Phase transition in rubidium carnallite doped with VO2+ by EPR method

摘要

This work deals with EPR investigations of VO2+ doped rubidium carnallite. Vanadyl ion in some hosts e.g. NH4Cl and Mg(ClO4).6H2O etc. shows a rotatory behaviour, while in hosts like alums, sulphates, Tutton salts etc., it shows preferential orientation giving angle-dependent spectra. In the present host RbMgCl3.6H2O, the VO2+ shows an isotropic angle independent eight line hyperfine spectrum. It has already been reported that Mn2+ substitutes Mg2+ in NH4MgCl.6H2O giving two distinct EPR spectra having angular variation. But in the present work the spectra of VO2+ in RbMgCl3.6H2O does not show preferred orientation. This behaviour occurs due to VO2+ undergoing a rapid tumbling motion in the crystalline lattice. It has been also found that when the temperature is lowered to LNT, fast reorientations of V-O bond act progressively hindered and the anisotropies in and tensors are not averaged out and get reflected but it is angular independent. After analysing and comparing the spectrum it is found that VO2+ shows ‘liquid like’ behaviour in RbMgCl3.6H2O.