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Abstract
The orthorhombic-monoclinic phase transition at Tc = 287.6 K in [N(CH3)4]2ZnBr4 crystal has been studied by measuring the deviation angle Δβ(T) = β(T) - 90° of monoclinic angle β(T) from 90° and the dielectric constants ϵ'(T) along the a-, b- and c-axes. The deviation angle Δβ(T) rapidly increases just below TC, and takes maximum value and then shows gradually decrease down to 28 K. The deviation angle Δβ(T) becomes zero at TZ = 117 K and then becomes negative. The anomalous parts of dielectric constants due to the phase transition show very anomalous temperature dependence. The two sublattice ferridistortive model can qualitatively explain the anomalous temperature dependence of both the deviation angle Δβ(T) and the dielectric constant. [N(CH3)4]2ZnBr4 crystal can be regarded as a ferridistortive crystal just as in case of [N(CH3)4]2CoBr4 and [N(CH3)4]2MnBr4 crystals.