EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

Abstract

X-band electron paramagnetic resonance investigations of single crystals of Cr-doped dimethylammonium gallium sulphate hexahydrate are presented from room temperature down to 110 K. The crystal undergoes a order–disorder phase transition to ferroelectric phase at 134 K and additionally a first-order transition into a low temperature non-ferroelectric phase at Tc2 = 116 K. The spin-Hamiltonian parameters were determined for paraelectric and ferroelectric phases. The spin-Hamiltonian parameters in the paraelectric phase are: g = 1.982± 0.002, b2 = (890± 10)× 10−4 cm−1, b = (386 ± 15) × 10−4 cm−1. Remarkable EPR line width changes confirm the order–disorder character of the ferroelectric phase transition. Additionally observed triplet lines demonstrate freezing-out of dimethylammonium reorientations which can be considered as a prime reason for this transition similarly as observed in dimethylammonium aluminium sulfate hexahydrate.