Heat capacity, thermal expansion and barocaloric effect in fluoride K2TaF7

Abstract

The heat capacity and thermal expansion of potassium heptafluorotantalate were studied. The room temperature phase P21=c is stable at least to 4 K. The strong first-order phase transition P21=c Pnma at T0 ¼ 486:2K is accompanied by giant changes in the entropy, DS0 ¼ 22:3 J ðmolKÞ 1; and volume strain, dV0=V ¼ 3:6%. A rather high sensitivity of K2TaF7 to pressure was found, dT0=dp ¼ 220KGPa 1. Significant extensive and intensive barocaloric effects are found at low pressure. The possibility of improving the barocaloric properties is discussed.