Phase relationships and electrical properties of Ti₃O₅, CrTi₂O₅and the pseudobrookite-type systems Mg_xTi_{3 –x}O₅and Li_xTi_{3 –x}O₅

The structural phase transitions and electrical properties of Ti3O5, the pseudobrookite series LixTi3 –xO5 and MgxTi3 –xO5, and of V3O5 structure type CrTi2O5 have been studied by high-temperature X-ray diffraction, differential scanning calorimetry, and d. c. conductivity measurements. Ti3O5 undergoes a complex transformation between 440 and 515 K from semiconducting α-Ti3O5 to metal-like β′-Ti3O5 with orthorhombic pseudobrookite structure. The intermediate formation of the monoclinic β-Ti3O5 polymorph involves a martensitic transition at 467 K. The following continuous β- to β′-type transition is accompanied by a small polaron order–disorder process. In the series LixTi3 –xO5 and MgxTi3 –xO5 the pseudobrookite-related phases are stabilised. Electrical conductivities are as high as 170 S cm–1 at 1073 K for CrTi2O5. The materials of the MgxTi3 –xO5 series and CrTi2O5 are promising candidates for anodes in solid-oxide fuel cells.