Crystal phase stability and barocaloric efficiency of (NH4)3WO2F5

Calorimetric, dilatometric and pressure studies of (NH4)3WO2F5 were performed over a wide temperature range, including the Pm-3m <-> Pa-3 phase transition. Comparison of the obtained results with data for related fluorides (NH4)3SnF7 and (NH4)3TiF7 undergoing the same structural changes showed a significant role of chemical pressure in the formation of thermal and barocaloric properties. A decrease in anomalous entropy in oxyfluoride, S0 = 12.2 J/mol center dot K, is accompanied by a significant increase in sensitivity to hydrostatic pressure, dT0/dp = 93 K/GPa, the preservation of a large change in anomalous deformation delta( V/V)0 = 0.45% and a small temperature hysteresis, delta T0 < 1 K. This combination of thermal characteristics has led to both a significant increase in extensive and intensive barocaloric parameters in the low pressures area, and to their high reversibility in the modes of increasing and decreasing pressure.