Aem Investigation of Tetrahedrally Coordinated TI4+ in Nickel-Titanate Spinel

Abstract

ABSTRACTThe stoichiometry and site distribution of metastable nickel-titanate spinel has been studied with AEM. The results of EDXS and EELS agree that the metastable spinel is nonstoichiometric and titanium-deficient relative to its hypothetical endmember composition, “Ni2TiO4”. The titanium deficiency has been determined by EELS to be Δ = 0.025 ± 0.005. Channeling-enhanced microanalysis and ELNES studies indicate that the Ti4+ and Ni2+ cations are in tetrahedral and octahedral coordination, respectively, so that the metastable spinel has the normal cation distribution: Til−Δ[Ni2(1+Δ)]O4. This result is consistent with neutron powder-diffraction studies and SiO2-solubility measurements of similar equilibrated and quenched spinel-containing specimens. Metastable nickel-titanate spinel therefore contrasts with stable stoichiometric spinels which tend to the inverse cation distribution, Me[MeTi]O4.