Silicate perovskite analogue ScAlO 3: temperature dependence of elastic moduli

Abstract

The elastic moduli of ScAlO 3 perovskite, a very close structural analogue for MgSiO 3 perovskite, have been measured between 300 and 600 K using high precision ultrasonic interferometry in an internally heated gas-charged pressure vessel. This new capability for high temperature measurement of elastic wave speeds has been demonstrated on polycrystalline alumina. The temperature derivatives of elastic moduli of Al 2O 3 measured in this study agree within 15% with expectations based on published single-crystal data. For ScAlO 3 perovskite, the value of (∂ K S/∂ T) P is −0.033 GPa K −1 and (∂ G/∂ T) P is −0.015 GPa K −1. The relative magnitudes of these derivatives agree with the observation in Duffy and Anderson [Duffy, T.S., Anderson, D.L., 1989. Seismic velocities in mantle minerals and the mineralogy of the upper mantle. J. Geophys. Res. 94, 1895–1912.] that |(∂ K S/∂ T) P| is typically about twice |(∂ G/∂ T) P|. The value of (∂ K S/∂ T) P for ScAlO 3 is intermediate between those inferred less directly from V( P, T) studies of Fe-free and Fe- and Al-bearing MgSiO 3 perovskites [Wang, Y., Weidner, D.J., Liebermann, R.C., Zhao, Y., 1994. P– V– T equation of state of (Mg,Fe)SiO 3 perovskite: constraints on composition of the lower mantle. Phys. Earth Planet. Inter. 83, 13–40; Mao, H.K., Hemley, R.J., Shu, J., Chen, L., Jephcoat, A.P., Wu, Y., Bassett, W.A., 1991. Effect of pressure, temperature and composition on the lattice parameters and density of (Mg,Fe) SiO 3 perovskite to 30 GPa. J. Geophys. Res. 91, 8069–8079; Zhang, Weidner, D., 1999. Thermal equation of state of aluminum-enriched silicate perovskite. Science 284, 782–784]. The value of |(∂ G/∂ T)| P for ScAlO 3 is similar to those of most other mantle silicate phases but lower than the recent determination for MgSiO 3 perovskite [Sinelnikov, Y., Chen, G., Neuville, D.R., Vaughan, M.T., Liebermann, R.C., 1998. Ultrasonic shear wave velocities of MgSiO 3 perovskite at 8 GPa and 800K and lower mantle composition. Science 281, 677–679]. Combining the results from the previous studies and current measurements on ScAlO 3 perovskite, we extracted the parameters ( q and γ 0) needed to fully specify its Mie–Grüneisen–Debye equation-of-state. In this study, we have demonstrated that acoustic measurements of K S( T), unlike V( P, T) data, tightly constrain the value of q. It is concluded that ScAlO 3 has ‘normal’ γ 0 (∼1.3) and high q (∼3.6). The high value of q indicates that ScAlO 3 has very strong intrinsic temperature dependence of the bulk modulus; similar behaviour has been observed in measurements on Fe- and Al-bearing silicate perovskites (Mao et al., 1991; Zhang and Weidner, 1999).