All-temperature barocaloric effects at pressure-induced phase transitions

Zhao, X.*; Zhang, Z.*; Hattori, Takanori   ; Wang, J.*; Li, L.*; Jia, Y.*; Li, W.*; Xue, J.*; Fan, X.*; Song, R.*; Zhu, J.*; Liu, P.*; Chen, X.-Q.*; Zhang, Z.*; Li, B.*

Caloric effects usually occur in the vicinity of solid-state phase transitions with a limited refrigeration temperature span. Here, we introduce and realize an unprecedented concept -all temperature barocaloric effect, i.e., a remarkable barocaloric effect in KPF across an exceptionally wide temperature span, from 77.5 to 300 K and potentially down to 4 K, covering typical room temperature, liquid nitrogen, liquid hydrogen, and liquid helium refrigeration regions. The directly measured barocaloric adiabatic temperature change reaches 12 K at room temperature and 2.5 K at 77.5 K upon the release of a 250 MPa pressure. This effect is attributed to a persistent phase transition to a rhombohedral high pressure phases. We depict the thermodynamic energy landscape to account for the structural instability. This unique all-temperature barocaloric effect presents a novel approach to highly applicable solid-state refrigeration technology, transcending the conventional multi-stage scenario.