Effect on Local Structure and Phase Transition of Perovskite-Type [N(CH 3 ) 4 ] 2 Zn 1-x Cu x Br 4 (x = 0, 0.5, 0.7, and 1) Crystals with the Various Doping of Cu 2+ Ions.

This study focused on how the local structures in pure [N(CH ₃ ) ₄ ] ₂ ZnBr ₄ crystal are affected by the partial replacement of Zn ²⁺ ions with Cu ²⁺ ions. The structures and phase transition temperatures T _C of perovskite-type [N(CH ₃ ) ₄ ] ₂ Zn _1-x Cu _x Br ₄ (x = 0, 0.5, 0.7, and 1) mixed crystals were almost unchanged by the partial doping of Cu ²⁺ ions. The environments for the local structures of [N(CH ₃ ) ₄ ] ₂ Zn _1-x Cu _x Br ₄ mixed systems were studied according to differences in the chemical shifts of the ¹ H magic angle spinning (MAS) NMR, ¹³ C cross-polarization (CP)/MAS NMR, and ¹⁴ N NMR spectra. The ¹ H and ¹³ C NMR results showed that the local environments of ¹ H and ¹³ C nuclei near T _C are not affected by substituting Zn ²⁺ ions with Cu ²⁺ ions, whereas the ¹⁴ N NMR results showed that the local environment is affected near T _C . Consequently, the main indicators of the phase transition in [N(CH ₃ ) ₄ ] ₂ Zn _1-x Cu _x Br ₄ are related to the ferroelastic characteristics with different orientations.