Anup Pradhan Sakhya

Electronic, optical and thermoelectric properties of PrMO3 (M = Al, Ga, In) from first-principles calculations

We have systematically investigated the electronic structure, optical properties, Born effective charges and the thermoelectric properties of PrMO3 (M = Al, Ga, In) compounds using first-principles density functional theory calculations. Two different density functional approaches, the full potential linearized augmented plane wave method (FP-LAPW) and the plane wave pseudo potential method were used for the present study. A direct band gap at a Γ point of 3.8 eV, 3.07 eV and 2.9 eV is observed for PrAlO3 (PAO), PrGaO3 (PGO) and PrInO3 (PIO). The optical anisotropy of PAO and PGO is revealed from the computed optical properties such as complex dielectric function, refractive index, and absorption coefficient whereas PIO is found to be optically isotropic in the low energy range making it suitable for use in the development of ceramic scintillators. The inter-band transitions to the optical properties are analyzed with the help of calculated band structures. The Born effective charge and the static dielectric tensor of these materials have also been calculated.

Dielectric relaxation and Ac conductivity of perovskites CH3NH3PbX3 (X = Br, I)

ABSTRACT MAPbX3 (MA = CH3NH3, X = Br, I) are synthesized by the chemical route. The Rietveld refinement of the room temperature X-ray diffraction pattern of the materials shows that MAPbBr3 is crystallized in the cubic Pm3m crystal symmetry whereas MAPbI3 crystallizes in the tetragonal phase with space group I4/mcm. The dielectric relaxation of MAPbX3 has been studied in the frequency range from 42 Hz to 0.2 MHz in the electric modulus formalism. The relaxation time is determined by the reciprocal of the frequency where the maximum of the imaginary part of the electric modulus is centred. The relaxation mechanism of the samples is investigated by the Cole-Cole model. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a capacitance. The frequency dependent conductivity spectra follow the power law.

Band-gap engineering of La1-xNdxAlO3（x = 0,0.25,0.50,0.75,1）perovskite using density functional theory：A modified Becke Johnson potential study

The structural, electronic, and magnetic properties of the Nd-doped Rare earth aluminate, La1−x Nd x AlO3 (x = 0% to 100%) alloys are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The effects of the Nd substitution in LaAlO3 are studied using the supercell calculations. The computed electronic structure with the modified Becke–Johnson (mBJ) potential based approximation indicates that the La1−x Nd x AlO3 alloys may possess half-metallic (HM) behaviors when doped with Nd of a finite density of states at the Fermi level (E F). The direct and indirect band gaps are studied each as a function of x which is the concentration of Nd-doped LaAlO3. The calculated magnetic moments in the La1−x Nd x AlO3 alloys are found to arise mainly from the Nd-4f state. A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at E F. The observed decrease of the band gap with the increase in the concentration of Nd doping in LaAlO3 is a suitable technique for harnessing useful spintronic and magnetic devices.

Origin of the optical anisotropy and the electronic structure of Ru-based double perovskite oxides: DFT and XPS studies

Experimental and theoretical studies of the electronic structure of Pr2LiRuO6 (PLR), Nd2LiRuO6 (NLR) and Sm2LiRuO6 (SLR) crystals are reported. The linear optical properties of these compounds have been investigated using density functional theory calculations. The optical anisotropy in these compounds is revealed from their computed optical properties, such as their complex dielectric functions and refractive indices. The calculations show that SLR has a relatively large birefringence (Δn = 0.06) compared to NLR and PLR, which is important for mid-infrared nonlinear optical applications. We propose that the O 2p to Ru 4d transition is primarily responsible for the origin of optical activity in these materials while the origin of the optical anisotropy in these materials results from the asymmetrically oriented Ru–O bonds in the RuO6 octahedra of the unit cell. The evolution of the Ru 3d core-level signals as obtained from the X-ray photoemission spectroscopy measurements provide confirmation of a dynamic increment in the electron correlations as we move from PLR and NLR to SLR.

Vibrational modes and electronic structure of Sr2GdTaO6

The electronic structure of Sr2GdTaO6 (SGT) synthesized by solid state reaction technique, has been investigated by first-principles calculations and the eigen frequencies of different phonon modes have been calculated. The calculated DOS indicates a band gap of 3.30 eV between the top most valence band of O-2p character and the bottom of conduction band of Ta-5d character. The interaction between O-p state and Ta-d state is responsible for conduction mechanism in SGT as observed in DOS spectrum. Fourier transform infrared (FTIR) spectrum shows two primary phonon modes of the sample at around 373 cm−1 and 562 cm−1. Raman spectrum of the sample taken at 488 nm excitation wavelength shows four primary strong peaks at 150, 420, 560 and 790 cm−1. Lorentzian lines with 18 bands have been used to fit the Raman spectrum.

Structural and transport properties of NdCrO[sub 3] nanoceramics

Reitveld refinement of the room temperature powder X-ray diffraction profile of NdCrO3 (NCO) nanoceramics synthesized by sol-gel processing shows orthorhombic Pnma (D2h16) space group symmetry. The refined lattice parameters are a = 5.482(3) A, b = 7.689(4) A and c = 5.416(3) A. Transmission electron microscopy (TEM) of NCO shows that the average particle size is around 70 nm. The electrical transport property of NCO is investigated by both conductivity and electric modulus formalism. The electrical data is taken by a LCR meter in a temperature range from 303 K to 573 K and in a frequency range from 42 Hz to 1.1 MHz. The ac conductivity follows a power law. The Cole-Cole plot of impedance at 303 K shows grain effect.