Elasticity of CaSnO3 perovskite

The elastic properties of CaSnO3 perovskite have been measured by both ultr asonic interferometry and single-crystal X-ray diffraction at high pressure s. The single-crystal diffraction data collected using a diamond-anvil cell show that CaSnO3 perovskite does not undergo any phase transitions at pres sures below 8.5 GPa at room temperature. Ultrasonic measurements in the mul tianvil press to a maximum pressure of similar to8 GPa at room temperature yielded S- and P-wave velocity data as a function of pressure. For a third- order Birch-Murnaghan EoS the adiabatic elastic moduli and their pressure d erivatives determined from these velocity data are K-S0 = 167.2 +/- 3.1 GPa , K-S0' = 4.89 +/- 0.17, G(0) = 89.3 +/- 1.0 GPa, G(0)' = 0.90 +/- 0.02. Th e quoted uncertainties include contributions from uncertainties in both the room pressure length and density of the specimen, as well as uncertainties in the pressure calibration of the multianvil press. Because the sample is a polycrystalline specimen, this value of K-S0 represents an upper limit t o the Reuss bound (conditions of uniform stress) on the elastic modulus of CaSnO3 perovskite. If the value of alpha gammaT is assumed to be 0.01, the value of K-S0 corresponds to K-T0 = 165.5 +/- 3.1 GPa. The 10 P-V data obtained by single-crystal diffraction were fit with a thir d-order Birch-Murnaghan equation-of-state to obtain the parameters V-0 = 24 6.059 +/- 0.013 Angstrom (3), K-T0 = 162.6 +/- 1.0 GPa, K-T0' = 5.6 +/- 0.3 . Because single-crystal measurements under hydrostatic conditions are made under conditions of uniform stress, they yield bulk moduli equivalent to t he Reuss bound on a polycrystalline specimen. The results from the X-ray an d ultrasonic experiments are therefore consistent. The bulk modulus of CaSnO3 perovskite lies above the linear trend of K-0 wi th inverse molar volume, previously determined for Ca perovskites. This pre vents an estimation of the bulk modulus of CaSiO3 perovskite by extrapolati on. However, our value of Go for CaSnO3 perovskite combined with values for CaTiO3 and CaGeO3 forms a linear trend of G(0) with octahedral tilt angle. This allows a lower bound of 150 GPa to be placed on the shear modulus of CaSiO3 by extrapolation.