Effects of paramagnetic interactions by the partial replacement of Zn2+ ions with Cu2+ ions in lead-free zinc-based perovskite (MA)2ZnCl4 crystal by MAS NMR

The growths, structures, phase transition temperatures, and molecular dynamics of mixed (MA)2Zn1-xCuxCl4 (x=0, 0.3, 0.5, 0.7, and 1) crystals were investigated to understand the effect of the random presence of paramagnetic Cu2+. In addition, the spin-lattice relaxation time T1ρ in the rotating frame by the magic angle spinning nuclear magnetic resonance (MAS NMR) method was obtained for 1H and 13C nuclei to understand the molecular dynamics for varying amounts of Cu2+ ions. The structure and phase transition temperature for the case where x=0.3 was similar to those for x=0, whereas those of x=0.5 and 0.7 were similar to those for x=1. Although the crystal structures and phase transition temperatures were similar for x (=0 and 0.3), and x (=0.5, 0.7, and 1), the molecular motions of 1H and 13C for x=0.3 differed from those for x=0, 0.5, 0.7, and 1. We compared the activation energies Ea by the molecular motions for 1H and 13C, based on the T1ρ. The Cu2+ presence for x=0.3 in the mixed structure indicates any differences in the Ea for 1H and 13C, and the replacement of Zn2+ ions by Cu2+ ions for x=0.3 was strongly affected by the molecular motions.