http://dyuthi.cusat.ac.in:80/xmlui/handle/purl/687 2013-05-25T01:21:44Z 2013-05-25T01:21:44Z Santhakumari, N C Vallabhan, C P G http://dyuthi.cusat.ac.in:80/xmlui/handle/purl/2659 2011-12-17T20:30:17Z 1992-05-01T00:00:00Z

Electrical conductivity, dielectric properties and phase transition in ethylenediammonium sulphate single crystals Santhakumari, N C; Vallabhan, C P G D.C. and a.c. electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium sulphate, (H3NCH2CH2NH3)(SO4), have been measured axiswise as a function of temperature. Anomalous variations in all the above properties at 480 K indicate the occurrence of a phase transition in the above material at this temperature. The existence of such a phase transition is also confirmed by DSC measurements. Electrical conductivity results are analysed and the activation energies of conduction at different temperature regions have been evaluated from the logσ vs 103T−1 plot. Possible mechanisms for the electrical conduction process are discussed, the available results being in favour of a proton transport model.

1992-05-01T00:00:00Z Sankara Raman, S Nampoori, V P N Vallabhan, C P G Saravanan, N Mohammed Yusuff, K K http://dyuthi.cusat.ac.in:80/xmlui/handle/purl/2658 2011-12-17T20:30:26Z 1996-01-01T00:00:00Z

Measurement of thermal diffusivity of some halogeno benzimidazole complexes of cobalt(II), copper (II) and copper(I) using laser induced photoacoustic effect Sankara Raman, S; Nampoori, V P N; Vallabhan, C P G; Saravanan, N; Mohammed Yusuff, K K

1996-01-01T00:00:00Z Vidyalal, V Rajasree, K Vallabhan, C P G http://dyuthi.cusat.ac.in:80/xmlui/handle/purl/2657 2011-12-17T20:30:26Z 1996-01-01T00:00:00Z

Measurements of Electromagnetic Shielding Effect Using Htsc Materials Vidyalal, V; Rajasree, K; Vallabhan, C P G A simple experimental set-up is described to measure the electromagnetic shielding property of high Tc superconducting samples. Measurements were performed using HTSC materials in the form of laser ablated thin films, powders and sintered pellets. Samples used were Gd-123 in pure and doped form as well as a few Bi-based superconducting ceramics. For comparison, similar measurements were carried out on metals like aluminium, copper and μ metal. Very effective shielding was observed for HTSC materials compared to the conventional materials mentioned above. However it also depended on the sample types and poor shielding was observed for powdered HTSC material in comparison to thin films prepared by laser ablation.

1996-01-01T00:00:00Z Jayaraj, M K Vallabhan, C P G http://dyuthi.cusat.ac.in:80/xmlui/handle/purl/2652 2011-12-17T20:30:22Z 1989-10-01T00:00:00Z

Dielectric and optical properties of europium oxide films Jayaraj, M K; Vallabhan, C P G The dielectric properties of vacuum-deposited europium oxide films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300-543 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 Å. Films deposited at higher substrate temperatures (above 423 K) exhibit improved dielectric properties owing to the recovery of stoichiometry. The frequency variation of the loss factor exhibits a minimum which increases with rise in temperature. The breakdown field strength (about 106V cm-1) is found to be thickness dependent and it varies in accordance with the Forlani-Minnaja relation. The films exhibit ohmic conduction with an activation energy of 0.86 eV at low electric fields but at higher fields the conductivity becomes space charge limited. X-ray studies show that the films are amorphous in nature. The a.c. conductivity is proportional to ω at low frequency, whereas a square law dependence is observed at higher frequencies. The optical constants n, α and k and optical band gap are calculated from the UV-visible-near-IR spectra.

1989-10-01T00:00:00Z