A Phenomenological Theory of the Huang Scattering of Light Near Structural Phase Transition Temperatures

Abstract

A simple phenomenological theory is presented to discuss the origin of elastic “central peaks” observed near structural phase transition temperatures by light scattering. The scattering intensity I_C of light from the polarization induced around a charge impurity is formulated on the analogy of the Huang scattering of X-rays. The dependence of I_C on the direction of the scattering wave vector and temperature has been numerically computed and is found to reproduce well the experimental results in KD₂PO₄. The theory is shown to be applicable to the “central peak” due to the strain induced around an elastic defect observed in KH₂PO₄ or KH_3(1−x)D_3x(SeO₃)₂.