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Title: Driving Barocaloric Effects in a Molecular Spin-Crossover Complex at Low Pressures
Barocaloric effectsthermal changes in a material induced by applied hydrostatic pressureoffer promise for creating solid-state refrigerants as alternatives to conventional volatile refrigerants. To enable efficient and scalable barocaloric cooling, materials that undergo high-entropy, reversible phase transitions in the solid state in response to a small change in pressure are needed. Here, we report that pressure-induced spin-crossover (SCO) transitions in the molecular iron(II) complex Fe[HB(tz)3]2 (HB(tz)3− = bis[hydrotris(1,2,4-triazol-1-yl)borate]) drive giant and reversible barocaloric effects at easily accessible pressures. Specifically, high-pressure calorimetry and powder X-ray diffraction studies reveal that pressure shifts as low as 10 bar reversibly induce nonzero isothermal entropy changes, and a pressure shift of 150 bar reversibly induces a large isothermal entropy change (>90 J kg−1 K−1) and adiabatic temperature change (>2 K). Moreover, we demonstrate that the thermodynamics of the SCO transition can be fine-tuned through systematic deuteration of the tris(triazolyl)borate ligand. These results provide new insights into pressure-induced SCO transitions and further establish SCO materials as promising barocaloric materials.  more » « less
Award ID(s):
2011754
PAR ID:
10501562
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
ACS
Date Published:
Journal Name:
Journal of the American Chemical Society
Volume:
144
Issue:
14
ISSN:
0002-7863
Page Range / eLocation ID:
6493 to 6503
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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