Giant adiabatic temperature change and its direct measurement of a barocaloric effect in a charge-transfer solid.

Solid refrigerants exhibiting a caloric effect upon applying external stimuli are receiving attention as one of the next-generation refrigeration technologies. Herein, we report a new inorganic refrigerant, rubidium cyano-bridged manganese-iron-cobalt ternary metal assembly (cyano-RbMnFeCo). Cyano-RbMnFeCo shows a reversible barocaloric effect with large reversible adiabatic temperature changes of 74 K (from 57 °C to -17 °C) at 340 MPa, and 85 K (from 88 °C to 3 °C) at 560 MPa. Such large reversible adiabatic temperature changes have yet to be reported among caloric effects in solid-solid phase transition refrigerants. The reversible refrigerant capacity is 26000 J kg and the temperature window is 142 K. Additionally, cyano-RbMnFeCo shows barocaloric effects even at low pressures, e.g., reversible adiabatic temperature change is 21 K at 90 MPa. Furthermore, direct measurement of the temperature change using a thermocouple shows +44 K by applying pressure. The temperature increase and decrease upon pressure application and release are repeated over 100 cycles without any degradation of the performance. This material series also possesses a high thermal conductivity value of 20.4 W m K. The present barocaloric material may realize a high-efficiency solid refrigerant.