Phase Transitions and Structures of Phases I, III and IV of (NH₄)₂ZnBr₄

Growth and characterization of undoped, Sr2+-, and Mn2+-doped ammonium tetrachlorozincate

“…Because ZnCl 2 is highly hygroscopic, excess of ZnCl 2 was necessary to compensate the moisture content and to be sure of the chemical stoichiometry. In one case the excess of ZnCl 2 was ~ 2-3 wt % [6], in another case, the excess was as high as ____________________ * Corresponding author: e-mail: mgaafar@aucegypt.edu 10 wt% [7], in a third publication the ratio was 1:1 instead of 2:1 [8][9][10]. Of course, this difference may be attributed to a difference in the moisture content of their ZnCl 2 nevertheless, exact chemical stoichiometry in such cases is only peradventure.…”

Role of NH4 ions in successive phase transitions of perovskite type (NH4)2ZnX4 (X = Cl, Br) by 1H MAS NMR and 14N NMR

“…In phase I (above 432 K), the structure of (NH 4 ) 2 ZnBr 4 is orthorhombic with a o ¼ 7.649Å, b o ¼ 13.353Å, c o ¼ 9.727Å, and space group Pmcn. 21,22 Upon cooling, there is a phase transition at 432 K to an incommensurate phase II that is stable down to 395 K. The structure in phase III, between 395 K and 216 K, is monoclinic with a ¼ a o , b ¼ b o , c ¼ 4c o , b ¼ 90.00(3) , and space group P2 1 / c11. 22 The low-temperature phase IV is orthorhombic with a ¼ a o , b ¼ b o , c ¼ 3c o , and space group P2 1 cn.…”

“…21,22 Upon cooling, there is a phase transition at 432 K to an incommensurate phase II that is stable down to 395 K. The structure in phase III, between 395 K and 216 K, is monoclinic with a ¼ a o , b ¼ b o , c ¼ 4c o , b ¼ 90.00(3) , and space group P2 1 / c11. 22 The low-temperature phase IV is orthorhombic with a ¼ a o , b ¼ b o , c ¼ 3c o , and space group P2 1 cn. 22 The 1 H spin-lattice relaxation times of (NH 4 ) 2 ZnCl 4 and (NH 4 ) 2 ZnBr 4 crystals have been obtained in the laboratory frame by Lim et al [23][24][25] and Ramesh et al, 26 respectively.…”

“…22 The low-temperature phase IV is orthorhombic with a ¼ a o , b ¼ b o , c ¼ 3c o , and space group P2 1 cn. 22 The 1 H spin-lattice relaxation times of (NH 4 ) 2 ZnCl 4 and (NH 4 ) 2 ZnBr 4 crystals have been obtained in the laboratory frame by Lim et al [23][24][25] and Ramesh et al, 26 respectively. The molecular dynamics and phase transitions of (NH 4 ) 2 ZnCl 4 single crystals were reported previously.…”

“…Here, the two inequivalent sites N (1) Fig. 1(b), eight atoms N (11), N (21), N (31), and N(41) are surrounded by ve Cl atoms, while the other atoms N (12), N (22), N (32), and N(42), which are located between the layers created by the ZnCl 4 tetrahedra, are surrounded by eight Cl atoms. From the NMR spectra results of 16 pairs of 14 N, the approximately 32 resonance lines in phases III and IV were measured, as shown in Fig.…”