Equiatomic Compounds Research Articles

Structure, physical and 27Al NMR-spectroscopic properties of the equiatomic compounds of the type REAlRh (RE = Sm, Tb, Dy, Er, and Lu)

Abstract Within the series of the equiatomic REAlRh compounds, the representatives with RE = Y, La–Nd, Gd, Ho, Tm and Yb have been synthesized. The members with RE = Sm, Tb, Dy, Er and Lu, however, had not yet been reported. They have now been synthesized and structurally as well as magnetically and NMR-spectroscopically characterized. All members crystallize isostructurally in the orthorhombic TiNiSi type, similar to most of the known analogues. The evolution of their unit cell volumes exhibits the expected decrease due to the lanthanide contraction. While LuAlRh shows Pauli-paramagnetic behavior, SmAlRh, TbAlRh, DyAlRh, ErAlRh, and TmAlRh exhibit antiferromagnetic ground states with Néel temperatures between T N = 45 and 4 K. 27Al MAS-NMR investigations have been conducted on YAlRh and LuAlRh. The results of quantum-chemical calculations support the conclusions drawn from the NMR-spectroscopic study and give information on the charge distribution in these intermetallic aluminum metallides.

Investigating Structural, Mechanical, Electronic and Magnetic Properties of Spin-Gapless Quaternary Heusler Alloy Crmnval

Utilizing density functional theory (DFT), the study thoroughly investigates the equiatomic quaternary Heusler compound CrMnVAl, revealing its promising properties across multiple domains. The energy minimization curve shows its structural stability with lattice parameter 5.91Å in ferromagnetic phase. The negative values of formation and cohesive energy indicate its chemical stability, while electronic structure analysis demonstrates spin gapless semiconducting behavior. The total spin magnetic moment of this compound is almost 3.00 μB obeying the Slater-Pauling 18 electron rule (Mt = Zt – 18). The 100% spin polarisation and the Curie temperature higher than ambient temperature indicate that this compound acts as a promising material for spin dependent applications. Furthermore, exploring its mechanical properties complements these findings, offering insights into its structural integrity and suitability for diverse applications. Overall, the study underscores CrMnVAl's potential as a versatile material for spintronics and beyond.

Structural, mechanical, electronic, magnetic, optical, and thermoelectric properties of a new equiatomic quaternary heusler compound FeZrCrZ (Z = Si, Ge, Sn): A first-principles investigation

In this investigation, we undertake an ab initio exploration of the structural, mechanical, electronic, magnetic, optical, and thermoelectric characteristics of equiatomic quaternary Heusler compounds (EQH), specifically FeZrCrZ (Z = Si, Ge, Sn). Our investigation involves the utilization of the full-potential linearized augmented plane wave method (FP-LAPW) in density functional theory (DFT) framework, employing the generalized gradient approximation (GGA). The findings reveal that the Y-type-I arrangement, demonstrating ferromagnetic alignment, emerges as the most thermodynamically favored configuration among all FeZrCrZ (Z = Si, Ge, and Sn) compounds. Computed values for formation energy substantiate the feasibility of experimental synthesis.Furthermore, we meticulously determine elastic constants, confirming the structural robustness of the quaternary compounds. Dynamic stability analysis reinforces their stability. Electronic property assessments unveil the semi-metallic nature of FeZrCrZ (Z = Si, Ge, and Sn) alloys, showcasing complete spin polarization at the Fermi energy (100 %), a minimal energy gap, and magnetic moments of 2 μB when Z = Si, Ge, and 4 μB when Z = Sn. Optical property calculations encompass complex refractive index, dielectric function, reflectivity, absorption coefficient, and optical conductivity, indicating potential suitability of these compounds for optoelectronic applications. Employing Boltzmann transport theory, we investigate the thermoelectric performance of the compounds concerning temperature, and chemical potential. Evaluation of the thermoelectric response underscores their viability as thermoelectric materials, linked to a substantial figure of merit, increased Seebeck coefficient, and diminished thermal conductivity. This study provides crucial theoretical insights for experimental researchers, offering valuable information for the synthesis and application of these compounds in spintronics, thermoelasticity, and optoelectronics.

Investigation on New Orthorhombic AuR (R = Ho, Tb, Y) and PdR (R = Eu,Gd,Y) Equiatomic Compounds’ Structural, Vibrational, and Thermal Properties

Herein, first‐principles calculations using the planewave pseudopotential technique to assess the structural, elastic, vibrational, and thermal properties of equiatomic intermetallic consisting of rare earth elements (Eu, Gd, Ho, Y, Tb) and noble metals (Au, Pd) are used. This approach involves optimizing novel orthorhombic structures by minimizing the total energy and interatomic forces. The computed structural features for the investigated intermetallics closely align with available experimental data. By evaluating stability criteria using the derived elastic constants, this analysis verifies the stability of these intermetallics in an orthorhombic structure at zero pressure. Furthermore, various mechanical parameters are determined, including (Young's E, bulk B, shear G, Pugh's) modulus, Poisson's ratio, and anisotropy factors. These parameters are derived from the computed single‐crystal elastic constants using the Voigt–Reuss–Hill average method. This investigation delves into the relationship between temperature and variations in heat capacity at constant volume (Cv) and entropy (S), comprehensively exploring these variables.

Estimation of the Lattice Parameter and Lattice Distortion Based on the Results of <i>Ab Initio</i> Study of Structural Fragments of TiVZrNbMo, TiVZrNbHf, and TiVZrNbTa Multicomponent Alloys

Isolated clusters, fragments of the bcc structure of the compounds of the TiVZrNbMo, TiVZrNbHf and TiVZrNbTa systems, have been constructed and studied from the first principles. An approach has been developed and applied to predicting the lattice parameter and its distortion in solid-state structures based on the results of an Ab initio study of fragments of their structure. It has been established that the predicted values of the lattice constant of the equiatomic compounds TiVZrNbMo, TiVZrNbTa, TiVZrNbHf agree with the available experimental values with high reliability. The developed approach, together with the constructed models of isolated clusters, can be recommended for predicting the lattice parameter and its distortion in new predictive multicomponent metalic compounds.

Large unsaturated magnetoresistance and electronic structure studies of single-crystal GdBi

Single crystal of the binary equiatomic compound GdBi crystallizing in the rock-salt-type cubic crystal structure with the space group $Fm\overline{3}m$ has been grown by flux method. The electrical and magnetic measurements have been performed on well-oriented single crystals. The antiferromagnetic ordering of the Gd moments is confirmed at ${T}_{\mathrm{N}}=27.5$ K. The magnetization measurement performed at 2 K along the principal crystallographic direction [100] attained a value of $1.3\phantom{\rule{0.16em}{0ex}}{\textmu{}}_{B}$/Gd in a field of 7 T, which is about 5 times smaller than its saturation value of $7\phantom{\rule{0.16em}{0ex}}{\textmu{}}_{B}$. Zero-field electrical resistivity reveals a sudden drop at 27.5 K, suggesting a reduction in the spin disorder scattering due to the antiferromagnetic alignment of the Gd moments. The residual resistivity at 2 K is 390 $\mathrm{n}\mathrm{\ensuremath{\Omega}}\mathrm{cm}$, suggesting a good quality of the grown crystal. The magnetoresistance attains a value of ${10}^{4}%$ with no signature of saturation, in a field of 14 T at $T=2$ K. Shubnikov--de Hass oscillations have been observed in the high field range of the magnetoresistance with three fundamental frequencies corresponding to the extremal areas of the Fermi surface. Our results suggest that the extremely large unsaturated magnetoresistance in this compound is due to near compensation of the charge carriers. We also performed angle-resolved photoelectron spectroscopy measurements with different photon energies and compared our results with the calculated band structure of GdBi.

Equiatomic intermetallic barium compounds BaTX (T=Pd, Pt, Au; X=Mg, Zn, Cd) with TiNiSi and ZrBeSi type structure

AbstractThe equiatomic ternary BaTX (T=Pd, Pt, Au; X=Mg, Zn, Cd) phases were obtained by reaction of the elements in sealed tantalum ampoules. The compounds were characterized through their X‐ray powder patterns. BaAuMg and BaTCd (T=Pd, Pt, Au) crystallize with the TiNiSi type structure, while the compounds BaTZn (T=Pd, Pt) adopt the ZrBeSi type. The structures of BaAuMg and BaPdZn were refined from single crystal X‐ray diffractometer data: Pnma, a=801.34(5), b=467.71(8), c=924.07(10) pm, wR2=0.0955, 736 F2 values, 20 variables for BaAuMg and P63/mmc, a=449.68(2), c=901.62(4) pm, wR2=0.1172, 145 F2 values, 8 variables for BaPdZn. The structures derive from the aristotype AlB2. The gold and magnesium atoms form puckered Au3Mg3 hexagons with 284–328 pm Au−Mg while the Pd3Zn3 hexagons in BaPdZn are planar (260 pm Pd−Zn). Comparison of all known BaTX phases shows a range of the valence electron count (VEC) from 13 (BaMnGe) to 18 (BaAuP). The BaTX phases crystallize with seven different structure types and there is no obvious correlation with VEC.

Experimental observation of spin glass state in the highly disordered quaternary Heusler alloy FeRuMnGa

The realization of the spin-glass (SG) state in Heusler alloys is very rare despite the presence of inherent structural and elemental disorder in those compounds. Although a few half- and full-Heusler alloys are known to exhibit the SG state, there is hardly any manifestation of the same in cases of quaternary Heusler compounds. Here we report the observation of a SG state in a highly disordered equiatomic quaternary Heusler compound: FeRuMnGa where the SG state is in between the canonical SG and the cluster glass. Different intricate features of the SG state including nonequilibrium magnetic dynamics at low temperatures in the compound are unveiled through our comprehensive magnetic, heat capacity, and neutron-diffraction studies. The structural disorder in the sample is neither conventional $A2$- nor $B2$ -type whereas those two types are commonly observed for Heusler compounds. The presence of disorder also plays a significant role in electron transport properties of the alloy, which is reflected in its exhibition of semimetallic behavior and anomalous Hall effect at low temperatures.

Large Magnetic Entropy Change in GdRuSi Optimal for Magnetocaloric Liquefaction of Nitrogen

The search for new magnetocaloric materials for application in magnetic refrigerants is highly motivated by high efficiency, reliability, and environmental safety. The values of the magnetocaloric effect MCE and the refrigerant capacity RC for the equiatomic GdRuSi compound were determined to be MCE = 10.7 and 4.94 J/kgK and RC = 336 and 92 J/kg with a change in the field of 0–50 and 0–17 kOe, respectively. These high values of MCE and RC for GdRuSi appear in the region of nitrogen liquefaction temperature of 77.4 K, due to which the compound can be useful in practice. The densities of states and magnetic moments of GdRuSi were calculated theoretically, taking into account strong electron correlations in the 4f Gd shell. The total magnetic moment of GdRuSi was found to be composed of the Gd moment only with the value calculated in very good agreement with the experimental one.

New superhard tetragonal BCN from crystal chemistry and first principles

Novel ternary equiatomic BCN compound structurally based on the ‘glitter’ C6 with both tetrahedral (sp3) and trigonal (sp2) carbons has been predicted using crystal chemistry rationale and supported by first principles calculations of energies and energy dependent quantities within density functional theory (DFT). Crystal structure of BCN belongs to the tetragonal space group P42mc and is built by stacking of corner sharing BC2N2 tetrahedra. The phase is found energetically cohesive and stable both mechanically (elastic properties) and dynamically (phonons band structures). The electronic band structures reveal metallic-like behavior. Characterized by very high Vickers hardness (65 GPa), BCN is expected to be a prospective superabrasive.

True colours shining through: Determining site distributions in coloured Li-containing quaternary Heusler compounds

The compounds LiMgPdSn, LiMgPtSn, LiMgPdGe, and LiMgCdGe were prepared by induction heating followed by annealing at 600 ​°C. The cubic structure of LiMgPdSn, which serves as the parent structure type for equiatomic quaternary Heusler compounds, was confirmed to contain an ordered site distribution (or “colouring”) by powder X-ray diffraction, 7Li solid-state nuclear magnetic resonance spectroscopy, and electronic structure calculations. The Li atoms occupy one site in LiMgPdSn, LiMgPtSn, and LiMgCdGe, but more than one site in LiMgPdGe. These compounds are rare examples of coloured metallic materials, with LiMgPdSn, LiMgPtSn, and LiMgPdGe appearing red and LiMgCdGe appearing blue. Their colours were quantified by extracting chromaticity coordinates from optical reflectance spectra. As a test of machine-learning models that propose the formation of quaternary Heusler compounds, the new compound LiMgPtZn was prepared, but other predictions were wrong.

Bulk-like first-order magnetoelastic transition in FeRh particles

Near-equiatomic, chemically-ordered iron-rhodium (FeRh) alloy is a fundamentally interesting material that may become useful in niche applications making use of its unique magneto functional phenomena, for example, the giant inverse magnetocaloric effect near room temperature that is associated with a sharp first-order magnetic phase transition. The nearly discontinuous antiferromagnetic-ferromagnetic phase transformation in bulk FeRh is well-known; however, the transition broadens considerably in fine particles and films with thickness less than 50 nm, precluding their potential applications. Here, we report an abrupt, bulk-like first-order magnetoelastic transformation in powders consisting of sub-micron particles of nearly equiatomic FeRh compound synthesized via solid-state mechanochemical co-reduction of FeF2 and RhCl3 and subsequent heat treatments. We demonstrate that annealing at temperatures ranging from 600 ̊C to 800 ̊C enables tailoring phase content, particle size, and magnetic properties of the powders. A maximum magnetic-field-induced entropy change of ~10 J/kg K at μ0ΔH = 1 T has been achieved in powders annealed at 800 ̊C. The retention of extraordinary responsiveness in sub-micron particles of FeRh is likely to open doors for system component fabrication using additive manufacturing methods, along with new opportunities to employ FeRh in theranostics.

Pressure and spin effect on the stability, electronic and mechanic properties of three equiatomic quaternary Heusler (FeVHfZ, Z = Al, Si, and Ge) compounds

In this paper, three equiatomic quaternary Heusler compounds − FeVHfZ (Z = Al, Si, and Ge) − are investigated for their structural, magnetic, electronic, mechanic, and lattice dynamic properties under pressure effect. These compounds are optimized for under three structural types and three magnetic phases: β is the most stable structure with ferromagnetic phase. The electronic properties reveal that FeVHfAl is a half-metal, and that FeVHfSi and FeVHfGe are spin gapless semiconductors. In addition to electronic band structure, possible hybridization and partial density of states are presented. Furthermore, the mechanical properties are studied, and the three-dimensional direction-dependent mechanical properties are visualized under varying pressure effects. Our results reveal the half-metal and spin gapless semiconductor nature of the ferromagnetic FeVHfZ compounds, making them promising materials for spintronics applications.

Anomalous magnetoresistance and magneto-thermal properties of the half-Heuslers, RPdSi (R = Y, Gd–Er)

Here, we present a detailed study on the magnetic, magneto-transport, and magneto-thermal properties of the equiatomic half-Heusler compounds with the general formula, RPdSi (R = Y and rare-earth, Gd–Er). These materials crystallize in two different superstructures of the TiNiSi-type orthorhombic unit cell with the space groups Pnma and Pmmn. Our magnetic and heat capacity measurements reveal the onset of an antiferromagnetic (AFM) ordering in the temperature range 3–16 K for all the local moments bearing RPdSi compounds, while the non-magnetic analog, YPdSi exhibits a Pauli-paramagnetic behaviour. The AFM state of these compounds can be tuned by magnetic field and temperature as demonstrated by the magnetic measurements below the Neel temperature (T N). Most importantly, this tuning of the magnetic structure is well documented in the complex temperature and field dependence of magnetoresistance (MR) and magnetocaloric effect (MCE). Our study establishes a striking correlation of the commensurate/incommensurate AFM structure with that of positive/negative MR and MCE in this series of compounds. We emphasize that such a framework applies to a large number of AFM intermetallic systems.

Equiatomic quaternary Heusler compounds TiVFeZ (Z=Al, Si, Ge): Half-metallic ferromagnetic materials

Equiatomic quaternary Heusler compounds (EQHCs) are very promising materials for spintronic applications due to their excellent electronic and magnetic properties. In this study, structural, electronic, magnetic, mechanic, and dynamic properties of TiVFeZ (Z=Al, Si, Ge) EQHCs are investigated. Three nonequivalent structural configurations of α, β, and γ type structures are considered. The γ is defined as the most stable phase for all these compounds and has a half-metallic character. The predicted Curie temperatures of TiVFeAl, TiVFeSi, and TiVFeGe compounds are about 488 K, 256 K, and 306 K, respectively. We also show that TiVFeZ (Z=Al, Si, Ge) have thermodynamic, dynamic, and mechanical stabilities. The presented results reveal that these compounds are potential materials for spintronics applications.

Density functional theory investigation on lattice dynamics, elastic properties and origin of vanished magnetism in Heusler compounds CoMnVZ (Z = Al, Ga)* *Project supported by Special Fund for Introduced Talent to Initiate Scientific Research in Nanjing Tech University and the National Natural Science Foundation of China (Grant Nos. 51831003 and 51771225).

The lattice dynamics, elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ (Z = Al, Ga) are investigated by first principle calculations in this work. Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds, they are both stable in LiMgPdSn-type structure with comparable lattice size, phonon dispersions and electronic structures. Comparatively, we find that CoMnVAl is more structurally stable than CoMnVGa. Meanwhile, the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness, which leads to better comprehensive mechanical properties than those of CoMnVGa. Practically and importantly, structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures. Owing to atomic preferential occupation in CoMnVAl/Ga, the localized atoms Mn occupy C (0.5, 0.5, 0.5) Wyckoff site rather than B (0.25, 0.25, 0.25) and D (0.75, 0.75, 0.75) Wyckoff sites in LiMgPdSn-type structure, which results in symmetric band filling and consequently drives them to be non-magnetic. Correspondingly, by tuning localized atoms Mn to occupy B (0.25, 0.25, 0.25) or/and D (0.75, 0.75, 0.75) Wyckoff sites in off-stoichiometric Co–Mn–V–Al/Ga compounds and keeping the total valence electrons as 24, newly compensated ferrimagnetic compounds are theoretically achieved. We hope that our work will provide more choices for spintronic applications.

Novel half-metallicity in Y-type equiatomic quaternary Heusler alloys XFeCrAl (X = Rh, Pd, and Pt)

In the present study, we performed theoretical investigations to understand the origin of the half-metallic properties of new types of equiatomic quaternary Heusler compounds XFeCrAl (X = Rh, Pd, and Pt) and their possible applications in spintronics. These compounds crystallize in the Y-type structure with the F-43m space group, where the constitutive atoms are located in their non-equivalent positions in Type-I. Furthermore, we verified the thermodynamic, chemical, mechanical, and dynamical stabilities of these alloys. The results showed that they are stable in the magnetic phase where the optimized lattice constants are X-dependent. Among the three sample alloys, PdFeCrAl was shown to be the hardest with a brittle nature, whereas the others were found to be ductile. Analyses of the energy bands and magnetic profiles indicated the 100% spin-polarized, half-metallic, ferromagnetic natures of PdFeCrAl and PtFeCrAl, with EHM values of 0.09 eV and 0.03 eV, respectively, whereas RhFeCrAl is a nearly half-metallic ferrimagnet with 91% spin-polarization and it tends to act as a half-metal under the effect of uniform pressure. Their half-metallic nature can be expected because of the wide range of uniform strain due to their high bulk moduli. Thus, they have novel characteristics with lattice constants in the ranges of 5.55–5.64 Å, 5.53–6.04 Å, and 5.55–5.99 Å for RhFeCrAl, PdFeCrAl, and PtFeCrAl, respectively. The total magnetic moments of 1.98 μB, 2.99 μB, and 3.0 μB per formula unit obtained for RhFeCrAl, PdFeCrAl, and PtFeCrAl follow the Slater–Pauling rule. The highest Curie temperature (1113 K) obtained for PtFeCrAl demonstrates its feasible applications in spintronics with a high temperature limit.

Анизотропия поверхностной энергии кубических высокоэнтропийных сплавов и покрытий

The empirical model proposed by us makes it possible to calculate the thickness of the surface of a high-entropy alloy and the anisotropy of its surface energy. Cubic equiatomic compounds with an fcc structure were taken for the study. It was found that these structures in the surface layer have an average thickness of about 2 nm, which represents 5-6 monolayers, which are confirmed by reconstruction or relaxation of the alloy surface. These structures are nanostructured formations. It turns out that the thickness of the surface of these layers is approximately the same as the thickness of the surface of amorphous metals layers. They also have approximately the same hardness of 500-800 HV, but 2-3 times higher than the hardness of stainless steels - 200-400 HV. From our point of view, there is much in common between high-entropy alloys and amorphous metals, despite the fact that the former are crystalline, and the latter are amorphous. In the proposed empirical model, it is shown that the maximum surface energy is attained in the [111] plane. It is also shown that the melting temperature of different faces becomes different and, with a decrease in the particle size, it changes according to the hyperbolic law.

Electroanalytical sensing of trace amounts of As(III) in water resources by Gold–Rare Earth alloys

Gold–Rare Earth (Au-RE, RE = Sm, Dy, Ho, Y) alloys were prepared by co-melting stoichiometric amounts of metals. XRPD and SEM/EDX analysis revealed the formation of equiatomic compounds. These alloys were used for the preparation of electrodes for As(III) sensing in aqueous samples. All four electrodes gave a clear response in the presence of As(III) in weakly alkaline media (NaHCO3 + Na2CO3 buffer). Following optimisation of operating parameters (deposition potential of −0.9 V vs SCE and deposition time of 180 s), limits of detection of As(III) at four electrodes were determined to be in 0.8–2.3 ppb region. Au-RE electrodes gave a clear response in the presence of Cu(II) as model interferent and, finally, showed the ability for As(III) sensing in a real sample.

First principles analysis of the half-metallic ferromagnetism, elastic and thermodynamic properties of equiatomic quaternary Heusler compound CoCrRhSi

In this paper, the structural, electronic, magnetic, elastic, and thermodynamic properties of the new equiatomic quaternary Heusler (EQH) compound CoCrRhSi are theoretically investigated. The ferromagnetic state is found to be energetically favorable. CoCrRhSi is a half-metallic compound exhibiting the metallic spin-up channel and a semiconducting behavior with an indirect band gap of 1.125 eV in the spin-dn channel. Moreover, the magnetic properties of this material satisfy the Slater–Pauling rule with a total magnetic moment of 4 μB. The strain effect investigation indicates that the half-metallicity is more stable under the lattice compression than the tension. Elastic properties results indicate the mechanical stability and elastic ductility of this compound. Finally, with the aim of providing thermodynamic characteristics of CoCrRhSi compound under different working conditions of pressure and temperature, its thermodynamic parameters including volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are determined and discussed in detail.