Aytac Erkisi

Electronic structure and magnetic properties of PbMO3 (M = Fe, Co, Ni) magnetic perovskites: An ab initio study

We present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO3 (M = Fe, Co, Ni) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. On-site Coulomb interaction is also included in calculations (LSDA+U). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (Ueff = 0). However, the inclusion of on-site Coulomb interaction (Ueff = 7 eV) opens a semiconducting gap for majority spin channel of PbFeO3 and of PbNiO3 resulting in a half-metallic character. PbCoO3 system remains as metallic with LSDA+U scheme. Bonding features of all structures are largely determined by the hybridizations between O–p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO3 is enhanced by inclusion of Hubbard-U interaction (2.55 μB ⇒ 3.78 μB). Total magnetic moments of half-metallic PbFeO3 and of PbNiO3 compounds are very close to integer values.

The Investigation of Electronic, Elastic and Vibrational Properties of an Interlanthanide Perovskite: PrYbO3

The structural, mechanical, electronic and lattice dynamical properties of the PrYbO3 compound from the ABO3-type perovskite family have been investigated by performing the first-principles density functional theory calculations using the generalized-gradient approximation (GGA) with corrected Coulomb interactions (GGA+U). Structural parameters, formation energies and phase transition pressures for the five possible phases of this compound have been calculated. Then, the spin-dependent electronic band structure and corresponding density of states (DOS) have been plotted. Also, the shear modulus, Young’s modulus, Poisson’s ratio, G/B ratio, hardness and anisotropy factors have been calculated to investigate mechanical behavior of this material. Furthermore, the phonon dispersion curves have also been plotted as corresponding phonon PDOS. According to our calculations, the orthorhombic phase of the five phases of PrYbO3 is the most stable one and exhibits a half-metallic character, which can therefore be a candidate for spintronic applications.

First-principles investigation of LaGaO3 and LaInO3 lanthanum perovskite oxides

Abstract Among the class of ABO3-type perovskite oxides, LaMO3 (M=Ga and In) compounds are investigated in cubic (Pm-3m), tetragonal (P4mm), hexagonal (P-3m1), rhombohedral (R-3c) and orthorhombic (Pbnm) phases using generalised gradient approximation (GGA) within the density functional theory. On-site Coulomb interaction is also included in the calculations (GGA + U). After the determination of the stable phase, phase transition pressures have also been calculated. Then, their full structural, mechanical, electronic, optical and vibrational properties have been studied in stable orthorhombic (Pbnm) phase. Both compounds are non-magnetic insulators in their ground states. The energy gaps (Eg) of LaGaO3 and LaInO3 compounds have been found as 3.14 and 2.55 eV, respectively. The calculated elastic constants and phonon dispersion curves confirm the stability of orthorhombic phase mechanically and dynamically.

An ab initio study on the structural, electronic and mechanical properties of quaternary full-Heusler alloys FeMnCrSn and FeMnCrSb

ABSTRACT The quaternary full Heusler alloys FeMnCrSn and FeMnCrSb, which have face-centred cubic (FCC) crystal structure and conform to space group with 216 space number, have been investigated using Generalised Gradient Approximation (GGA) in the Density Functional Theory (DFT) as implemented in VASP (Vienna Ab initio Simulation Package) software. These alloys are considered in ferromagnetic (FM) order. After the investigation of structural stability of these alloys, their mechanical and thermal properties and also electronic band structures have been examined. The calculated spin-polarised electronic band structures and total electronic density of states (DOS) within GGA approximation show that these alloys can exhibit both metallic and half-metallic characters in different structural phases. The calculated formation enthalpies and the plotted energy-volume graphs show that Type-III phase is most stable structural phase for these materials. Also, FeMnCrSb alloy in Type-I/Type-III phases and FeMnCrSn alloy in Type-III phase show half-metallic behaviour with integer total magnetic moments almost 2 and 1 μ B per formula unit, respectively, since there are band gaps observed in spin-down states, whereas they have metallic behaviour in majority bands. Other structural phases of both systems are also metallic. Moreover, the calculated elastic constants and the estimated anisotropy shear factors indicate that these materials are stable mechanically in all of three phases except FeMnCrSn in Type-I phase that does not satisfy Born stability criteria in this phase and have high anisotropic behaviour.

The investigation of electronic, mechanical and lattice dynamical properties of PdCoX (X = Si and Ge) half-Heusler metallics in α, β and γ structural phases: an ab initio study

Abstract PdCoX (X = Si and Ge) alloys which are XYZ type half-Heusler alloys and also have face centred cubic MgAgAs-type structure which conforms to space group, have been investigated in different atomic arrangements which are called α, β and γ phases, using local spin density approximation in the density functional theory as implemented in VASP (Vienna Ab Initio Simulation Package) software. Both of the alloys are considered in ferromagnetic order. After the investigation of stable structural phase for these alloys, their full structural, electronic, magnetic, mechanical, and dynamical properties have been examined in this structural phase. The calculated electronic band structure and the total electronic density of states of our alloys indicated metallic behaviour. The estimated elastic constants show that these are stable and show anisotropic behaviour mechanically in β and γ phases. Also, the calculated phonon dispersion curves show that PdCoX (X = Si and Ge) alloys are stable dynamically in the same structural phases.

The structural, electronic, magnetic, and mechanical properties of perovskite oxides PbM1/2Nb1/2O3 (M = Fe, Co and Ni)

In this study, the structural, electronic, magnetic, and mechanical properties of perovskite oxides PbM1/2Nb1/2O3 (M = Fe, Co and Ni) are investigated. The systems are treated in ferromagnetic order. The calculations are carried out in the framework of density functional theory (DFT) within the plane-wave pseudopotential method. The exchange-correlation potential is approximated by generalized-gradient spin approach (GGA). The intra-atomic Coulomb repulsion is also taken into account in calculations (GGA + U). We have considered two generalized-gradient spin approximation functionals, which are Perdew–Burke–Ernzerhof (PBE) and PBE for solids (PBEsol) for structural parameter calculations when it included Hubbard potential. Although the spin-polarized electronic band structures of PbCo1/2Nb1/2O3 and PbNi1/2Nb1/2O3 systems exhibit metallic property in ferromagnetic phase, a bandgap is observed in spin-down states of PbFe1/2Nb1/2O3 resulting in half-metallic behavior. The main reason for this behavior is att...