Phase transformations and microstructures of TiO2–SnO2 due to solution annealing versus reactive sintering

TiO2–SnO2 in molar ratios of 2:8, 5:5 and 8:2 were subject to solution annealing, or alternatively prepared by a reactive sintering route, for X-ray diffraction and analytical electron microscopic studies. Defect clusters and commensurate superstructures were formed in the TiO2–SnO2 solid solution of the rutile-type structure when quenched from 1600 °C in air. Upon annealing and decomposition outside the spinodal at 1000 °C, a metastable ilmenite-type phase was precipitated from the rutile structure. This is in drastic contrast to the spinodal decomposition along [0 0 1] to form a semi-coherent (0 0 1) interface. An alternative phase-equilibrium route by reactive sintering at 1000 °C was facilitated by rapid interdiffusion and Brownian rotation of smaller-sized SnO2 particles until parallel epitaxial relationship with the TiO2-rich host was reached.