Showing papers by "Pushan Ayyub published in 1997"

Finite-size effects in antiferroelectric nanoparticles

Abstract: We study the size dependence of the antiferroelectric-to-paraelectric phase transition in ultrafine particles of (with x-ray domain size down to ) prepared by the sol - gel method. The phase transition was investigated by means of dielectric and thermal measurements. The nature of the particle size dependence of various properties of antiferroelectric was found to be generally similar to that of typical `displacive' ferroelectrics such as and . In both cases, a size-induced structural distortion towards the high-symmetry paraelectric phase appears to dictate the behaviour of the nanoparticulate system. Nanoparticles of `order - disorder' systems such as behave in a markedly different manner. With decreasing particle size, we observe an increasing deviation of the dielectric response from the Curie - Weiss behaviour. Certain physical situations that may lead to the observed smearing out of the transition in nanoparticles of and are discussed.

Vibrational Spectroscopic Study of the Semiorganic Nonlinear Optical Crystal Bis(thiourea)cadmium Chloride

Abstract: Polarized Raman and infrared spectra of bis(thiourea)cadmium chloride, a novel semiorganic nonlinear optical crystal, were recorded to determine the symmetries of molecular vibrations. The observed Raman and infrared bands are assigned to molecular vibrations of thiourea, cadmium–sulphur and cadmium–chloride bonds. The vibrational spectra are interpreted in the light of crystal structure data.