T − p phase diagrams and barocaloric effect in materials with successive phase transitions

Abstract

Abstract An analysis of the extensive and intensive barocaloric effect (BCE) at the successive structural phase transitions in some complex fluorides and oxyfluorides was performed. A high sensitivity of these compounds to a change of the chemical pressure allows one to vary successions and parameters of the transformations (temperature, entropy, baric coefficient) in wide ranges and obtain the optimal values of BCE. A comparison of different types of the schematic T − p phase diagrams with the complicated T(p) dependences observed experimentally shows that in some ranges of temperature and pressure BCE in compounds undergoing successive transformations can be increased due to summation of caloric effects associated with the distinct phase transitions. The maximum values of the extensive and intensive BCE in complex fluorides and oxyfluorides can be realized at rather low pressure, 0.1 – 0.3 GPa. In narrow temperature range around triple points the conversion from the conventional BCE to the inverse one is observed which is followed by gigantic change of both |∆SBCE| and |∆TAD|.