Phase relationships and electrical properties of Ti3O5, CrTi2O5 and the pseudobrookite-type systems MgxTi3 –xO5 and LixTi3 –xO5

Abstract

The structural phase transitions and electrical properties of Ti₃O₅, the pseudobrookite series Li_xTi_{3 –x}O₅ and Mg_xTi_{3 –x}O₅, 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 Li_xTi_{3 –x}O₅ and Mg_xTi_{3 –x}O₅ 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 Mg_xTi_{3 –x}O₅ series and CrTi₂O₅ are promising candidates for anodes in solid-oxide fuel cells.