New phases formed in the Li-Ti-O system under reducing conditions

Phase equilibria in the low-lithia (<30 mole% Li2O) part of the system Li2O-TiO2-Ti2O3 have been studied under reducing conditions established by H-2/CO2 mixtures, At 1100 degrees C and a H-2/CO2 ratio of 70 (fO(2) = 10(-16.7) atm), the Li2O-TiO2-x join comprises alternating one- and two-phase regions in the range 30-6.5 mole% Li2O, Single-phase regions occur at compositions centered at similar to 24 mole% Li2O (ramsdellite-type, Li2.2Ti3.5O8) and similar to 13 mole% Li2O (1:1 ramsdellite:rutile ordered intergrowth, Li0.9Ti2.94O), By varying the temperature and H-2/CO2 ratio, 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)(r) to (021)(r). At less reducing conditions, the (Okl)(r) CS phases become unstable relative to a high-temperature, lithium-stabilized anatase phase containing similar to 4 mole% Li2O. Powder X-ray, neutron, and electron diffraction techniques have been applied to determine and refine the structures of the different phases. (C) 1998 Academic Press.