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 establish ed by H-2/CO2 mixtures, At 1100 degrees C and a H-2/CO2 ratio of 70 (f O(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 re gions occur at compositions centered at similar to 24 mole% Li2O (rams dellite-type, Li2.2Ti3.5O8) and similar to 13 mole% Li2O (1:1 ramsdell ite:rutile ordered intergrowth, Li0.9Ti2.94O), By varying the temperat ure 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 hydro xylation/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 sp anned by series of rutile-derived crystallographic shear (CS) structur es. The CS plane orientation changes continuously with decreasing lith ium content from (051)(r) to (021)(r). At less reducing conditions, th e (Okl)(r) CS phases become unstable relative to a high-temperature, l ithium-stabilized anatase phase containing similar to 4 mole% Li2O. Po wder X-ray, neutron, and electron diffraction techniques have been app lied to determine and refine the structures of the different phases. ( C) 1998 Academic Press.