances in nanostructured thermoelectric. Jul 23, 2018 in this paper, we consider magnetic lanthanide half heusler compounds formed from rptbi, where r is a lanthanide or y. Heusler compounds can be made as half metals, showing a high spin polarization of the conduction electrons of up to 100% 1. Using firstprinciples calculations within density functional theory, we explore the feasibility of converting ternary half heusler compounds into a new class of threedimensional topological insulators 3dti. Electronic and thermoelectric properties of halfheusler alloys. Giant anomalous hall and nernst effect in magnetic cubic. Too much attention has been paid to the search of highzt thermoelectric materials, and the one with zt 5 has been reported recently. This report presents ab initio calculations of electronic and thermoelectric properties of the most. Many of these compounds exhibit properties relevant to spintronics, such as magnetoresistance, variations of the hall effect, ferro, antiferro, and ferrimagnetism, half and. Heusler compounds are magnetic intermetallics with facecentered cubic crystal structure and a composition of xyz half heuslers or x 2 yz fullheuslers, where x and y are transition metals and z is in the pblock. One of the best studied systems of half metals are the half heusler compounds xyz exemplified by mnnisb 1.
For halfmetallic heusler compounds the total spin magnetic moment mt scales linearly with the number. For three compounds the ferromagnetic state is more favorable than the paramagnetic state. May 30, 2010 topological insulators have been predicted and recently demonstrated experimentally in a series of binary alloys. Effect of ti substitution on the thermoelectric properties of zr,hfnisn half heusler compounds, appl. Heusler compounds include half metallic ferri and ferromagnetic materials, shape memory alloys, topological insulators, high potential magnetocalorics, and materials for spintronic applications. First principle study of structural, electronic, elastic. The improvement comes from a simultaneous increase in the seebeck. However, the design of unconventional semiconductors based on 18 for half heusler compounds or 24 valence electrons for heusler compounds is also possible, resulting in band gap widths of more than 1 ev. Heusler compounds mgagas structure type, also called semi heusler or juzanowotny compounds 5, with almost 150 distinct compounds reported in the inorganic crystal structural database icsd 6. Pdf theory of heusler and fullheusler compounds semantic. Half heusler alloys have composition xyz, whereas in the full heusler structure, the vacancies are filled in with a second atom y2site, making the composition xy 2 z 7 figure 4.
Thermoelectric properties of spark plasma sintered composites based on tinisn half. Band structure and transport studies of half heusler compound. The compositions of heusler compounds are represented by the chemical formula x 2yz for full heusler compounds and xyz for hh compounds, respectively, where x and y are metals, and z is a main group element. However, there are yet to be any reports of 100% spin polarisation experimentally. The competitiveness of half heusler compounds among the mentioned material classes, coupled. Slaterpauling behavior and origin of the halfmetallicity of. Energies 2020, 1459 4 of 11 of three binary intermetallics, namely, snv3, co2sn, and co3v, in addition to the nonstoichiometry covsn half heusler alloy. Structural, electronic and magnetic properties of x2yz. Heusler hh compounds are important high temperature thermoelectric te materials and have attracted considerable attention in the recent years.
In recent screening calculation of thermoelectric properties of 15 half heusler compounds for potential thermoelectrics, 15 half heusler compounds with highest eff values were reported, their eff without soc range from 0. These properties depend on the number of valence electrons per formula unit allowing tuning of properties through composition and alloying. Topological electronic structure in halfheusler topological. Heusler compounds makes these materials good candidates for discovering new physics and. High band degeneracy contributes to high thermoelectric. Half heusler compound by the nanocomposite approach an enhancement in the dimensionless thermoelectric. Halfheusler ternary compounds as new multifunctional. Recent advances in thermoelectric performance of halfheusler. The structural, electronic and magnetic properties of halfheusler compounds xvsb x fe, co and ni are in vestigated by using the density functional theory. Covalent bonding and the nature of band gaps in some half. Heusler compounds are a large group of intermetallic compounds with over members with similar crystal structures having a vast array of tunable properties.
The next set of systems studied was inverse heusler compounds. Pdf half heusler compounds are an impressive class of materials with a huge potential for different applications such as future energy. This compound shares the half heusler lattice with sites a and b occupied by mg atoms. The eff of xirsbx ti, zr and hf compounds without soc. Stable heusler compounds can form in many compositions 1218. The compounds are semiconductors with band gaps of about 0. Experimentally, the pristine tacosn exhibits a low lattice thermal conductivity of. G6g8 and gaps of the lnyz heusler family calculated with fully relativistic linear muffin orbitals method vs.
Introduction the heusler compounds 1 are ternary intermetallics with a 2. Effects of partial substitution of ni by pd on the. Experimental realization of heavily pdoped halfheusler. Electronic structure and physical properties of heusler compounds. Heusler compounds can be made as half metals, showing a johannes gutenberg high spin polarization of the conduction electrons of up to 100% 1. The felectronbased rareearth ternary half heusler compound dypdbi has its f energy levels located close to the fermi energy level. Pdf halfheusler compounds are an impressive class of materials with a huge potential for different applications such as future energy. Half heuslers with formula abx have the cubic mgagas type structure, forming three interpenetrating facecenteredcubic fcc sublattices and one vacant sublattice 22. The latter compounds are often called half or semi heusler alloys, while the l21 compounds are referred to as full heusler alloys. Jun 05, 2020 in summary, we have investigated the ahe, ane, and moke of all the stable magnetic cubic full heusler compounds given in the heusler database of the university of alabama 38. Enhancement in thermoelectric figureofmerit of an ntype. We give the hamiltonians both for the extended system and for slabs with 111and100surfaces.
The electronic structures and electrical transport properties are studied using ab initio calculations and the boltzmann transport equation under the. Recent advances in thermoelectric performance of half. Structural stability of nicontaining halfheusler compounds. Thermoelectric performance of half heusler compounds tinisn and ticosb, appl. Half heusler hh compounds are among the most promising thermoelectric te materials for largescale applications due to their superior properties such as high power factor, excellent mechanical and thermal reliability, and nontoxicity.
Electronic structure and thermoelectric properties of hfrhzz. Zrnisnbased half heusler compounds are a subset of a much larger family of compounds possessing the cubic mgagastype structure, which has the space groupf. Semiconducting and half metallic heusler compounds for. In native states, these half heusler compounds are identified as being topologically nontrivial semimetals, or nontrivial metals, or trivial insulators, which can be turned into insulating thin films on suitable substrates.
However, the electronic structure of these compounds. Compounds with eight valence electrons per formula unit are closely related to classical semiconductors, such as silicon and gaas. Half heusler compounds stuffed zns are candidates for thermoelectric applications and for diluted semiconductors nanostructured heuslers are need for low thermoconductivity heusler compounds are half metals with high curie temperatures. Half heusler compounds are recognized as promising thermoelectric materials for hightemperature power generation, but their relatively high lattice thermal conductivity impedes further improvement of zt. Half heusler alloys as promising thermoelectric materials by alexander a. These compounds straddle the border between topologically trivial and nontrivial electronic structures because of a strong tuning of the s and p like band inversion via atomic. The increasing interest in heusler and halfheusler compounds, since the first discovery of the 1 st cu 2 mnal heusler compound by the german scientist friedrich heusler in 1903, passing 100,000 publications in 2017, with more than 1500 reported compounds, is due to their high potential for a wide variety of applications in future energy fields. Therefore, a half heusler abx phase where a and b are typically transition metal elements, such as ti, zr. Systematic understanding of halfmetallicity of ternary. A characteristic of the half heusler type ordered structure is the vacancy site that occupies onefourth of all the lattice points. Heusler compounds scagc, ycuc, caznc, naago, and licus are studied by density functional theory for potential applications in multi. Despite the small contrast of mass between sb and sn 121. Finding unprecedentedly lowthermalconductivity halfheusler. Basics and prospective of magnetic heusler compounds.
Half heusler compounds are excellent thermoelectric materials. Today, half heusler hh compounds have emerged as promising thermoelectric materials in the intermediate temperature range 400800oc. Tunable eg orbital occupancy in heusler compounds for. Half heusler compounds containing ni of the form nimp, where m is a trivalent sc. Thermal conductivity of halfheusler compounds from. Whangbo and coworkers pointed out that the 18 electron half heusler compounds must.
Therefore, a half heusler abx phase where a and b are typically transition metal. Impurity tracking enables synthesis of tife1xnixsb half. The actual compositions of 17electron and 19electron hh systems tend to me nonstoichiometric compounds with intrinsic excess interstitial y atoms partly occupied vacantsite and xsite partly occupied vacancies, respectively. Hence, the half metallic heusler compounds are promising materials for magnetoplasmonic applications. Observation of dirac state in halfheusler material yptbi nature. The thermoelectric materials with high values of the dimensionless figure of merit zt are among the most important new energy resources. We demonstrate that the electronic structure of unstrained laptbi as a prototype system exhibits a distinct bandinversion feature. Anomalous hall effect in weyl semimetal halfheusler. Here, we report the synthesis of a new half heusler compound tacosn with a low thermal conductivity. Pdf searching for hexagonal analogues of the halfmetallic. Heusler compounds are a remarkable class of intermetallic materials with 1. Page a dissertation submitted in partial fulfillment of the requirements for the degree of doctor of philosophy physics in the university of michigan. To date, half heusler compounds have clearly surpassed nanosige in the temperature range above 800 k.
Their only drawback is the remaininghigh lattice thermal conductivity. Heusler compounds have been predicted to be half metallic possessing integer magnetic moments due to complete spin polarisation at the fermi level, a property highly desirable in spintronics. Three decades ago, refractory rnisn half heusler compounds r represents refractory metals such as hf, zr, ti were found to be narrowgap semiconductors with large seebeck coefficients in 100s of microvolt per kelvin. It is now show theoretically that ternary half heusler alloys have electronic. Ordered structures and thermoelectric properties of mnisn. The calculated formation enthalpies indicate that these materials are thermodynamically stable. Heusler hh compounds, selected from more than 100 hhs, is carried out in this paper. These compounds have an inversion asymme tic crystal structure space group no.
The large family of ternary half heusler compounds is a prime candidate for combining topological and symmetrybreaking phases to explore new collective behavior. Half heusler hh alloys have attracted considerable interest as promising thermoelectric te materials in the temperature range around 700 k and above, which is close to the temperature range of most industrial waste heat sources. For cross validation, we also fully compute the anharmonic force constants of 32 half heusler systems. Halfheusler alloys as promising thermoelectric materials. Halfmetallic ferrimagnetism in hypothetical heusler. Ordered structures and thermoelectric properties of mnisn m. Heusler compounds are among the best known intermetallic compounds.
Computational investigation of heusler compounds for. Thermoelectric property study of nanostructured ptype half heuslers hf,zr,ticosb 0. Systematic understanding of half metallicity of ternary compounds in heusler and inverse heusler structures with 3d and 4d elements. These materials are exceptionally well suited for applications in magnetic tunnel junctions acting, for example, as sensors for magnetic. Although half heusler alloys like nimnsb have attracted a lot of interest, the second family of heusler compounds, the socalled full heusler alloys, have been studied much more extensively due to the existence of diverse magnetic phenomena,11,12 mainly the transition from a ferromagnetic phase to an antiferromagnetic one by changing the concen. Half heusler hh compounds are among the most promising thermoelectric te materials for largescale applications due to their superior properties such as high power factor, excellent mechanical. Jun 27, 2020 huge attention has been shifted to thermoelectric properties of half heusler compounds because of the ability of these compounds to convert heat into electricity.
The two structures are closely related with vacant cite. Semiconducting halfheusler based compounds and heterostructures grown by molecular beam epitaxy. One of the most exotic settings for small gap insulators is among materials made entirely of metals, i. Electronic structure and thermoelectric properties of. Therefore, the synthesized compound was shown to be a multiphase. Simple rules for the understanding of heusler compounds. By analogy with the hgtecdte quantum well structure,7 topological insulators and a spin quantum. Calculated electronic and magnetic properties of the half. The calculations of thermoelectric properties of these compounds are necessitated by the search for alternatives to fossil fuel. Whangbo and coworkers pointed out that the 18 electron half heusler compounds must be nonmagnetic and semiconducting. Finally, we point out directions for further development. Rptbi is composed of three interpenetrating fcc lattices fig. Crystal structure, composition and heat treatment were found. Pdf electronic correlations in the semiconducting half.
Xyz halfheusler compounds exhibit only one magnetic sublattice since only the atoms on the octahedral sites carry a. C1b structure can be obtained from l21 one by replacing the half of. To understand the highzt behavior, we studied electronic properties of bxga x be, mg, and ca with firstprinciples calculations based on the density functional theory. Improving the thermoelectric properties of half heusler compounds. The past few years have seen nanostructuing play an important role in significantly enhancing the te performance of several hh alloys. Since the chemistry of half heusler compounds can be conveniently modified, selective doping of the three sublattices in the crystal structure can be carried out. Apr 01, 2016 structure and properties of half heusler compounds the potential of half heusler alloys for high temperature thermoelectric power generation has been discussed 6, 7. Nonetheless, it was demonstrated in the early 1990s that a subset of the half heusler compounds, with the generic formula rnx r,n are transition metal elements, and x is a main group element, display semiconducting transport while infrared absorption experiments. Similar analogies can be drawn for systems such as rutile cro2 19, 20. Extensive experimental studies showed that the majority of heusler compounds order ferromagnetically in stoichiometric composition.
New mn2based heusler compounds mn2based heusler compounds have attracted a great deal of interest as half metallic ferri and. Our results show that the z 2 topological order is due to a single band inversion at the. Stateoftheart te figure of merit of half heusler materials. Remarkably high thermoelectric efficiencies of the half. Iii,wepresentanddiscussour results for the bulk and the surface, for the a 1 and t 2 pairing states. Srikrishna ghosh1 and subhradip ghosh1, 1department of physics, indian institute of technology guwahati, guwahati781039, assam, india.
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