Microstructural view of anatase to rutile phase transformation examined by in-situ high-temperature X-ray powder diffraction

Abstract

The phase transformation of commercial TiO2 was investigated carefully by in-situ high-temperature X-ray powder diffraction. The diffractograms between 25 ​°C and 800 ​°C were employed to determine the composition, unit cell parameters, and microstructure. The phase transition initiated slowly at 400 ​°C due to the seeding effect of pre-existing rutile and accelerated above 600 ​°C. The unit cell volume of anatase exhibits a third-degree polynomial distribution similar to c-direction, where the volume increased before and decreased during the phase transition. In contrast, a and b unit cell parameters increased with temperature, following a second-degree polynomial distribution. The unit cell parameters and volume of rutile increased continually with temperature following a third-degree polynomial distribution. A slight difference in expansion rates before and during phase transformation reflects the formation and amalgamation of newly materialized rutile with pre-existing one. Both lattice strain and crystallite size of anatase increased before and decreased during the phase transition. The vigorous lattice vibration of the dominant anatase lattice is likely responsible for minor changes in the crystallite shape of pre-existing rutile, resulting in a nominal size decrease before phase transition. The materialization of newly formed rutile occurred under decreased lattice strain and increased crystallite size.