Ultrasensitive barocaloric material for room-temperature solid-state refrigeration

Abstract

Abstract One of the greatest obstacles to the real application of solid-state refrigeration is the huge driving fields. Here, we report a giant barocaloric effect in inorganic NH 4 I with reversible entropy changes of $$\Delta {S}_{{P}_{0}\to P}^{{{\max }}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>→</mml:mo> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ∼71 J K −1 kg −1 around room temperature, associated with a structural phase transition. The phase transition temperature, T t , varies dramatically with pressure at a rate of d T t /d P ∼0.79 K MPa −1 , which leads to a very small saturation driving pressure of Δ P ∼40 MPa, an extremely large barocaloric strength of $$\left|\Delta {S}_{{P}_{0}\to P}^{{{\max }}}/\Delta P\right|$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>→</mml:mo> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>/</mml:mo> <mml:mi>Δ</mml:mi> <mml:mi>P</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> ∼1.78 J K −1 kg −1 MPa −1 , as well as a broad temperature span of ∼41 K under 80 MPa. Comprehensive characterizations of the crystal structures and atomic dynamics by neutron scattering reveal that a strong reorientation-vibration coupling is responsible for the large pressure sensitivity of T t . This work is expected to advance the practical application of barocaloric refrigeration.

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