RAMAN SCATTERING STUDIES OF LEAD ORTHOVANADATE

Abstract

This work is a report on experimental temperature dependent laser Raman scattering studies of lead orthovanadate. The Raman spectra of this crystal were recorded at both high (above room temperature) and low (below room temperature) temperatures. The spectra were obtained in the temperature range 77 to 405 K and also at 10 K. Thus this study covers the three known phases of the crystal. We begin in Chapter l with a description of lead orthovanadate, in particular its crystal structure, space group, unit cell parameters etc, and some of its notable physical properties, for example, ferroelectricity, and ferroelasticity in its different phases. A brief review of all past work, chiefly experimental, on this crystal that could be found is given next. We then discuss Raman scattering studies and the application of such studies to lead orthovanadate. Chapter 2 contains a discussion of the symmetry analysis of normal modes which allows us to enumerate and classify the vibrational modes of a crystal. Two different methods of symmetry analysis, nuclear site group analysis and molecular site group analysis, are applied to the three different phases of lead orthovanadate. The details of these analyses are given. In Chapter 3 the experimental procedure is presented together with a description of the experimental set-up. The crystal samples are described. Finally a discussion and estimate of errors are given. The experimental results are presented in Chapter 4. The Raman spectra in each of the three phases are described together with the changes that occur in the spectra during the phase transitions. Figures of the Raman spectra are also given. Chapter 5 contains a discussion of the results and their connection with other work reported in the literature. In particular, the vibrational modes of lead orthovanadate and the. changes associated with the phase transitions are discussed. The conclusion is presented in Chapter 6.