Phase relations and lattice constants in the MgO-Al2O3-Ga2O3 system at 1550 degrees C

Phase relations and lattice constants in the MgO-Al2O3-Ga2O3 system at 1550 degrees C have been determined experimentally. In a large part of this system, only a nonstoichiometric spinel is stable. Compositions as extreme as 12.5 mol% MgO-20.5 mol% Ga2O3-67 mol% Al2O3 for a homogeneous spinel are possible. In the bordering phase diagrams of MgO-Al2O3 and MgO-Ga2O3, the composition of the spinel is as high as 63 mol% Al2O3 or Ga2O3, respectively. The contributions of all simple ionic exchange reactions on the lattice constant of the spinel have been deduced from X-ray diffractometry data.