Search

We have studied hydrostatic pressure dependence of the electronic, optical, thermodynamic and thermoelectric properties of CsVO3 via first principles calculations. In addition, temperature dependence of the thermoelectric and thermal parameters was investigated. The calculated equilibrium structural parameters are in excellent agreement with the available experimental counterparts. The calculated phonon-band dispersion curve confirms the dynamic stability of CsVO3 compound in its ground-state. Analysis of the energy band dispersion calculated within the TB-mBJ potential reveals that CsVO3 is a direct bandgap semiconductor with a fundamental bandgap of 3.14 eV. It is found that the bandgap increases with increasing pressure. Analysis of the DOS diagrams and charge density topology shows that the V-O bond is partially covalent and the Cs-O bond is predominantly ionic in nature. Frequency-dependent linear macroscopic optical coefficients, namely absorption coefficient, refractive index, extinction coefficient, reflectivity and optical conductivity, were deduced from the calculated real and imaginary parts of the complex dielectric function under hydrostatic pressure effect. The semi-classic Boltzmann transport theory was used to explore pressure and temperature dependencies of the thermoelectric properties. Pressure and temperature dependencies of the thermal parameters, viz., isochore and isobar heat capacities, lattice thermal conductivity, volume thermal expansion coefficient and Debye temperature, were explored through the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

We used first-principles electronic structure calculations to investigate the structural, elastic, electronic and optical properties of the already synthesised NaAlSe2 and NaAlTe2 tetragonal compounds and the predicted NaAlO2 and NaAlS2 tetragonal systems. The computed structural parameters using the GGA-PBE approach are consistent with the corresponding experimentally determined ones. The calculated single-crystal and polycrystalline elastic moduli show that the studied materials are mechanically stable and of a weak stiffness with strong elastic anisotropy. Calculated band structures reveal that NaAlO2, NaAlS2 and NaAlSe2 are semiconductors with an indirect bandgap of Z-Γ type, while NaAlTe2 is of a direct bandgap of Z-Z type. The calculated frequency-dependent linear optical functions show that the title compounds are characterised by significant optical anisotropy and high optical absorption for a wide photon energy range in the UV spectrum. [ABSTRACT FROM AUTHOR]

We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn2P2 layered Zintl phase at two fixed temperatures: T = 600 and 900 K through first-principles electronic band structure calculations combined with Boltzmann's transport theory within charge-carrier relaxation time and rigid band approximations. The band structure calculated using the Tran-Blaha modified Becke–Johnson potential shows a fundamental indirect energy band gap (Eg) of 1.10 eV that comes from the polyanion (In2P2)−2. CaIn2P2 exhibit a mixture of flat and dispersive energy bands in the energy window from − E g / 2 to E g / 2 eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn2P2 is equal to 1.34 W m − 1 K − 1 at 900 K and 0.70 W m − 1 K − 1 at 1250 K. This relatively low lattice thermal conductivity of CaIn2P2 can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn2P2, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of 6.0 × 10 19 c m − 3 ( 1.5 × 10 19 c m − 3 ) at 900 K. [ABSTRACT FROM AUTHOR]

First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable. [ABSTRACT FROM AUTHOR]

We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydridesA2RuH6(A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of theA2RuH6systems looking for trends on different properties as a function of theAsublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg2RuH6, Ca2RuH6, Sr2RuH6and Ba2RuH6, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist ofdorbitals of the Ru atoms, classifying these materials asd-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time. [ABSTRACT FROM AUTHOR]

The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN2are investigated in detail using theab initioplane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN2are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN2is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN2. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material. [ABSTRACT FROM AUTHOR]