Analysis of Raman Spectra of the Overdamped Mode in KH_2(1−x)D_2xPO₄ Crystals with Single-Mode Line Shape Functions

Abstract

The Raman spectra of an overdamped B₂-mode in KH_2(1−x)D_2xPO₄ crystals have been analyzed with the generalized form of single-mode susceptibility. It has been shown that the absolute value of a pole \ ildeω₁ of χ(ω) which makes a larger contribution to the line shape, e.g., in case of a damped harmonic oscillator, a pole closest to the origin, is the most appropriate parameter to describe the phase transition regardless of the model adopted in the analysis. The |ω₁| was proved to have a linear temperature dependence for any x in the neighborhood of T_c. It is suggested that there exists a critical degree of deuteration x_c≅0.2, at which the mechanism of the phase transition changes qualitatively.