Microstructural development in nanophase TiO2 during annealing

Abstract

In situ x‐ray‐diffraction studies of nanophase TiO₂ during annealing reveal a strong angular‐dependent decrease in diffuse background intensities and a corresponding increase in rutile and anatase phase peak intensities for samples annealed above 623 K. This behavior is consistent with the crystallization of an amorphous phase present in unannealed samples in addition to the two previously observed crystalline phases. The rutile lattice is significantly strained in unannealed samples, with a₀ increased and c₀ decreased compared to the values for coarse‐grained material. Normal bulk lattice parameters are obtained after annealing samples at 1073 K. Assuming that strain contributions to the measured low‐angle peak breadths are negligible, measurements of the time and temperature dependencies of grain growth in nanophase rutile during annealing indicate a grain growth exponent of 0.64±0.06 and a grain growth activation enthalpy of 83±40 kJ/mol.