Impact of the Copper-Induced Local Framework Deformation on the Mechanism of Structural Phase Transition in [(CH3)2NH2][Zn(HCOO)3] Hybrid Metal–Formate Perovskite

Abstract

Dimethylammonium zinc formate [(CH3)2NH2][Zn(HCOO)3] (DMAZn) treated as a model dense metal–organic framework is a compound that has been intensively studied in the last decade. It undergoes a first-order order–disorder structural phase transition at T0 ∼ 167K, considered as the improper ferroelectric one. The complex mechanism of this phase transition is attributed to the ordering of the hydrogen bonds between (CH3)2NH2+ (DMA+) and the formate groups as well as distortion of the zinc–formate framework. Here, the analysis of the impact of zinc substitution by Cu doping on the order–disorder phase transition is presented. The Jahn–Teller effect of Cu2+ ions results in a local framework distortion, which consequently perturbs the structural dynamics. Based on the dielectric, thermal, structural, electron paramagnetic resonance, and IR spectroscopy measurements, it is shown that doping with Cu2+ ions leads to a decrease of the phase transition entropy and temperature as well as a change in the nature of the ...