Dielectric study of ferridistortive phase transition in [N(CH₃)₄]₂MnBr₄ crystals

Abstract

The orthorhombic - monoclinic phase transition at Tc=277. 1K in [N(CH₃)₄]₂MnBr₄ crystals have been studied by measuring dielectric constant along the a, b, and c-axes in the wide range of temperature from 350K to 10K. The anomalous parts of the dielectric constants due to the phase transition are found to show very anomalous temperature dependence. In particular, the anomalous part of the dielectric constant along the c-axis shows broad maximum around 190K and shallow minimum around 120K. The results can be explained on the basis of the two sublattice ferridistortive model. [N(CH₃)₄]₂MnBr₄ is regard as ferridistortive crystal whose spontaneous shear strain consists of two kinds of sublattice strains with the opposite signs and the different magnitude.