Phase equilibria in the low-lithia (< 30 mole% Li 2 O) part of the system Li 2 O-TiO 2 -Ti 2 O 3 have been studied under reducing conditions established by H 2 /CO 2 mixtures. At 1100°C and a H 2 /CO 2 ratio of 70 (fO 2 ؍ 10 ؊16.7 atm), the Li 2 O-TiO 2؊X join comprises alternating one-and two-phase regions in the range 30-6.5 mole% Li 2 O. Single-phase regions occur at compositions centered at :24 mole% Li 2 O (ramsdellite-type, Li 2.2 Ti 3.5 O 8 ) and :13 mole% Li 2 O (1 : 1 ramsdellite : rutile ordered intergrowth, Li 0.9 Ti 2.94 O). By varying the temperature and H 2 /CO 2 ratio, the intergrowth phase was prepared as a single phase in the range 12.8-14.5 mole% Li 2 O. The intergrowth phase reacts readily with air, undergoing both oxidation of Ti 3؉ to Ti 4؉ , and hydroxylation/hydration of lithium in the structure to form LiOH • H 2 O. The reactions with air were quantified using weight gain experiments and Ti 3؉ analyses. The composition region from 6.5 to 0.7 mole% Li 2 O 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 (0kl) r CS phases become unstable relative to a high-temperature, lithium-stabilized anatase phase containing &4 mole% Li 2 O. Powder X-ray, neutron, and electron diffraction techniques have been applied to determine and refine the structures of the different phases.