Dielectric Dispersion in Tris‐Sarcosine Calcium Chloride (TSCC)

Abstract

Abstract Dielectric dispersion of TSCC single crystals of three different qualities is investigated in the frequency range 10 2 to 6 × 10 9 Hz in the close vicinity of T c . Up to three dispersion regions are found where only in the highest frequency one the results are nearly sample independent. They can be roughly fitted to a Debye law where the relaxation frequency obeys the classical critical slowing‐down law fε = A( T  T c ) with A = 0.23 cm −1 K −1 and T c = 130.5 K for 130.7 K < < T < 131.4 K. The results are connected to the far infrared soft‐mode dispersion observed by Kozlov et al. and analyzed using the two‐coupled‐mode model. Although the phase transition is driven by the displacive soft‐mode coordinate, close to T c a strong mixing with a pseudospin relaxing coordinate takes place. The discussion concerning the character of the phase transition in TSCC can be concluded stating that the dynamical origin of the instability leading to the phase transition is overwhelmingly of the displacive type. However, due to the disorder present in the paraelectric structure, the soft‐mode eigenvector becomes temperature dependent near T c and at T c it consists of an equal mixture of both the mode coordinates.