Spectroscopic investigations of phase transitions in complex solids

Spectroscopic methods have provided information of seminal importance in understanding phase transitions in solids. After briefly examining some fundamental concepts related to phase transitions, we shall discuss several case studies particularly involving the use of vibrational (IR and Raman) spectroscopy. Examples will include both order-disorder and displacive transitions. Under the former are included transitions in nitrates, ammonium halides, alkylammonium salts, plastic state of C₆₀ and superionic conductors (specially CsHSO₄). In addition, we shall discuss some aspects of incommensurate phase transitions, the glass transition and electronic phase transitions. Transitions of phosphonitrilic halide tetramers and alkane dicarboxylic acids are also examined.