Pressure-induced shear-mode elastic softening in orthorhombic BaCe_0.85 Y_0.15 O_2.925 perovskite

Abstract

Compressional and shear wave velocities of orthorhombic BaCe_0.85 Y_0.15 O_2.925 perovskite were measured at high pressures up to 8.1 GPa by ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction. At room temperature, the adiabatic bulk modulus increases with increasing pressure, as expected for most polycrystalline materials. The shear modulus, however, show a negative dependence on pressure over a pressure range of ∼2–8.1 GPa. This anomalous elastic softening indicates destabilization of the orthorhombic structure in BaCe_0.85Y_0.15O_2.925 perovskite over the experimental pressure range and is presumably the precursor to the first-order phase transition previously observed at 22 GPa using Raman spectroscopic study.

Keywords:

• perovskite
• ultrasonic interferometry
• X-ray diffraction
• high pressure
• elastic softening

Acknowledgements

This research is supported by the Los Alamos National Laboratory, which is operated by Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396, and by the National Science Foundation under the grant EAR0635860 to BL. The experimental work was carried out at the beamlines X17B2 of the National Synchrotron Light Source of Brookhaven National Laboratory, which is supported by the Consortium for Materials Properties Research in Earth Sciences (COMPRES) under NSF Cooperative Agreement EAR 01-35554. We thank Dr. T. He and Prof. Alex Navrotsky for providing the BaCe_1−xY_xO_3−0.5x perovskite samples.