EPR detection and study of new phase transitions in Mg(ClO4)2·6H2O

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Abstract

A temperature dependent EPR study of Mn2+ impurity-doped crystals of Mg(ClO4)2·6H2O has led to the detection of two critical temperatures T1 ~ 335K and T2 ~ 324K where the EPR characteristics undergo distinct changes. The monoclinic distortion of the water octahedron around the metal ion shows little temperature dependence between T1 and T2 and T2 and T3 ~ 272K, while it is found to be comparatively strongly temperature dependent above T1 and below T3, decreasing as T approaches T1 from the high temperature side and as T approaches T3 from the low temperature side. At room temperature the water-perchlorate symmetry seems to deviate slightly from the perfect P63mc symmetry proposed from previous X-ray measurements by West. Although the space symmetry group of the unit cell appears to remain unchanged at T1 and T2, the temperatures T1 and T2 are suspected to be related to structural phase transitions in this crystal.

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    Present address: Department de Chimie Physique, Universite de Geneve, 30 quai Ernest Ansermet, 1211 Geneve 4, Switzerland.

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