Strong biaxial texture and polymorph nature in TiO2 thin film formed by ex-situ annealing on c-plane Al2O3 surface

► TiO2 films grown at room temperature on (0001) Al2O3 and annealed ex-situ. ► Rutile shows one and anatase three types of in-plane orientations within single film. ► Epitaxial relationship of rutile: R(100)[001]‖sub(0001)[11̄00]. ► Epitaxial relationship of anatase: A(001)[110]‖sub(0001)[11̄00]. ► In addition, A(112)‖sub(0001) anatase showed two options A[11̄0]‖sub[11̄00] and A[11̄0]‖sub[21̄1̄0].