In this paper, various thermodynamic approaches to the structural phase transitions and the phonon properties
of the materials showing negative thermal expansion (NTE) in the wide temperature range are briefly reviewed through
three families of the NTE compounds; ZrW2O8, ZrV2O7, A2B3O12 (A = trivalent cation, B = W or Mo) families. As for the
structural phase transitions, the thermodynamic approaches provide us with elucidation of their mechanism from an entropic
point of view. The NTE is closely related to phonon properties. Heat capacity measured by calorimetry enables us
to estimate not only a Grüneisen function but also a distribution of phonon density of states, leading to specifying the
phonon modes with negative mode-Grüneisen parameters. It is demonstrated that the thermodynamic approach is powerful
to research the properties of the NTE materials.
Keywords: Entropy of transition, framework structure, Grüneisen function, heat capacity, mode-Grüneisen parameter, negative
thermal expansion, order-disorder phase transition, phonon, structural phase transition, thermal expansion, ZrW2O8.
Rights & PermissionsPrintExport