ELASTICITY OF CATIO3-CASIO3 PEROVSKITES

Polycrystalline specimens in the CaTiO3-CaSiO3 perovskite system have been hot-pressed in a 2000-ton uniaxial split-sphere apparatus (USSA-2 000) at pressures up to 15 GPa and temperature of 1550 degrees C, for the compositions CaTiO3, Ca(Ti0.75Si0.25)O-3, Ca(Ti0.5Si0.5)O-3. For t he specimens with the bulk densities within 1% of the X-ray density, c ompressional and shear wave velocity measurements have been conducted using ultrasonic interferometry. The measured adiabatic bulk moduli (K -s) for the CaTiO3 and Ca(Ti0.5Si0.5)O-3 perovskites are 175(1) and 18 8(1) GPa and shear moduli (G) of 106(1) and 109(1) GPa. In situ X-ray diffraction studies at high pressure and temperature resulted in isoth ermal Values for K-0 of 170(5) and 185(5) GPa, respectively. For the u nquenchable CaSiO3 perovskite, elasticity theory and systematics weft: used to predict K-0=212(7) GPa and G(0)=112(5) GPa; this shear modulu s is 37% less than that for (Mg,Fe)SiO3 perovskite, suggesting that Ca SiO3 perovskite cannot be ignored in modeling the composition of the E arth's lower mantle.