Researchers from Spain have shown a hybrid perovskite compound that reportedly has great potential in solid-state cooling applications, due to exhibiting giant barocaloric effects near room temperature and under low pressures. Other materials are known to exhibit high caloric effects at room temperature, but many of them require high pressures and are not feasible for commercial applications.
The perovskite material was synthesized through standard wet chemical techniques. To quantify and characterize the material’s caloric effects, the researchers used a combination of X-ray diffraction (XRD, Siemens D-5000 diffractomer), differential scanning calorimetry (DSC, TA Instruments Q2000) and high-pressure DSC (Setaram mDSC7 EVO). They also used a synchrotron PXRD to obtain a Rietveld analysis and calculate the entropy change.
The researchers found a phase transition around 330 K, which involved a complex structural transition with a large response towards pressure and temperature. The material exhibits a perovskite-type structure above and below the transition temperature and the Mn2+ ions form an octahedral array. The ions are bridged by the dicyanamide (dca) ligands to form a 3D network and the tetrapropylammonium (TPrA) cations occupy the pseudo-cuboctahedra holes in the lattice.
The researchers found that even at low pressure, less than 0.007 GPa, and in room temperature environments the material surpasses most of the best caloric materials available today and possess a large caloric effect of 37.0 J kg-1 K-1.
It was found that the entropy change of the hybrid material is determined by the entropic changes of the atomic arrangements that become partly ordered/disordered. As such, the researchers believe there is more room to obtain even greater values by improving the configurational, rotational and vibrational entropies.
The researchers expect follow-up research to include doping, tuning and tailoring of the building blocks, for both this and similar hybrid materials, to achieve an optimized caloric performance. The researchers reckon that this material will not be the only organic-inorganic hybrid material to exhibit such high caloric effects, as many organic-inorganic materials (from MOFs to coordination polymers) have the basic ingredients to produce large caloric effects. As such, this research could open the door to a whole new class of materials to solve a world-wide coolant problem.