Cation dopant effect on phase transformation and microstructural evolution in M2+-substituted c-alumina powders

The effect of divalent cation dopants on the phase transformation and microstructural evolution in M2+- substituted c-alumina (GA-M; M = Mg, Ca, Sr, Mn, Co, Ni, Cu, Zn; 0.1–0.5 mol%) powders were systematically investigated. Divalent cations were substituted into the defect spinel lattice of c-alumina through a sol–gel route using high-purity polyhydroxoaluminum and MCl2 solutions. All divalent dopants retarded c-to-a transformation up to 0.3 mol%. A correlation was found between the transformation temperature and the ionic radius of dopant at 0.5 mol% with the exception of the Cu series, where eutectic liquid formation may occur. The microstructural evolution in GA-M powders at high temperature was strongly affected by dopants that segregated from GA-M primary particles to the grain boundary during/after transformation. All dopant effects on grain growth in GA-M powders at 0.1 mol% were retarding. Average grain size at high temperatures seemed to correlate with dopant ionic radius, excepting Cu and Mn.