Giant barocaloric effects in sodium hexafluorophosphate and hexafluoroarsenate

Solid-state refrigeration using barocaloric materials is environmentally friendly and highly efficient, making it a subject of global interest over the past decade. Here, we report giant barocaloric effects in sodium hexafluorophosphate (NaPF6) and sodium hexafluoroarsenate (NaAsF6) that both undergo a cubic-to-rhombohedral phase transition near room temperature. We have determined that the low-temperature phase structure of NaPF6 is a rhombohedral structure with space group R3¯ by neutron powder diffraction. There are three Raman active vibration modes in NaPF6 and NaAsF6, i.e., F2g, Eg, and A1g. The phase transition temperature varies with pressure at a rate of dTt/dP = 250 and 310 K GPa−1 for NaPF6 and NaAsF6. The pressure-induced entropy changes of NaPF6 and NaAsF6 are determined to be around 45.2 and 35.6 J kg−1 K−1, respectively. The saturation driving pressure is about 40 MPa. The pressure-dependent neutron powder diffraction suggests that the barocaloric effects are related to the pressure-induced cubic-to-rhombohedral phase transitions. © 2024 AIP Publishing LLC.

Keywords

Sodium, Refrigeration, Materials, Temperature range, Neutrons, Crystallography, Raman spectroscopy, Phase transformations, X-ray diffraction, Chemical composition, Crystal lattices, Refrigerators

Citation

Zhang, Z., Hattori, T., Song, R., Yu, D., Mole, R., Chen, J., He, L., Zhang, Z., & Li, B. (2024). Giant barocaloric effects in sodium hexafluorophosphate and hexafluoroarsenate. Journal of Applied Physics, 136(3). doi:10.1063/5.0211085