Structural Phase Transitions

Abstract

This article discusses the application of NMR spectroscopy to the study of structural phase transitions in solids. The various classifications of solid-solid phase transitions are presented. The changes in NMR lineshapes that accompany site symmetry changes during a phase transition are explained. The order-disorder and displacive phase transitions are described as well as how these two types of phase transitions can be distinguished by NMR spectroscopy. Changes in molecular and atomic dynamics frequently occur during structural phase changes. A description of how these changes affect NMR lineshapes and relaxation times is presented. A brief explanation of how Landau theory can be used to relate NMR spectroscopy and structural phase transitions is also presented. Keywords: phase transitions; NMR spectroscopy; Landau theory; displacive phase transition; order-disorder phase transition; soft modes; spin-lattice relaxation; quadrupolar coupling constant; chemical shift