A CAS team found a new type of giant BC materials (hexagonal sulfides) and discovered an important role of the electrons in boosting the total entropy change driven by hydrostatic pressure.
This research team was led by Prof. TONG Peng from Institute of Solid State Physics, Hefei Institutes of Physical Science together with Prof. LI Bing from Institute of Metal Research, CAS, and Prof. ZHONG Guohua from Shenzhen Institutes of Advanced Technology, CAS.
In these sulfides Ni1-xFexS (0¡Ü x ¡Ü0.175), the CAS team observed a giant entropy change at room temperature induced by pressure. For instance, an entropy change of around 50 J kg-1 K-1 and a temperature change of ~10 K can be triggered by a small pressure of 100 MPa. Such a high BC performance ranks the current sulfides among the giant BC materials. Based on theoretical calculations and analysis of low-temperature specific heat, the CAS team demonstrated a drastic electronic structural modification and accordingly a large electronic entropy change under pressure, which remarkably facilitate the total BC effect.
More importantly, at the phase transition temperature the thermal conductivity reached 12 W m-1 K-1, which was superior to the values of other BC materials. Particularly, it was two orders of magnitude larger that (0.12 W m-1 K-1) of neopentylglycol which exhibited the strongest BC effect up to date. High thermal conductivity meant high heat-transfer frequency, which was conducive to obtaining high operating frequency and refrigeration power density. So, the excellent BC performance along with superior thermal conductance suggested the current materials are promising refrigerant candidates for solid-state cooling.
This work was supported by Key Research Program of Frontier Sciences, CAS (QYZDB-SSW-SLH015), National Natural Science Foundation of China (U1932127), Users with Excellence Program of Hefei Science Center CAS (No. 2019HSC-UE008), and the Basic Research Program of Shenzhen (Grant No. JCYJ20170818153404696).
Link to the paper: Giant room-temperature barocaloric effect at the electronic phase transition in Ni1-xFexS
A sketch map for the mechanism of giant barocaloric (BC) effect in Ni1-xFexS (up pattern). A comparison of volume normalized entropy change driven by 100 MPa and thermal conductivity (k) for Ni0.85Fe0.15S and other giant BC materials (bottom pattern).(Image by LIN Jianchao)