Elasticity of aluminate,titanate, stannate and germanate compounds with the perovskite structure

Ultrasonic data for the velocities of a large number of perovskite-structure compounds have been determined as a a function of pressure to 6 kbar at room temperature for polycrystalline specimens hot-pressed at pressures up to 100 kbar in solid-media devices: ScAlO₃, GdAlO₃, SmAlO₃, EuAlO₃, YAlO₃, CdTiO₃, CdSnO₃, CaSnO₃ and CaGeO₃. The elasticity data for these orthorhombic and cubic perovskites define systematic patterns on bulk modulus (K_S)-volume (V_O) and bulk sound velocity (υ_φ—mean atomic weight (M) diagrams which are insensitiv to the details of cation chemistry and crystallographic structure. These isostructural trends are used to estimate K_S = 2.5 ± 0.3 Mbar and υ_φ = 7.9 ± 0.4 km/s for the perovskite polymorph of MgSiO₃. On a Birch diagram of veloc vs. density, the perovskite data define linear trends which lead to erroneous estimates of velocity for MgSiO₃ unless specific account is taken of ionic radius effects in isomorphic substitutions.