Thermal Expansivity and Ultrasonic Propagation Near the Structural Transition of SrTiO3

The thermal expansivity and ultrasonic response of SrTi${\mathrm{O}}_3$ have been studied in the vicinity of its structural transition. The nature of the expansivity discontinuity indicates that the transition is second order and that the temperature region in which critical fluctuations are appreciable is less than the strain-broadened transition width. The ultrasonic behavior near $T_a$ is complex and appears to be dominated by structural inhomogeneities.