arXiv subjects

Vinod Singh

Publications and source records attributed to Vinod Singh.

4 recordsLinked to original sources

arXiv2026

Physical and Dielectric Properties of Polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$

We report a detailed investigation of the structural, electronic, vibrational, and dielectric properties of polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$ samples, prepared at two sintering temperatures (1000\degree C and 1250\degree C). The introduction of Nb$^{5+}$ at the V$^{5+}$ site leads to notable structural and vibrational changes, which can be attributed to their isoelectronic nature and the comparatively larger ionic radius of Nb$^{5+}$. The Rietveld refinement of the X-ray diffraction patterns confirms a coexistence of monoclinic ($P$2$_{1}$/$n$) and scheelite-type tetragonal ($I$4$_{1}$/$a$) phases; for example, with a fraction of 4\% and 96\% for the sample annealed at 1250\degree C. The particle morphology has altered from spherical (1000\degree C) to irregular-shaped (1250\degree C) as a result of increase in annealing temperature. The Raman spectroscopy, Fourier Transform Infrared spectroscopy and X-ray Photoemission Spectroscopy have been used to understand the vibrational and electronic properties. An optical band gap of 2.7~eV for the sample sintered at 1250\degree C is calculated using Ultraviolet-vis diffuse reflectance spectroscopy measurements. The dielectric studies shows the higher dielectric permittivity ($\epsilon$$_{r}$) and lower dielectric loss for the sample annealed at 1250\degree C.

cond-mat.mtrl-sci↗

arXiv2023

Dielectric behavior and impedance spectroscopy of Niobium substituted Lanthanum based orthovanadates at high temperatures

We present the detailed study of the temperature dependent dielectric properties, impedance spectroscopy and electrical conductivity of LaV$_{1-x}$Nb$_x$O$_4$ ($x=$ 0-1) samples prepared by the solid-state reaction method. The dielectric constant ($ε_r'$) increases (decreases) with increase in the temperature (frequency); while, the magnitude of $ε_r'$ remains almost invariant (order of 10$^4$ at 100~Hz and 600\degree C) with $x$. The single phase $x=$ 0 (monoclinic-monazite, $P2_1/n$) and $x =$ 1 (monoclinic fergusonite, $I2/a$) samples show the lower values of loss factor [tan$δ=$ (4-8)] as compared to the $x=$ 0-0.8 samples [tan$δ=$(12-18)] having mixed tetragonal and monoclinic phases, which indicates the strong correlation between the crystal structure and the dielectric properties. The real part of impedance decreases with both temperature and frequency, and the observed weak relaxation remains almost unaltered with $x$. The imaginary part of impedance shows strong relaxation peaks shifting towards higher temperatures with frequency, which is attributed to the effect of grains, grain boundaries, and electrodes in the samples. The activation energy of the relaxation process is estimated to be 0.8-1.0~eV for the $x=$ 0-0.6 samples, and $\approx$1.4~eV for the $x=$ 0.8; whereas the $x=$ 1 sample shows two values ($\approx$0.5~eV and $\approx$1.0~eV) in the higher and lower temperature range, respectively. Further, the change in total conductivity with the angular frequency, which found to be in the range of 10$^{-3}$ to 10$^{-5}$~S/m, is fitted using the Jonsher power law. The analysis suggests the OLPT model for all the samples, whereas the $x$ = 1 sample exhibit a transition near 480\degree C and at higher temperatures it shows NSPT and QMT. This transition is corroborated by the tangent loss curves and may be associated with the change in structure.

cond-mat.mtrl-sci↗

arXiv2023

Structural, vibrational and electronic properties of Nb substituted orthovanadates LaV$_{1-x}$Nb$_x$O$_4$

We investigate the structural, vibrational, morphological, and electronic properties of Nb substituted orthovanadate LaV$_{1-x}$Nb$_x$O$_4$ samples prepared by the solid-state reaction method. The x-ray diffraction (XRD) analysis reveals the presence of three crystal structures [monoclinic monazite ($m-m$) type for the $x=$ 0, two-phase equilibrium of monoclinic monazite ($m-m$) and tetragonal scheelite ($t-s$) type for the 0.2$\leq$$x$$\leq$0.8, and monoclinic fergusonite ($m-f$) type for the $x=$ 1 samples] with an increase in Nb$^{5+}$ concentration. The Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were employed to study the vibrational and electronic properties of all the samples, respectively. In order to choose an excitation wavelength that does not cause undesirable fluorescence and has observable intensities of all the vibrational modes, the Raman spectra are collected using 532 nm, 633 nm, and 785 nm laser lines. With increasing the Nb$^{5+}$ concentration, new Raman modes associated with Nb-bonds are clearly visible and the intensity of V-bonds assigned modes is decreasing. The XPS analysis shows the unchanged 3+ oxidation state of La ion where the intensity of the V 2$p$ core-level decreases while the Nb 3$d$ core-level increases with $x$. The equal spin-orbit energy splitting of the states is confirmed by the average energy difference (across La core-level spectra for all the samples) for state I as well as bonding and anti-bonding of state II. Interesting, the relative intensity of La 3$d$ state I and state II show systematic change with Nb doping altering the metal ligand overlap. We discuss and provide insight into the evolution of the structural, morphological, and chemical features with Nb substitution in LaV$_{1-x}$Nb$_x$O$_4$ samples.

cond-mat.mtrl-sci↗

arXiv2014

Topological Dyons

Using a two potential approach, dyon solutions have been found in the temporal and non-temporal gauges for a non-Abelian theory. Both the charges, electric and magnetic, of the temporal dyon solution are topological, while for the non-temporal case both charges are partially topological.

hep-th↗