EPR Study of the Phase Transition in Dimethylammonium Gallium Sulfate Hexahydrate

Abstract

X-band electron paramagnetic resonance investigations of single crystals of Cr3+ -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 T c2 = 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, b 0 2 = (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.

EPR study of local ordering in DMAAlS and DMAGaS crystals

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