Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals

Pritam Sadhukhan,Yoshihito Shiota,Michael L Baker,Kaoru Yamamoto,Takumi Nakanishi,Thomas Kroll,Jeremy Ian Long,Shinji Kanegawa,Osamu Sato,Shu-Qi Wu,Norimichi Kojima,Kaige Gao,Akira Sakamoto,Hajime Okajima,Kazunari Yoshizawa,Atsushi Okazawa,Dimosthenis Sokaras

doi:10.1038/s41467-021-25041-4

Abstract

Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. However, obtaining materials with large and nearly constant pyroelectric coefficients over a wide temperature range for practical uses remains a formidable challenge. Attempting to discover a solution to this obstacle, we combined molecular design of labile electronic structure with the crystal engineering of the molecular orientation in lattice. This combination results in electronic pyroelectricity of purely molecular origin. Here, we report a polar crystal of an [FeCo] dinuclear complex exhibiting a peculiar pyroelectric behavior (a substantial sharp pyroelectric current peak and an unusual continuous pyroelectric current at higher temperatures) which is caused by a combination of Fe spin crossover (SCO) and electron transfer between the high-spin Fe ion and redox-active ligand, namely valence tautomerism (VT). As a result, temperature dependence of the pyroelectric behavior reported here is opposite from conventional ferroelectrics and originates from a transition between three distinct electronic structures. The obtained pyroelectric coefficient is comparable to that of polyvinylidene difluoride at room temperature.

Highlights

Pyroelectricity plays a crucial role in modern sensors and energy conversion devices
At approximately 90 K, an abrupt spin transition from Fe3+LS to Fe3+HS occurs (LS = low spin, HS = high spin) which is followed by a temperatureinduced continuous population change between the two redox isomers, C[Fe3+HS–dhbq3−–Co3+LS] and C[Fe2+HS–dhbq2−–Co3+LS], a phenomenon known as valence tautomerism (VT)
These results suggest that the selective crystallization of an [FeCo] heterometallic dinuclear complex occurs

Summary

Introduction

Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. Pyroelectric effect emerges because of two distinct electronic dynamics, i.e. the change in spin and charge distribution in the polar [FeCo] crystal.

Results

Conclusion