PHASE-RELATIONSHIPS AND ELECTRICAL-PROPERTIES OF TI3O5, CRTI2O5 AND THE PSEUDOBROOKITE-TYPE SYSTEMS MGXTI3-XO5 AND LIXTI3-XO5

The structural phase transitions and electrical properties of Ti3O5, the pseudobrookite series LixTi3-xO5 and MgxTi3-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 alpha-Ti3O5 to metal-like beta'-Ti3O5 with orthorhombic pseudobrookite structure. The intermediate formation of the monoclinic beta-Ti3O5 polymorph involves a martensitic transition at 467 K. The following continuous beta- to beta'-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.