Search

The crystal structure of zektzerite, NaLiZrSi6O15, orthorhombic (space group Cmca), consists of six-tetrahedral-repeat corrugated double silicate chains connected into a three-dimensional framework by edge-sharing Li tetrahedral–Zr octahedral chains. At room temperature, the Na+ ions occur at the Na(1) site located within the cylindrical channels created by the corrugation of the silicate double chains. The second sodium site, Na(2), occurs above and below the Zr octahedron and is nominally vacant at room temperature. Above 773 K, vacancies are created at the Na(1) site due to the migration of Na+ ions from the Na(1) to the Na(2) site. Crystal structure refinements at 300, 773, 973, 1223 and 1323 K indicate a progressive increase in the sodium occupancy at the Na(2) site from 0.04 at 773 K to 0.35 at 1323 K. Induced by increasing Na+-ion migration, a first-order high-temperature phase transition occurs above 1123 K as evidenced by a break in the slopes of the thermal expansion curves of the unit cell dimensions and a substantial increase in the electrical conductivity. The unit cell measurements as a function of temperature show marked hysteresis effects during the heating and cooling cycles.

International audience; We report on the lattice dynamics of MgSiO 3 perovskite (bridgmanite). Phonon spectroscopy was performed employing inelastic X-ray scattering from single crystals, and the results were confronted to ab initio calculations. We observe a remarkable agreement between experiment and theory, and provide accurate results for phonon dispersion relations, the vibrational density of states, and the full elasticity tensor. The present work constitutes an important milestone fully validating the lattice dynamics calculation against precise experimental evidence and marks a starting point to extend this kind of combined studies to the high-pressure and high-temperature conditions directly relevant for the physical properties and chemical composition of Earth's lower mantle.