Comment on 'Growth and characterization of tetramethyl ammonium tetrachlorozincate II: A ferroic crystal' by S. Devashankar et al. [J. Cryst. Growth 311 (2009)4207-4212]

摘要

Crystals belonging to the family of the general formula A_2BX_4 have been known for decades and their physical properties have been thoroughly studied. The crystal [N(CH_4)_3]_2ZnCl_4 belongs to this family. With temperature changes it undergoes a number of phase transitions, whose sequence was given for the first time by Sawada et al. [1]: orthorhombic prototype phase of the symmetry Pmcn Z=4-T_1 = 20 ℃, the incommensurate phase with the misfit parameter 5=0.023 along the direction c-T_2 = 6 ℃, orthorhombic ferroelectric phase P2_1cn Z=20-T_3=3.3 ℃, the first ferroelastic phase P112_1 Z=12-T_4=-92 ℃, the second ferroelastic phase P12_1/cl Z=12-T_5=-112 ℃ and the orthorhombic piezoelectric phase P2_12_12_1Z=12 [1].