Solid-state diffusive amorphization in TiO2/ZrO2 bilayers

Thin films of crystalline TiO2 were deposited on self-assembled organic monolayers from aqueous TiCl4 solutions at 80 C; partially crystalline ZrO2 films were deposited on top of the TiO2 layers from Zr(SO4)2 solutions at 70 C. In the absence of a ZrO2 film, the TiO2 films had the anatase structure and underwent grain coarsening on annealing at temperatures up to 800 C; in the absence of a TiO2 film, the ZrO2 films crystallized to the tetragonal polymorph at 500 C. However, the TiO2 and ZrO2 bilayers underwent solid-state diffusive amorphization at 500 C, and ZrTiO4 crystallization could be observed only at temperatures of 550 C or higher. This result implies that metastable amorphous ZrTiO4 is energetically favorable compared to two-phase mixtures of crystalline TiO2 and ZrO2, but that crystallization of ZrTiO4 involves a high activation barrier