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

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 a 0 and x in Mg 1- x Al 2+2/3 x □ 1/3 x O 4 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 a 0 and temperature is expressed by a quadratic polynomial. The thermal conductivity of Mg 1- x Al 2+2/3 x □ 1/3 x O 4 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.