Elastic and anelastic anomalies in (Ca,Sr)TiO3 perovskites:: Analogue behaviour for silicate perovskites

Values of bulk modulus (K), shear modulus (G) and mechanical quality factor (Q) have been determined for polycrystalline samples across the CaTiO3 (CSTO)-SrTiO3 (CST100) solid solution by resonant ultrasound spectroscopy. Because of similarities with low frequency elastic and anelastic anomalies due to twin wall motion reported in previous studies, a working hypothesis is developed in which dissipation processes are interpreted in terms of twin wall displacements. At high temperatures in CST50 the stability field of the 14/mcm structure is marked by the disappearance of all resonance peaks (superattenuation). This is attributed to anelastic domain wall sliding. At room temperature the 14/mcm phase of CST70 and CST80 has values of G which are lower than those of cubic or orthorhombic phases, and a concomitant drop in Q is interpreted as implying that the domain wall pinning process reported elsewhere to occur below similar to 400-450 K is only partial. A similar drop in G and Q was found in CST95 below the Pm (3) over barm <-> 14/mcm transition at similar to 238 K. The 14/mcm <-> Pbcm transition in CST70 at similar to 230 K is marked by an abrupt increase in Q, suggesting that mobile twins in crystals with the 14/mcm structure become effectively immobile in antiferroelectric crystals with the Pbcm structure. The 14/mcm <-> Prima transition in CST50 is marked by a similarly abrupt increase in 0, consistent with twin walls becoming effectively immobile also in crystals with the Pnma structure. A fall in Q below similar to 800 K in CSTO, however, could imply that a degree of twin wall mobility might develop in Prima crystals if the tetragonal spontaneous strain departs significantly from zero. The remarkable attenuation behaviour of crystals with the 14/mcm structure at the relatively low stress conditions which apply during resonances of a parallelepiped with edge dimensions of similar to 2-4 mm, is consistent with the view that a characteristic signature for tetragonal CaSiO3 in the Earth's lower mantle should be a marked attenuation of seismic waves. (C) 2008 Elsevier B.V. All rights reserved.