arXiv subjects

Moumin Rudra

Publications and source records attributed to Moumin Rudra.

7 recordsLinked to original sources

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↗

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

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↗

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↗