Relation between Phonon Structure and Phase Transition in NaClO3

Single crystals of NaCl${\mathrm{O}}_3$ have been investigated to understand their ferroelectric behavior. Our investigations show that a number of transverse optic modes in the low-frequency region vary in frequency as the transition temperature is approached. The product of the squares of the frequencies of these modes varies as $T-T_c$ with $T_c\approx 576$°K. This may be a general description of Cochran's soft-mode theory in which the lowest optic mode has all the temperature dependence.