Giant barocaloric effects at low pressure in ferrielectric ammonium sulphate.

P Lloveras,S Crossley,N D Mathur,J.-Ll Tamarit,M Barrio,E Stern-Taulats,W Li,Ll Mañosa,A Planes,X Moya,V Pomjakushin

doi:10.1038/ncomms9801

Abstract

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Most of the research is centred on large magnetocaloric effects and large electrocaloric effects, but the former require large magnetic fields that are challenging to generate economically and the latter require large electric fields that can only be applied without breakdown in thin samples. Here we use small changes in hydrostatic pressure to drive giant inverse barocaloric effects near the ferrielectric phase transition in ammonium sulphate. We find barocaloric effects and strengths that exceed those previously observed near magnetostructural phase transitions in magnetic materials. Our findings should therefore inspire the discovery of giant barocaloric effects in a wide range of unexplored ferroelectric materials, ultimately leading to barocaloric cooling devices.

Highlights

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications
Effects driven by hydrostatic pressure near phase transitions have only been observed in a small number of relatively expensive magnetic materials, where changes of magnetization are accompanied by changes in crystal symmetry[4,5] or volume alone[6,7,8] (Table 1). (Large BC effects have been observed in poly(methyl methacrylate) away from any transition9.) Here we demonstrate giant BC effects near the ferrielectric phase transition[10,11,12,13] in a powder of ammonium sulphate (AS)
We use calorimetry to identify pressure-driven isothermal entropy changes of |DS|B60 J K À 1 kg À 1, which exceed the corresponding values that have been found for metallic alloys near first-order magnetic phase transitions (B10–25 J K À 1 kg À 1; Table 1), and predicted for PbTiO3 ferroelectric phase transitions[14,15] a(Bnd3B–4aTJ iKOÀ3 near first-order 1 kg À 1)

Summary

Introduction

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Integration of (dQ/dT)/T yields the corresponding entropy change DS(T) (Fig. 1c), with |DSf| 1⁄4 130±6 J K À 1 kg À 1 for the full transition. On heating through the ferrielectric transition, X-ray diffraction data confirm the expected changes in crystal structure[10,11,13].

Results

Conclusion