• V G Kher

      Articles written in Pramana – Journal of Physics

    • X-ray study of some spinels containing gallium and manganese

      P D Bhalerao D K Kulkarni V G Kher

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      The ternary oxides CrMnGaO4, NiMnGaO4, CuMnGaO4 and ZnMnGaO4, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga3+ [Mn2+ Cr3+] O42−. Ga3+ [Cu2+ Mn3+] O42−, Mn2+ [Ga3+ Ni3+] O42− and Zn2+ [Mn3+ Ga3+] O42−.

    • Electric polarization and dielectric behaviour in dc electric fields of fused KNO2 in phase II at room temperature

      V G Kher V N Hete D A Deshpande

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      On application of dc electric fields to a sample of KNO2 (99.9% pure) fused between two heavily nickel plated copper plates the sample does not acquire the potential difference equal to the applied emf even though there is no external potential drop in the circuit. Also a very large capacitance of the order of 3000µF is obtained for this sample which is attributed to interfacial polarization effect. An equivalent circuit is given to explain the dc electrical behaviour of the sample. The idea of solid state battery does not seem to be applicable in the case of fused KNO2. The large value of the capacitance for dc fields in series with large voltage-dependent resistance is the cause of the slow discharge of the condenser.

    • Electroluminescence in lead titanate single crystals

      D A Deshpande K R Bagree B A Patki V G Kher

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      Electroluminescence in PbTiO3 single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration suggest that there is a self maintained discharge in the dielectric due to secondaryγp mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγp andγi are active after the application of a high field and the critical field at which this occurs decreases with increase in the frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the dielectric due to an avalanche formation.

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