Dielectric, calorimetric and elastic anomalies associated with the first order [Formula: see text] phase transition...

Conduction calorimetry has been used to determine with high precision the latent heat and variation in heat capacity which accompany the first order [Formula: see text] phase transition in perovskites with compositions (Ca(1-x)Sr(x))TiO(3), x = 0.65, 0.68, 0.74 (CST65, CST68, CST74). In CST65 (CST68), the latent heat is dissipated/absorbed over a temperature interval of ∼11 K (∼6 K), which is centred on ∼292 K (∼258 K) during cooling and ∼302 K (∼270 K) during heating. The magnitude of the latent heat diminishes with increasing SrTiO(3) content and was not detected in CST74. Integration of the latent heat and excess heat capacity yields small excess entropies, which are consistent with the structural changes being displacive rather than order-disorder in origin. Resonant ultrasound spectroscopy measurements on the same CST65 sample as used for dielectric and calorimetric measurements through the same temperature intervals have allowed quantitative correlations to be made with the bulk modulus, shear modulus and acoustic dissipation parameter, Q(-1). The dielectric anomaly and changes in Q(-1) can be understood as being linear combinations of the properties of the separate I4/mcm and Pbcm phases in proportion to their volume fractions across the two-phase field. A change of only ∼0.5-1 GPa has been detected in the bulk modulus but the shear modulus softens by ∼5-8 GPa as the transition interval is approached from above and below. This shear mode softening presumably reflects clustering and/or phonon softening in both the I4/mcm and Pbcm structures. This pattern of structure-property relations could be typical of first order transitions in perovskites where there is no group/subgroup relationship between the high and low symmetry phases.