Elastic and anelastic properties of ferroelectric SrTi(18)O3 in the kHz-MHz regime

Resonant ultrasound spectroscopy has been used to follow elastic softening in SrTi(18)O3 in the frequency range ∼0.2-1  MHz. A dramatic softening of C44 occurs as the Curie temperature T(c) = 24  K is approached from above or below, which correlates with the development of a central peak in Raman and Brillouin spectra. This is attributed to strong coupling between the acoustic mode and the central peak mode. A weaker anomaly is seen in a resonance mode which is believed to be controlled by 1/2(C11-C12). Significant attenuation accompanies this softening and an additional dissipation peak has also been observed at ∼80-90  K. This extends earlier work by a factor of 150,000× from the 30 GHz regime and helps address the question as to whether the ferroelectricity is stimulated primarily by a soft mode into a homogeneous ground state or by clustering of rhombohedral nanoregions into an inhomogeneous ground state.