Calorimetric and Dilatometric Studies on Successive Phase Transitions in Ferroelastic NH₄BeF₃

Abstract

The specific heat and thermal expansion of NH₄BeF₃ were measured. The crystal undergoes successive phase transitions at −22°C, 60°C and 253°C. The transition entropies were deduced from the data of the specific heat to be 0.66 cal/mol·deg for the phase transition at −22°C and 0.40 cal/mol·deg for the ferroelastic phase transition at 60°C, respectively.