Thermodynamic Properties and Phase Transition of Negative Thermal Expansion Materials

Abstract

Phonon properties and structural phase transition of negative thermal expansion material, ZrW₂O₈, were investigated from a thermodynamic point of view. Calorimetric investigation revealed that the phase transition involved the correlated orientational disordering of WO₄ units. In the ZrW₂O₈,-based solid solutions, the substitution effects on the phase transition were classified into two types. Spectrum analysis of heat capacity provided the phonon density of states of ZrW₂O₈, and HfW₂O₈, showing characteristic features of negative thermal expansion materials.