Colossal Barocaloric Effect in Carboranes as a Performance Tradeoff

The discovery of colossal barocaloric effects in organic plastic crystals has significantly advanced the development of solid-state refrigerant techniques. Adapting to the real application, a tradeoff of various barocaloric performances has to be achieved. Here, it is reported a novel plastic crystal system, that is, carboranes (C2B10H12), including three positional isomers: ortho-carborane, meta-carborane, and para-carborane, which are characterized by C-2v, C-2v, D-5d point groups, respectively. They all undergo an orthorhombic-to-tetragonal phase transition around room temperature. Compared to the previously reported organic plastic crystals, this system exhibits a combination of large pressure-normalized entropy changes, the high-pressure sensitivity of the transition temperature, small thermal hysteresis, and so forth. Their barocaloric performances are positional-isomerism dependent, and the best performances are obtained in para-carborane with maximum entropy changes of about 106.2 J kg(-1) K-1 achieved under pressure changes below 30 MPa. This study not only suggests that carboranes would be a considerably promising working material for barocaloric refrigeration at room temperature but also indicates that delicate tuning of molecular isomerism is an effective strategy to enhance barocaloric performances.

Automated summary

A novel plastic crystal system, carboranes (C2B10H12), with large barocaloric effects around room temperature, has been reported. The study suggests that delicate tuning of molecular isomerism is an effective strategy to enhance barocaloric performances.