Barocaloric material

Barocaloric materials are characterized by strong, reversible thermic responses to changes in pressure. Many involve solid-to-solid phase changes from disordered to ordered and rigid under increased pressure, releasing heat. Barocaloric solids under go solid-to-solid phase change.^[1] One barocaloric material processes heat without a phase change: natural rubber.^[2]

Input energy

Barocaloric effects can be achieved at pressures above 200 MPa for intermetallics or about 100 MPa in plastic crystals. However, NH₄I changes phase at pressures of 80 MPa.^[3] The hybrid organic–inorganic layered perovskite (CH₃–(CH₂)n−1–NH₃)₂MnCl₄ (n = 9,10), shows reversible barocaloric entropy change of ΔSr ~ 218, 230 J kg−1 K−1 at 0.08 GPa at 294-311.5 K (transition temperature).^[4]

Barocaloric materials are one of several classes of materials that undergo caloric phase transitions. The others are

Another project used NH₄I as the refrigerant. It achieved reversible entropy changes of ${\displaystyle \Delta {S}_{{P}_{0}\to P}^{\max }}$ ~71 J K⁻¹ kg⁻¹ at ambient temperature. The phase transition temperature is a function of pressure, varying at a rate of ~0.79 K MPa−1. The accompanying saturation driving pressure is ~40 MPa, a barocaloric strength of ${\displaystyle \left|\Delta {S}_{{P}_{0}\to P}^{\max }/\Delta P\right|}$ ~1.78 J K−1 kg−1 MPa−1, and a temperature span of ~41 K under 80 MPa.

• Thermoelectric effect

References