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  Scott, J.F.; Bryson, J.; Carpenter, M.A.; Herrero-Albillos, J.; Itoh, M.: Elastic and anelastic properties of ferroelectric SrTi¹⁸O₃ in the kHz-MHz regime. Physical Review Letters 106 (2011), p. 105502/1-4

10.1103/PhysRevLett.106.105502

Abstract:
Resonant ultrasound spectroscopy has been used to follow elastic softening in SrTi18O3 in the frequency range
0:2–1 MHz. A dramatic softening of C44 occurs as the Curie temperature Tc ¼ 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 ðC11  C12 Þ. 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.