S. Bagci

Structural, electronic, optical, vibrational and transport properties of CuBX2 (X = S, Se, Te) chalcopyrites

The structural, electronic and optical properties of CuBX2 (X = S, Se, Te) chalcopyrite semiconductors have been studied using the full-potential (linearized) augmented plane-wave (FP(L)APW) method based on the density functional theory (DFT) within the Yukawa screened-PBE0 (YS-PBE0) hybrid functional as implemented in the WIEN2k package. We have found that our calculated structural and electronic parameters such as lattice parameter, tetragonal ratio, anion displacement and energy band gap are in very good agreement with previous experimental results. We have also presented the real and imaginary parts of the dielectric function, refractive index and absorption coefficients to describe optical properties of the investigated chalcopyrite semiconductors. Furthermore, the phonon dispersion curves and corresponding density of states have been studied by using a linear response approach based on the density functional perturbation theory implemented in the Quantum ESPRESSO code. Finally, transport properties such as the Seebeck coefficient, thermal and electrical conductivity and the figure of merit for these materials have been calculated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code.

Structural, mechanical, electronic and optical properties of BBi, BP and their ternary alloys BBi1−x P x

The ground state properties of BBi, BP and their ternary alloys BBi1−x P x are reported using first-principles calculations based on density functional theory (DFT). The modified Becke–Johnson (mBJ) potential together with the generalized gradient approximation (GGA) for the correlation potential has been used here as it is a superior method for estimating band inversion strength and band order. The zincblende phase is found to be more stable than the other phases for all studied materials. The calculated lattice constants exhibit a small deviation from the linear Vegards law with a downward bowing value of 0.11 A. The calculated ground state parameters for the studied binary compounds agree with available theoretical and experimental results. The bandgap value of the studied materials calculated with the mBJ potential is considerably enhanced with respect to values from the GGA functional. Optical properties have been calculated and analysed with photon incident energy up to 21.0 eV. The spin–orbit interaction (SOI) has also been considered for structural and electronic calculations and the results are compared with those of non-SOI calculations. The real and imaginary parts of the dielectric function have also been calculated and discussed.

Structural and electronic properties of InNxP1-x alloy in full range (0 ≤ x ≤1)

Abstract We have performed first-principles method to investigate structural and electronic properties of InNxP1−x ternary semiconductor alloy in full range (0 ≤ x ≤ 1) using density functional theory. We have used modified Becke–Johnson potential to obtain accurate band gap results. From the electronic band structure calculation we have found that InNxP1−x become metal between 47 and 80% of nitrogen concentration. Additional to our band gap calculations, we have also used the band anticrossing model. The band anticrossing model supplies a simple, analytical expression to calculate the physical properties, such as the electronic and optical properties, of III-NxV1−x alloys. The knowledge of the electron density of states is required to understand and clarify some properties of materials such as the band structures, bonding character and dielectric function. In order to have a deeper understanding of these properties of the studied materials, the total and partial density of states has been calculated. Finally, we have calculated the total bowing parameter b of studied alloys, together with three contributions bVD, bCE, and bSR due to volume deformation, different atomic electron negativities and structural relaxation, respectively.

Dielectric, humidity behavior and conductivity mechanism of Mn0.2Ni0.3Zn0.5Fe2O4 ferrite prepared by co-precipitation method

Mn–Ni–Zn ferrite with the chemical formula of Mn0.2Ni0.3Zn0.5Fe2O4 was prepared by co-precipitation method. The X-ray diffraction (XRD) results show that the prepared sample crystallizes in the cubic spinel structure with the space group of Fm3m. The morphological analysis of the sample was investigated by scanning electron microscopy (SEM). The dielectric properties of Mn0.2Ni0.3Zn0.5Fe2O4 ferrite were studied in a frequency range from 20xa0Hz to 10xa0MHz and at a temperature range from 293 to 733xa0K. The dielectric constant decreases with the increasing frequency for all the temperature values chosen. The AC conductivity mechanism was found the small polaron type of conductivity, and in addition to that, the DC conductivity can be explained by Arrhenius type conductivity. According to the dielectric results, relaxation process fits Cole–Cole model. Finally, the effect of the relative humidity upon the impedance of the sample was discussed for a frequency range between 20xa0Hz and 10xa0MHz. It is found that the impedance values decrease almost linearly with the increasing % RH (relative humidity) values at low frequencies, while the impedance of the sample is independent of % RH at high frequencies.