Inelastic light scattering investigations on novel materials

Abstract

This thesis is unified more by the ubiquity and versatility of the use of inelastic light scattering (ILS) spectroscopy coupled with the two thermodynamic variables (pressure and temperature) within the realm of condensed matter physics than by the investigation of a single topic. The experimental investigations described in the resulting chapters each addresses discrete topics about different class of materials. Along with ILS, in order to understand specific material properties and open issues in these materials, the two thermodynamic variables, namely pressure and temperature were used wherever necessary. The thesis consists of six chapters and is divided into two parts (Part A and B). Introduction to general aspect of inelastic light scattering along with pressure and temperature effects on it, experimental details of Raman, Brillouin scattering and high pressure technique, high pressure Raman investigations on ZnBeSe ternary alloys, and high temperature Raman studies on Na2Cd(SO4)2 (NCSO) each occupies a chapter in Part A. Low temperature studies on acoustic phonons in pyrochlores RE2Ti2O7 (RE = Sm, Dy, Ho, Lu) and elastic properties of double walled carbon nanotubes (DWCNT), studied by Brillouin scattering each occupies a chapter in Part B. Each chapter includes a topical introduction about the material under investigation. Chapter 1 accounts a thorough introduction about the general aspects of inelastic light scattering (ILS). Effect of temperature and pressure on materials and how temperature or/and pressure studies integrated with ILS can be used to obtain useful information about material properties are also touched upon. ix Chapter 2 describes about the experimental details of the design and working principles of Raman and Brillouin scattering setup. The methods of doing high pressure Raman experiments have also been discussed. Chapter 3 contains high pressure Raman investigations up to about 25GPa on Zn1−xBexSe, an II-VI wide band gap ternary alloy. In this chapter, from the high pressure Raman studies, we discuss about nature of the alloy formation within the percolation picture, semiconductor-metal phase transition related to the structural stability of the alloy for different Be concentration of x= 11.6, 16 and 24% . Chapter 4 is about high temperature phase transition studies on a novel fast ion conductor material NCSO using Raman spectroscopy. This material shows two conductivity transitions at high temperature. In this chapter, role of SO4 ions in these conductivity transitions of NCSO is elucidated using Raman spectroscopy. Chapter 5 discusses low temperature acoustic phonon behavior studies in pyrochlores RE2Ti2O7 (RE = Sm, Dy, Ho, Lu) using Brillouin scattering. Here we have investigated subtle structural transitions in the pyrochlore lattice of Dy2Ti2O7 using temperature dependent Brillouin scattering from 300-25K. In Chapter 6, Brillouin scattering was used to investigate the acoustic properties of double walled carbon nanotubes (DWCNT). Here we have studied the bulk acoustic modes in DWCNT bundles and determine the average bulk sound velocity.