Heat capacity, thermal expansion and barocaloric effect in fluoride K2TaF7

Flerov, I. N.; Gorev, M. V.; Kartashev, A. V.; Pogorel'tsev, E. I.; Laptash, N. M. Source: JOURNAL OF MATERIALS SCIENCE, 54 (23):14287-14295; 10.1007/s10853-019-03924-8 DEC 2019

The heat capacity and thermal expansion of potassium heptafluorotantalate were studied. The room temperature phase $P 2_{1} / c$ is stable at least to 4 K. The strong first-order phase transition $P 2_{1} / c - P n m a$ at $T_{0} = 486.2 K$ is accompanied by giant changes in the entropy, $Δ S_{0} = 22.3 J (mol K)^{- 1},$ and volume strain, $δ V_{0} / V = - 3.6 %$ . A rather high sensitivity of $K_{2} {TaF}_{7}$ to pressure was found, $d T_{0} / d p = - 220 K G {Pa}^{- 1}$ . Significant extensive and intensive barocaloric effects are found at low pressure. The possibility of improving the barocaloric properties is discussed.