Statics and Dynamics of Ferroelectric Domains in Molecular Multiaxial Ferroelectric (Me3NOH)2[KCo(CN)6]

The recent emergence of multiaxial molecular ferroelectrics opens up a new route toward technological evolution in the next-generation flexible/wearable device applications. However, a fundamental understanding of multiaxial ferroelectricity and polarization switching at the microscopic level in these materials is still missing. Herein, we study a high-temperature multiaxial perovskite ferroelectric (Me3NOH)2[KCo(CN)6] (TMC-4) that exhibits a bond-switching phase transition at 417 K with notable piezoelectricity and spontaneous polarization in the ferroelectric phase. The cleavage and reformation of coordination bonds and hydrogen bonds during the bond-switching transition all contribute to a large entropy change of 178.79 J K-1 kg-1 at the phase transition. Using piezoresponse force microscopy (PFM), we observed diverse ferroelectric domain structures and provide evidence for both 180° and non-180° domain switching and their possible effect on the functional properties of molecular ferroelectrics. The results provide an insight into the multiaxial ferroelectricity of TMC-4 at the microscopic level enabling its further use in device applications. © 2021 The Royal Society of Chemistry. This work was supported by the NSFC (22071273, 21805312, and 21821003), and Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01C161). This work (including the grant to W.-J. X.) was also developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, PTDC/CTM-CTM/4044/ 2020 financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The equipment of the Ural Center for Shared Use ‘‘Modern Nanotechnology’’ UrFU was used. The work was supported by the Ministry of Science and Higher Education of the Russian Federation (state task FEUZ-2020-0054). It is also funded by National Funds (OE), through FCT–Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the Article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.