Structural, electronic and optical properties of the wide-gap Zn1-xCdxTe ternary alloys

International audienceThe II-VI compounds CdTe and ZnTe form a complete series of solid solutions with a cubic Zinc Blende structure. The room temperature band gap of these materials can be tuned from 1.5 eV in CdTe to 2.3 eV in ZnTe by controlling the alloy composition. This material is used as the window layer in thin-film solar cells. Using first-principles calculations, we investigated the structural and electronic properties of two binary CdTe and ZnTe for several compositions with various ordered structures (Cu3Au, luzonite) of Zn1-xCdxTe alloys using the theory of order-disorder transformation. An investigation was also conducted using the first-principles total-energy formalism based on the hybrid full potential augmented plane wave plus local orbital (APW + lo) method, within the local-density approximation (LDA) for the exchange and correlation potential. The 3d orbitals of the Zn atoms and 4d orbitals of the Cd atoms were treated as valence bands in every case. We analyzed the effect of alloying a small amount of ZnTe with CdTe; the fundamental direct band gap energy of the alloys was found to decrease per atomic percent of cadmium

Strain Control of the Tunable Physical Nature of a Newly Designed Quaternary Spintronic Heusler Compound ScFeRhP

Recently, an increasing number of rare-earth-based equiatomic quaternary compounds have been reported as promising novel spintronic materials. The rare-earth-based equiatomic quaternary compounds can be magnetic semiconductors (MSs), spin-gapless semiconductors (SGSs), and half-metals (HMs). Using first-principle calculations, we investigated the crystal structure, density of states, band structure, and magnetic properties of a new rare-earth-based equiatomic quaternary Heusler (EQH) compound, ScFeRhP. The results demonstrated that ScFeRhP is a HM at its equilibrium lattice constant, with a total magnetic moment per unit cell of 1 μB. Furthermore, upon introduction of a uniform strain, the physical state of this compound changes with the following transitions: non-magnetic-semiconductor-(NMS) → MS → SGS → HM → metal. We believe that these results will inspire further studies on other rare-earth-based EQH compounds for spintronic applications

Origin of ferromagnetism in the half‐Heusler XRbCs compounds (X=N, P and As)

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Electronic and Thermoelectric Properties of Li-Based Half-Heusler Alloys: A DFT Study

In this paper, we have studied the electronic, elastic and thermoelectric properties of the half-Heusler LiCrZ (Z = C, N, Si, and P) materials in Type II phase, in this structure the atomic occupations are X (1/2,1/2,1/2), Y (0,0,0) and Z(1/4,1/4,1/4). The ferromagnetic state of Type II structure was found to be the most stable phase for all studied alloys. After calculating the elastic constants, we found out that the conditions of mechanical stability were verified only for LiCrSi and LiCrP alloys in Type II phase, at both equilibrium a0 and half metallic ahm lattice constants, which indicates that these two compounds can be synthesized experimentally. We should also mention that the half metallic behavior in Type II structure, for LiCrSi and LiCrP compounds, was obtained by straining the equilibrium lattice constants by 2% and 6%, respectively. At ahm, these two systems were identified to be true half metals due to their complete spin polarization and integer value of total magnetic moment. These last ones have reached 3μB per unit cell when Z = Si, and 4μB when Z = P. Using the mean field approximation (MFA), the Curie temperatures of Type II structure were also determined, where the values are estimated to be 456.2 K and 302.8 K, respectively. Finally, the thermoelectric performance has been explored by the classical Boltzmann theory. At low temperatures, the figure of merit has reached 0.73 and 0.93 for LiCrSi and LiCrP, respectively. The considerable ZT values and all calculated physical properties make these two systems promising candidates for thermoelectric applications

First-Principles Investigation of Equiatomic Quaternary Heusler Alloys NbVMnAl and NbFeCrAl and a Discussion of the Generalized Electron-Filling Rule

Plane-wave pseudo-potential methods based on density functional theory are used to study the electronic structures, magnetic, and half-metallic properties of the equiatomic quaternary Heusler alloys NbVMnAl and NbFeCrAl. Calculated results reveal that NbVMnAl and NbFeCrAl alloys are newly designed half-metallic ferrimagnets with a total magnetic moment (M t ) of 2 μ B. We found that the Slater-Pauling rule, i.e., the relationship between the M t and the total number of valence electrons (Z t ) of these two alloys was different. For NbVMnAl alloy, it obeys the M t = |Z t − 18| rule. For NbFeCrAl, it satisfies the M t = |Z t − 24| rule. Also, we observed that the half-metallic band gap (HM-BG) of these two alloys was different. Namely, for one material (NbFeCrAl), it is located in the spin-up channel, and in the other (NbVMnAl), it is located in the spin-down channel. To explain these phenomena, in this work, the generalized electron-filling rule was investigated, and the origin of the HM-BG of NbVMnAl and NbFeCrAl was studied. We hope that our work may provide theoretical guidance in searching for Nb-based equiatomic quaternary Heusler half-metals in the future

Ab‐initio study of half‐metallic ferromagnetism in the XCsSr (X=C, Si, Ge, and Sn) half‐Heusler compounds

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Theoretical Study of the Electronic Properties of X2YZ (X = Fe, Co; Y = Zr, Mo; Z = Ge, Sb) Ternary Heusler: Abinitio Study

In the purpose of exploring new Heusler alloys with different magnetic applications, we have employed first principles calculations method within density functional theory. After checking the structural stability of X2YZ Heusler alloys (X = Fe, Co; Y =Zr, Mo and Z = Ge, Sb), we found that Cu2MnAl type structure is more favorable for most compounds except for X2MoGe and Co2MoSb, were the Hg2CuTi structure is energetically more stable. The trends in magnetic and electronic structures can be predicted by the structure types as well as the different kinds of hybridizations between the constituents. Among the two series only two compounds were identified to be true half metals with potential applications in spintronic devices. While one compound was classified as a nonmagnetic semiconductor with a small band gap. For the rest of materials, we found that the metallic behavior is dominant. These materials show possible interesting features in technical applications as well. The effect of distortion on the magnetic properties of Co2ZrGe and Fe2ZrSb showed that the half metallic character was preserved within a moderate range of volume changes, which makes it possible to grow these materials as thin films with modern techniques