Preparation of stoichiometric and nonstoichiometric magnesium titanate spinels

Polycrystalline samples of stoichiometric spinels, Mg_1+xTi_2-xO₄ (0≤x≤1.0), and spinels with cation diversity, Mg_(1+x)yTi_2-xO₄ and Mg_1+xTi_(2-x)y,O₄ (x=0.4215, y=0.95-1.05), and oxygen deficiency Mg_1+xTi_2-xO_4-δ (x=0.4215, δ=0.05-0.30) were prepared by solid-state reaction of MgO, TiO₂ and Ti to examine the effects of the composition and holding time on the structure of the spinel phase, the impurity phase formation behavior and the electrical properties. In addition to Mg₂TiO₄ (x=1) prepared at 1300°C under an ambient atmosphere, samples were prepared at 1250°C under an argon atmosphere. Compositional analyses revealed that volatilization of compounds and oxidation during firing were negligible. The variation in the unit cell parameter a of the spinel phase indicated solid-solution formation for all stoichiometric samples in spite of the presence of impurities. The impurity-phase formation behavior was strongly dependent upon synthetic conditions, x-value, and induced nonstoichiometry. Other than the insulating Mg₂TiO₄, resistivity measurements indicated that all samples were semiconducting below room temperature. No distinct variation in resistivity behavior was observed for samples with different holding time or with induced nonstoichiometry.