New Phases Formed in the Li–Ti–O System under Reducing Conditions

Abstract

Phase equilibria in the low-lithia (<30 mole% Li2O) part of the system Li2O–TiO2–Ti2O3have been studied under reducing conditions established by H2/CO2mixtures. At 1100° C and a H2/CO2ratio of 70 (fO2=10−16.7atm), the Li2O–TiO2−Xjoin comprises alternating one- and two-phase regions in the range 30–6.5 mole% Li2O. Single-phase regions occur at compositions centered at ∼24 mole% Li2O (ramsdellite-type, Li2.2Ti3.5O8) and ∼13 mole% Li2O (1:1 ramsdellite:rutile ordered intergrowth, Li0.9Ti2.94O). By varying the temperature and H2/CO2ratio, the intergrowth phase was prepared as a single phase in the range 12.8–14.5 mole% Li2O. The intergrowth phase reacts readily with air, undergoing both oxidation of Ti3+to Ti4+, and hydroxylation/hydration of lithium in the structure to form LiOH·H2O. The reactions with air were quantified using weight gain experiments and Ti3+analyses. The composition region from 6.5 to 0.7 mole% Li2O is spanned by series of rutile-derived crystallographic shear (CS) structures. The CS plane orientation changes continuously with decreasing lithium content from (051)rto (021)r. At less reducing conditions, the (0kl)rCS phases become unstable relative to a high-temperature, lithium-stabilized anatase phase containing ∼4 mole% Li2O. Powder X-ray, neutron, and electron diffraction techniques have been applied to determine and refine the structures of the different phases.