Electronic and Structural Properties of NaZnAs Compound : An Ab-Initio Study in the Tetragonal and Cubic a Phases (original) (raw)
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Electronic and structural properties of NaZnX (X = P, As, Sb): an ab initio study
Journal of Physics: Condensed Matter, 2008
The first-principles tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground-state properties, structural phase stability and pressure dependence of the band gap of NaZnX (X = P, As, Sb). All three compounds are found to crystallize in the tetragonal Cu 2 Sb-type (C38) structure. NaZnAs is also found to crystallize in the zinc-blende-type related structure, i.e. the MgAgAs (order CaF 2)-type structure. By interchanging the position of the atoms in the zinc-blende structure, three phases (α, β and γ) are formed. The energy-volume relations for these compounds have been obtained in the Cu 2 Sb-type and cubic α, β and γ phases of the zinc-blende-type related structure. Under ambient conditions these compounds are more stable in the Cu 2 Sb-type structure and are in agreement with experimental observations. At high pressure, these compounds undergo a structural phase transition from the tetragonal Cu 2 Sb-type to cubic α (or β) phase, and the transition pressures were calculated. The equilibrium lattice parameter, bulk modulus and the cohesive energy for these compounds have also been calculated and are compared with the available results. In the Cu 2 Sb-type structure, NaZnP is found to be a direct-band-gap semiconductor, NaZnAs shows a very small direct band gap and NaZnSb is found to be a metal. In the α and β phases, NaZnP is found to be a direct-band-gap semiconductor, whereas NaZnAs and NaZnSb are found to be semi-metallic. In the γ-phase, all three compounds are found to exhibit metallic behaviour. However, this phase is energetically unfavourable.
Computational Materials Science, 2014
Ab-initio full potential augmented plane wave plus local orbitals method has been used to investigate the structural phase transition, mechanical and optoelectronic properties of the Nowotny-Juza filled-tetrahedral compound NaZnP. The exchange-correlation potential was treated within the generalized gradient approximation of Perdew-Burke and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential (TB-mBJ) to improve the accuracy of the electronic band structure. Total-energy and geometry optimizations have been carried out for all structural phases of NaZnP. The following sequence of pressure-driven structural transitions has been found: Cu 2 Sb-type ? b-phase ? a-phase. The single-crystal elastic constants of NaZnP in the Cu 2 Sb-type structure have been calculated using total-energy versus strain method and their corresponding elastic moduli of polycrystalline aggregate, including Young's modulus, shear modulus and Poisson's ratio, have been derived. From the elastic parameters, it is inferred that this compound is brittle in nature. The elastic anisotropy was studied in detail using three different indexes; especially the 3D direction dependence of the Young's modulus was visually described. Furthermore, calculated electronic band structure shows that NaZnP in the Cu 2 Sb-type phase has a direct energy band gap (C-C). The TB-mBJ approximation yields larger fundamental band gaps compared to those of PBE-GGA. The examined charge density distributions for the Cu 2 Sb-type structure show a covalent character for Zn-P bond and ionic nature for Na-P bond. Additionally, real and imaginary parts of the dielectric function, reflectivity and energy loss function spectra have been calculated for radiation up to 30.0 eV with an incident radiation polarized parallel to both [1 0 0] and [0 0 1] crystalline directions.
Electronic properties and elastic constants of wurtzite, zinc-blende and rocksalt AlN
Journal of Physics and Chemistry of Solids, 2006
Electronic properties and elastic constants of AlN in the wurtzite, zinc-blende and rocksalt structures are investigated using an ab initio pseudopotential method based on the density-functional theory with both the local-density approximation and the generalized gradient approximation for the exchange-correlation functional. The numerically calculated results compare well with the existing experimental data. For elastic constants of rocksalt AlN our results are predictions.
Mechanical and electronical properties of ZnS under pressure
2008
AbstrAct Purpose: The wide-gap semiconductor materials are very important for application in the fields of optical device technology. ZnS is wide-gap semiconductor that is attractive material due to the polymorphic structural transformation and it is suitable semiconductor for applications in infrared optics, ultraviolet laser devices, electronic image display, high-density optical memory, solar cell etc. The goal is to evaluate mechanical and electrical properties of ZnS dunder pressure. Design/methodology/approach: We report ab-initio calculations of lattice constants, bulk modulus and elastic constants of the B1 (rocksalt), B3 (zincblende) and B4 (wurtzite) structures of ZnS. Ab-initio calculations are based on the density functional theory (DFT) within generalized gradient approximation (GGA) for the exchange-correlation potential. Findings: Phase transition pressures from B4 phase to B3 phase, from B3 phase to B1 phase and from B4 phase to B1 are predicted from intersection of the enthalpy-pressure data for the three phases. These results are consistent with the experimental and other theoretical calculations. Mechanical properties of ZnS under high pressure are also calculated. It is seen that the mechanical properties of ZnS under high pressure are quite different from those ambient condition. The band structure, density of states (DOS) and energy gaps are also given for B3 structure of ZnS. Research limitations/implications: The results are compared with the previous theoretical and experimental data. Originality/value: Evaluation of mechanic and electronical properties of ZnS under pressure.
arXiv (Cornell University), 2022
We present a detailed density functional theory (DFT) based calculations of the structural, elastic, lattice dynamical, thermophysical, and optoelectronic properties ternary semiconductors CaZn 2 X 2 (X = N, P, As) in this paper. The obtained lattice parameters are in excellent agreement with the experimental values and other theoretical findings. The elastic constants are calculated. These elastic constants satisfy the mechanical stability criteria. Moreover, many thermophysical parameters of these compounds are estimated, including the Debye temperature, average sound velocity, melting temperature, heat capacity, lattice thermal conductivity, etc. The comprehensive analysis of the elastic constants and moduli show that CaZn 2 X 2 (X = N, P, As) compounds possess reasonably good machinability, relatively high Vickers hardness and relatively low Debye temperature. The phonon dispersion curves and phonon density of states are investigated for the first time for the compounds CaZn 2 P 2 and CaZn 2 As 2. It is observed from the phonon dispersion curves that the bulk CaZn 2 X 2 (X = N, P, As) compounds are dynamically stable in the ground state. Electronic properties have been studied through the band structures and electronic energy density of states. HSE06 (hybrid) functional is used to estimate the band gaps accurately. The electronic band structures show that CaZn 2 N 2 and CaZn 2 As 2 possess direct band gaps while the compound CaZn 2 P 2 show indirect band gap. It is observed that the band gap decreases by changing the anion X from N to As. The bonding characters of CaZn 2 X 2 (X = N, P, As) compounds are investigated. Energy dependent optical parameters exhibit good correspondence with the electronic energy density of states features. We have thoroughly discussed the reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity and loss function of these semiconductors. The optical absorption, reflectivity spectra and the refractive index of CaZn 2 X 2 (X = N, P, As) show that the compounds hold promise to be used in optoelectronic devices.
Electronic Band Structure of InxGa1-xN under Pressure
Acta Physica Polonica A, 2007
The electronic band structures of zinc-blende In x Ga 1−x N alloys with x varying from 0.03 to 0.5 are examined within the density functional theory. The calculations, including structural optimizations, are performed by means of the full-potential linear muffin-tin-orbital and pseudopotential methods. The effects of varying the composition, x, and of applying external pressure are studied. A composition-dependent band gap bowing parameter in the range of 1.6-2 eV is obtained. A strong nonlinearity in the composition dependence of the pressure coefficient of the band gap is found.
Electronic structure and structural stability of ThGa2 under pressure: an ab initio study
Philosophical Magazine Letters, 2005
The large structural stability regime of LaAl 2 and LaAl 3 as a function of pressure is investigated by the band structure calculations using the FP-LAPW method. An earlier experimental study has revealed that there is no structural phase transition at 35and35 and 35and30 GPa for LaAl 2 and LaAl 3 , respectively. Our calculations indicate that in the density of states curve of LaAl 2 , the Fermi level (E F ) lies in a slope between bonding maxima and antibonding minima. At high pressures the E F moves slightly towards the valley, but this shifting does not affect its structural stability. In LaAl 3 , the E F falls in a flat region in the density of states and does not move even up to 33 GPa. The band dispersion curves for both the compounds show movement of bands under the influence of pressure. Some of them cross the Fermi level leading to so called Lifshitz transitions. However, it is seen that these electronic changes do not manifest into any volume anomaly in LaAl 3 under pressure. Our study clearly shows that the density of states behavior for LaAl 2 and LaAl 3 satisfies the Yamashita-Asano criterion for structural stability. The theoretical equations of state, bulk modulus and its pressure derivative values are compared with the experimental values.
Electronic and Structural Properties of Zincblende B x Ga 1−x N
Turkish journal of physics, 2008
We present structural and electronic properties of the cubic structure for different concentrations x of ternary alloy BxGa1−xN. The computational method is based on the full-potential linearised augmented plane wave method (FP-LAPW). The exchange and correlation energy is described in the local density approximation (LDA) and generalized gradient approximation (GGA). We have investigated the effect of composition on the ground state properties, lattice parameters, bulk modulus, pressure derivative and band gap of the zinc blend BN and GaN. The results obtained are in a good agreement with experimental and theoretical values concerning the variation of the gaps and crossover direct, indirect band gap and the bowing parameter. A reasonable agreement is found from the comparison of our results with other theoretical calculations.
Journal of the American Ceramic Society, 2014
A systematic first-principles investigation, by using the density functional formalism with the nonlocal B3LYP approximation including a long-range dispersion correction, has been performed to calculate the structural and electronic properties and phase transitions under pressure of the three phases of ZnS (cubic zinc blende, ZB, hexagonal wurtzite, W, and cubic rock salt, RS). Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for the ZnS phases. The band structures, energy gap, density of states, and vibrational frequencies and their pressure dependences are investigated. The present results illustrate that both phases, W and ZB, present very similar enthalpy and the RS phase becomes thermodynamically more stable than ZB and W structures at 15.0 and 15.5 GPa, respectively. These phase transitions are accompanied by an increase of the first shell coordination number of Zn atom and by a cell volume collapse of 13.9% and 14.3% for ZB and W phases, respectively. The atomic contributions of the conduction and valence bands, as well the binding energy for the Zn 3d orbital have been obtained.