?? ????? ??????? ??? ????????????? ?????? ??????? ???? ??????? ????????????? ??? ???????? ?? 1978 ??? ?? ????? ?????? ???? ??? ?? 1980. ??????, ??????????? ??? 2020, ??????? 17 ???? ??? ??? ??????? 25 ?????????. ?? 1995 ?? ????? ??????????? ??? ????????? ?????? ???? ??????? ??? ??????, ???? ????????????????? ??? ???????? ??? ?????? ??? ????????? ?????? 8 ??? ??????????? ??? ??? ???? ??? ?????????. ?? ???????? ??? ????? ?????? ??? ????? ????????? ?? ????? ??????? ???? ?? ?? ????? ????????? ??????????? [1] ??? ?? ?????? ??????????? ???? ???????? [2], ???????? ??? Univ. of Southern California (???).

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서울 소재 7개 종합병원 암환자들의 보완대체요법 이용양상

Facile synthesis and characterization of conducting polymer-metal oxide based core-shell PANI-Pr2O–NiO–Co3O4 nanocomposite: As electrode material for supercapacitor

Advances and Perspectives for the Application of Perovskite Oxides in Supercapacitors

Synergistic effect of barium titanate nanoparticles and graphene quantum dots on the dielectric properties and conductivity of poly(vinylidenefluoride-co-hexafluoroethylene) films

PVDF-HFP/BaTiO3/GQDs polymer nanocomposite films with good flexibility and high dielectric constant (ϵ) at low frequency were prepared via solution casting technique. Different compositions of BaTiO3 (non-conducting ceramic nanofiller) and Graphene quantum dots (GQDs) (conducting nanofiller) utilized as co-filler were embedded in poly (vinylidene fluoride-co-hexafluoroethylene) (PVDF-HFP) polymer matrix. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning electron microscopy (SEM) techniques were employed to characterize the prepared nanocomposite films. The mechanical properties of PVDF-HFP/BaTiO3/GQDs nanocomposite films were also investigated. Dielectric properties of nanocomposite films such as dielectric constant (ϵ), dielectric loss (tanδ) and AC conductivity ( σac ) were also determined as a function of frequency and temperature. Highest ϵ with relatively low tanδ obtained at low frequency for maximum temperature in all polymer nanocomposite films. The σac increases from lower (100 Hz) to higher frequency up to 100 kHz and drops to zero for the further increment of frequency. These results suggest that the PVDF-HFP/BaTiO3/GQDs nanocomposites are the most promising materials for energy storage applications. 

Existence of nearest-neighbor and variable range hopping in Pr2ZnMnO6 oxygen-intercalated pseudocapacitor electrode

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.

Insulator to semiconductor transition in graphene quantum dots

Investigation of doping effect on electrical conduction mechanism and Li+ ion insertion/extraction in ZnO-XV2O5 {X=5% and 10%} electrode for superior energy storage application

A combined study of X-ray diffraction (XRD) pattern and Raman spectrum
authenticates the lower symmetric orthorhombic Pnma structure for solid-state
synthesized Pr2MgTiO6 (PMT). The Ag mode demonstrates itself as a breathing
vibration of the TiO6 octahedra. The ac conductivity, dielectric relaxation,
and impedance spectra highlight the joint contributions of the grain-boundaries
and grain microstructures to the charge carrier dynamics in PMT. The double
power-law formalism is accepted to fit ac conductivity spectra. The relaxation
spectra has a non-ideal nature with the circulation of relaxation time as
observed from the impedance spectroscopic data. An equivalent circuit model has
been employed for fitting impedance data using a constant phase element (CPE)
model. The dc conductivity investigation points towards a crossover from small
polaron hopping to Mott s variable range hopping due to lowering activation
energy. The crossover between two different conduction mechanisms (Mott s
variable range and small polaron hopping) is investigated using a conjunction
of thermal varying conductivity, dielectric relaxation and impedance spectrum
in polycrystalline PMT.

Crossover between small polaron hopping and Mott's variable range hopping in Pr2MgTiO6

Titanium based-perovskites have got surprising attraction due to their environment-friendly 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.

H. S. Tripathi

Papers

Existence of nearest-neighbor and variable range hopping in Pr2ZnMnO6 oxygen-intercalated pseudocapacitor electrode

Insulator to semiconductor transition in graphene quantum dots

Investigation of doping effect on electrical conduction mechanism and Li+ ion insertion/extraction in ZnO-XV2O5 {X=5% and 10%} electrode for superior energy storage application

Crossover between small polaron hopping and Mott's variable range hopping in Pr2MgTiO6

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