Probing interface structure and cation segregation in (In, Nb) co-doped TiO2 thin films

Abstract

Atomic-scale exploiting interfacial structure and cation distribution in doped TiO2 thin films possessing a polymorphic structure is of great importance for understanding their film-growth behavior and the structure-property relationship. Here, by applying advanced electron microscopy imaging, we have revealed the atomic-scale microstructure of TiO2 thin films co-doped with In and Nb (TINO) prepared on (001) LaAlO3 substrates by pulsed laser deposition. We determined that the TINO slabs with a brookite-typed structure (B-TiO2) form in the anatase-typed TINO (A-TiO2) film matrix with the crystallographic orientation relationship of (1¯12)[110]A-TiO2//(010)[001]B-TiO2. Besides the polymorphic phase boundary, interface structures including the {112}〈110〉-typed twin boundaries (TBs) in the A-TiO2 films and the (010) stacking faults (SFs) in the B-TiO2 slabs have been characterized. Cation (In and/or Nb) segregation and structure relaxation occur at the TBs and the SFs, which is energetically favorable corroborated by density functional theory calculations. Additionally, the cation segregation in the SFs leads to the formation of a new structure locally. Our findings provide a better understanding of interface structure, cation segregation, and phase formation in the doped-TiO2 polymorph materials.