Effect on Local Structure and Phase Transition of Perovskite-Type [N(CH3)4]2Zn1-xCuxBr4 (x = 0, 0.5, 0.7, and 1) Crystals with the Various Doping of Cu2+ Ions

Abstract

This study focused on how the local structures in pure [N(CH₃)₄]₂ZnBr₄ crystal are affected by the partial replacement of Zn²⁺ ions with Cu²⁺ ions. The structures and phase transition temperatures T_C of perovskite-type [N(CH₃)₄]₂Zn_1-xCu_xBr₄ (x = 0, 0.5, 0.7, and 1) mixed crystals were almost unchanged by the partial doping of Cu²⁺ ions. The environments for the local structures of [N(CH₃)₄]₂Zn_1-xCu_xBr₄ mixed systems were studied according to differences in the chemical shifts of the ¹H magic angle spinning (MAS) NMR, ¹³C cross-polarization (CP)/MAS NMR, and ¹⁴N NMR spectra. The ¹H and ¹³C NMR results showed that the local environments of ¹H and ¹³C nuclei near T_C are not affected by substituting Zn²⁺ ions with Cu²⁺ ions, whereas the ¹⁴N NMR results showed that the local environment is affected near T_C. Consequently, the main indicators of the phase transition in [N(CH₃)₄]₂Zn_1-xCu_xBr₄ are related to the ferroelastic characteristics with different orientations.