arXiv subjects

T. P. Sinha

Publications and source records attributed to T. P. Sinha.

16 recordsLinked to original sources

arXiv2026

Scaling of the Electrical Conductivity Spectra Reveals Distinct Transport Responses in A2SmTaO6 [A = Ba, Sr, Ca]

Disorder plays an important role in materials science, influencing material behavior across different length scales. Imperfections like vacancies, atomic substitutions, lattice distortions, and microstructural inhomogeneities, disrupt ideal periodicity thereby altering physical properties. Analogous to spin-glass systems, electrical 'glassiness' arises when charge carriers confront disordered energy landscapes, leading to a broad range of relaxation times, especially in polycrystalline materials where dipoles experience competing exchange interactions. Complex impedance, permittivity, and electric modulus distill out separate resistive and capacitive effects, offering insights into how microstructural inhomogeneities affects conduction mechanism. In polycrystalline double perovskites A2SmTaO6 (A = Ba, Ca), with a power law driven ac conductivity, the hopping and relaxation of carriers is affected by both grains and grain boundaries. Scaling of ac conductivity and impedance response reveals correlation between conduction and relaxation timescales. The inhomogeneities in local energy landscape of 'frustrated' dipoles restrict the 'universality' of conduction mechanism across the bulk length scale.

cond-mat.mtrl-sci↗

arXiv2023

Triclinic BiFeO3: A room-temperature multiferroic phase with enhanced magnetism and resistivity

The magnetic and transport properties of BiFeO3/La2NiMnO6 (BFO/LNMO) composite have been investigated both experimentally and theoretically. Unlike the normal rhombohedral (R3c) phase, BFO in the composites is crystallized in the triclinic phase (P1). Interestingly, the composites demonstrate a significant enhancement in the magnetization, magnetoelectric coupling and show higher resistivity than that of the regular BFO (R3c). As LNMO has its Curie temperature at 280 K, the room temperature and above room temperature magnetic contribution in the composites is expected to be from the triclinic BFO phase. Experimentally observed enhancement in magnetization is validated using classical Monte Carlo simulation and density functional theory (DFT) calculations. The calculations reveal higher magnetic moments in triclinic BFO as compared to the rhombohedral BFO. Overall, this study reveals triclinic BFO as the promising room temperature multiferroic phase which is helpful to optimize the multiferroicity of BFO and achieve wider applications in future.

cond-mat.mtrl-sci↗

arXiv2023

Phase transition in oxygen-intercalated pseudocapacitor Pr$_2$MgZrO$_6$ electrode: A combined structural and conductivity analysis

The phase transition behavior and charge storage mechanism of Pr$_2$MgZrO$_6$ (PMM), an oxygen-intercalated pseudocapacitor, were investigated through crystal structure analysis, Raman spectroscopy, ac conductivity spectroscopy, X ray photoelectron spectroscopy, and electrochemical spectroscopy. The crystal structure analysis and vibration studies revealed a phase transition in PMM, following the sequence 14 to 87 to 225. High temperature Raman spectroscopy demonstrated a significant feature of a monoclinic to tetragonal phase transformation in PMM. The ac conductivity spectroscopy exhibited a semiconductor to metal transition in PMM. X-ray photoelectron spectroscopy of the Mn 2p state confirmed the presence of oxygen vacancies in PMM at room temperature. Furthermore, the electrochemical performance of PMM as an electrode was evaluated. The PMM electrode displayed an intercalated pseudocapacitive nature, exhibiting a maximum possible specific capacitance of 257.57 F. The charge storage process of the PMM electrode was thoroughly reviewed and discussed, shedding light on the underlying mechanisms.

cond-mat.mtrl-sci↗

arXiv2023

Exploring the Electrical Transport Properties and Insulator-Metal Transition in Polycrystalline Pr$_2$MgZrO$_6$: Insights from Conductivity and Impedance Spectroscopy

The ac electrical transport properties of polycrystalline Pr$_2$MgZrO$_6$ (PMZ) have been investigated using conductivity and impedance spectroscopic techniques. The crystal structure of PMZ has been determined to be monoclinic through a combination of X-ray diffraction and Raman spectroscopic studies. Ag mode in the Raman spectra has been identified as the breathing vibration of the ZrO6 octahedra. The ac conductivity spectra of PMZ exhibit distinct characteristics at different temperature ranges. At lower temperatures (less than 420 K), the spectra are fitted using a double power law, indicating the involvement of multiple microstructural features. On the other hand, at higher temperatures (greater than 460 K), the spectra follow Jonscher's law, suggesting a simpler conduction mechanism. Through the analysis of conductivity, permittivity, and impedance, an insulator-metal transition has been observed around 452 K. This transition signifies a significant change in the electrical properties of PMZ and provides valuable insights into its conductive nature.

cond-mat.mtrl-sci↗

arXiv2023

Existence of nearest-neighbor and variable range hopping in Pr$_2$ZnMnO$_6$ oxygen-intercalated pseudocapacitor electrode

X-ray diffraction pattern and Raman spectrum authenticate the monoclinic P21/n structure of polycrystalline Pr$_2$ZnMnO$_6$ (PZM) synthesized by the solid-state reaction technique. The X-ray photoemission spectrum suggests the existence of oxygen vacancy in PZM, which plays a crucial role in electrical conduction as well as in electrochemical behavior. The existence of two different conduction mechanisms (such as nearest-neighbor hopping (NNH) and Mott variable range hopping (MVRH)) is observed from the investigation of dc conductivity studies, dielectric relaxation, and impedance analysis of PZM. It is found that below 580 K, there is a transition from NNH to MVRH due to the decrease of activation energy. The constant phase element model is used to correlate the Nyquist plot and electric modulus of PZM. The bulk PZM electrode exhibits intercalated pseudocapacitive nature which offers an efficient specific capacitance of 69.14 F/g at a charge and discharge currents of 2 A/g in an aqueous solution of 1 M KOH. The charge storage mechanism of the PZM electrode has been analyzed and discussed.

cond-mat.mtrl-sci↗

arXiv2023

Hopping mechanisms, photoluminescence studies toward highly efficient UV-responsive Pr2MgTiO6 photocatalyst

Titanium based-perovskites have got surprising attraction due to their environmentfriendly photocatalysts behavior. The Rietveld refinement of X-ray diffraction (XRD) pattern authenticates the orthorhombic Pnma structure of Pr2MgTiO6 (PMT). The Pr3+-Ti4+ intervalence charge transfer process plays an important role inside PMT. The dc conductivity shows a change in the hopping mechanism from nearest-neighbor hopping to a variable range hopping due to the activation energy reduction. This change in the hopping mechanism is well supported by both the relaxation time and impedance data in PMT. The constant phase element (CPE) model is utilized to fit impedance plots. The photocatalytic activity of PMT was performed under UV irradiation with the help of degradation kinetics of organic pollutants. Also, the photocatalytic efficiency of recycled and reused PMT finds 91.2% after 5th cyclic runs. The calculated band-gap is found to be 3.58 eV.

cond-mat.mtrl-sci↗

arXiv2022

Tailoring the magnetic landscape in Al-doped LaMnO3: An experimental and computational perspective

We have presented the synthesis, structural, and magnetic properties from the experimental point of view. Then we verified our experimental observation by studying the electronic and magnetic properties of Al-doped LaMnO3 from the first principle density functional theory (DFT) and Monte-Carlo simulation. We have synthesized the LaAlxMn1-xO3 (x= 0.05, 0.15, 0.25) and performed the Rietveld refinement of XRD data to determine the lattice parameters. To see the mixed valance of Mn-ion, we performed the XPS of 25% Al-doped material. The magnetic study shows the ferromagnetic transition of these materials. Using XRD refinement values, we have completed the DFT calculations. The Monte Carlo simulation has been done through the anisotropic Ising model to analyze the origin of magnetic transition. We have determined the anisotropy and the interaction constants from the DFT calculations.

cond-mat.mtrl-sci↗

arXiv2021

Dynamic Spin Fluctuations in the Frustrated Spin Chain Compound Li$_3$Cu$_2$SbO$_6$

We report the signatures of dynamic spin fluctuations in the layered honeycomb Li$_3$Cu$_2$SbO$_6$ compound, with a 3$d$ S = 1/2 $d^9$ Cu$^{2+}$ configuration, through muon spin rotation and relaxation ($μ$SR) and neutron scattering studies. Our zero-field (ZF) and longitudinal-field (LF)-$μ$SR results demonstrate the slowing down of the Cu$^{2+}$ spin fluctuations below 4.0 K. The saturation of the ZF relaxation rate at low temperature, together with its weak dependence on the longitudinal field between 0 and 3.2 kG, indicates the presence of dynamic spin fluctuations persisting even at 80 mK without static order. Neutron scattering study reveals the gaped magnetic excitations with three modes at 7.7, 13.5 and 33 meV. Our DFT calculations reveal that the next nearest neighbors (NNN) AFM exchange ($J_{AFM}$ = 31 meV) is stronger than the NN FM exchange ($J_{FM}$ = -21 meV) indicating the importance of the orbital degrees of freedom. Our results suggest that the physics of Li$_3$Cu$_2$SbO$_6$ can be explained by an alternating AFM chain rather than the honeycomb lattice.

cond-mat.str-el↗

arXiv2019

Temperature dependent conductivity mechanisms observed in Pr2NiTiO6

The crossover between two different conduction mechanisms (variable range and small polaron hoppings) is probed utilizing a conjunction of thermally varying conductivity and impedance in polycrystalline Pr2NiTiO6 (PNT). A combination of X-ray diffraction (XRD) and Raman spectroscopic investigations authenticates the lower symmetric monoclinic structure for PNT. The conductivity, impedance and relaxation spectra highlight the combined contributions of the electrodes, grain-boundaries and grain microstructures to the carrier dynamics in PNT. The relaxation mechanism has a non-ideal nature with distribution of relaxation times as observed from the dielectric and impedance spectroscopic data. The dc resistivity investigation points towards a transition in the conduction mechanism showing a gradual crossover at temperature 490 K, from small polaron hopping to Mott s variable range hopping due to reduced activation energy.

cond-mat.mtrl-sci↗

arXiv2019

The X-ray photoemission and Co K -Edge X-ray absorption of Ba2CoWO6

The structural, electronic and optical properties of cubic double perovskite BaCoWO6 have been studied. Neutron powder diffraction data is collected on this sample from 6K to 300K. The crystal structure is face centered cubic, space group being Fm3m (No. 225). We did not find evidence for long range magnetic ordering in this system in this temperature range. The band-gap is estimated using Uv-vis spectroscopy. The Co-K edge X-ray absorption (XAFS) spectra of Ba2CoWO6 was analysed together with those Co-foil, which was used as reference compounds. X-ray photoemission spectroscopy (XPS), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies give the insight of the electronic and structural information on the Co local environment for Ba2CoWO6.

cond-mat.mtrl-sci↗

arXiv2019

Insulator to Semiconductor Transition in Graphene Quantum Dots

Zero dimensional graphene quantum dots (GQDs) exhibit interesting physical and chemical properties due to the edge effect and quantum confinement. As the number of carbon atoms in edge is more than on basal plane, GQDs are more reactive. Room temperature XRD pattern confirms the formation of the GQDs. UV-Visible spectra confirm that GQDs show optical absorption in the visible region. The emission peaks in the photoluminescence spectra are red shifted with the increase of excitation wavelength. Dynamic light scattering (DLS) analysis shows that the average size of the particles is found to be 65 nm. The frequency dependent electrical transport properties of the GQDs are investigated in a temperature range from 300 to 500 K. Most interestingly, for the first time, the insulator to semiconductor transition of GQD is observed near 400K. The transition mechanism of GQD is discussed with detailed dielectric analysis. The effects of intercalated water on temperature dependent conductivity are clearly discussed. The dielectric relaxation mechanism is explained in the framework of permittivity, conductivity and impedance formalisms. The frequency dependent ac conductivity spectra follows the Jonscher s universal power law. Cole-Cole model is used to investigate the dielectric relaxation mechanism in the sample.

cond-mat.mtrl-sci↗

arXiv2018

Synthesis, structural and photo physical properties of perovskite oxide (KNbO3)1-X+(La2NiMnO6)X for photovoltaic application

Solid solutions of perovskite oxides (KNbO3)1-x+(La2NiMnO6)x (x=0, 0.1, 0.2 and 0.3) with a variation of band gap (1.33-3.6 eV) have been introduced as a promising photovoltaic absorber. The structural characterization of the prepared samples was carried out using X-ray diffraction (followed by Rietveld refinement) and Raman experiment. As the doping percentage of the monoclinic La2NiMnO6 in the solid-solution increases, the crystal structure of host KNbO3 becomes more symmetric from orthorhombic to cubic. A large reduction in the particle size has also been observed in the solid solutions in comparison to the pure KNbO3. The band gap (~ 1.33 eV) of the synthesized solid solution x=0.1 is found to be very close to the Shockley-Queisser band gap value of 1.34 eV, which suggests the promising photovoltaic possibility in this material. Photoluminescence (PL) emission spectra reveal a strong PL quenching in the solid-solutions in comparison to the KNbO3. The overall structural and optical studies suggest the promising photovoltaic possibility in KNbO3/ La2NiMnO6 solid solution.

cond-mat.mtrl-sci↗

arXiv2017

Structural and dielectric characterization of Sm2MgMnO6

The polycrystalline Sm2MgMnO6 (SMMO) was synthesized at 1173K by means of sol-gel technique. Rietveld refine-ment of X-ray diffraction (XRD) pattern confirmed the formation of a single phase monoclinic structure with space group P21/n. The band gap achieved from UV-vis spectra shows the semiconducting nature of the material. To observe the effect of grains and grain-boundaries in the conduction process and dielectric relaxation measurements are carried out on SMMO sample at different frequencies between 313 K and 673 K. An electrical equivalent circuit consisting of the resistance and constant phase element is used to clarify the impedance data.

cond-mat.mtrl-sci↗

arXiv2015

Optical and Electronic Properties of Double Perovskite Ba2ScSbO6

Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Riedvelt analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy to be 4.2eV. A detailed study of the electronic properties has also been carried out using the Full-Potential Linear Augmented Plane Wave (FPLAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications, such as dielectric resonators and filers in microwave applications

cond-mat.mtrl-sci↗

arXiv2014

Half metallic ferromagnetism in tri-layered perovskites Sr$_4$T$_{3}$O$_{10}$ (T=Co, Rh)

First-principles density functional theory (DFT) is used to investigate the electronic and magnetic properties of Sr$_4$Rh$_3$O$_{10}$, a member of the Ruddlesden-Popper series. Based on the DFT calculations taking into account the co-operative effect of Coulomb interaction ($U$) and spin-orbit couplings (SOC), Sr$_4$Rh$_3$O$_{10}$ is found to be a half metallic ferromagnet (HMF) with total angular moment $μ_{\rm {tot}}$=12$μ_B$ per unit cell. The material has almost 100$\%$ spin-polarization at the Fermi level despite of sizable SOC. Replacement of Rh atom by the isovalent Co atom is considered. Upon full-replacement of Co, a low-spin to intermediate spin transition happens resulting in a HMF state with the total angular moment three-time larger (i.e. $μ_{\rm {tot}}$=36$μ_B$ per unit cell), compared to Sr$_4$Rh$_3$O$_{10}$. We propose Sr$_4$Rh$_3$O$_{10}$ and Sr$_4$Co$_3$O$_{10}$ as candidates of half metals.

cond-mat.mtrl-sci↗

arXiv2002

Optical properties of perovskite alkaline earth titanates : a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline earth titanates CaTiO_3, SrTiO_3 and BaTiO_3 and compare our results with available data on optical properties of these systems.

cond-mat.mtrl-sci↗