抄録
Anisotropy and temperature dependence of elastic constants of phenothiazine crystal, which undergoes a ferroelastic phase transition at Tc=248.8 K, were obtained by ultrasonic velocity measurements. The characteristic anisotropy of this crystal against shear stress is suggested to have a relation to weak intermolecular hydrogen bonds extended along b-axis. A phenomenological analysis of free energy of the crystal indicates that the novel temperature dependence exhibited by the elastic constant C33 arises from a coupling of the strain e3 with the strain e5 along which a softening is observed as the temperature approaches Tc. Temperature dependence of the spontaneous deformation in the low-temperature phase and the entropy of transition are qualitatively explained in terms of the above analysis.
