Effect of alumina content on the crystal structure, lattice thermal expansion and thermal conductivity of aluminium-rich spinel solid solutions

Abstract

Magnesium alumina spinel solid solutions with different chemical compositions were synthesized and their crystal structures were refined using the Rietveld method based on synchrotron radiation X-ray diffraction (XRD). A linear relationship between the lattice parameters a0 and x in Mg1-xAl2+2/3x□1/3xO4 was established, the thermal stability and lattice thermal expansion of the solid solutions by in-situ high temperature XRD were investigated. Alumina was eliminated from the high-solubility alumina-rich spinel solid solution to form corundum and a lower-solubility alumina-rich spinel solid solution. The relationship between a0 and temperature is expressed by a quadratic polynomial. The thermal conductivity of Mg1-xAl2+2/3x□1/3xO4 decreased almost linearly with an increase in x, which is attributed to the stronger point-defect scattering effect induced by the difference in atomic mass and cation radii and the increase in cation vacancies as alumina dissolves in spinel.