Influence of Cu doping on the phase transformation and microstructure of zinc titanate thin films by RF magnetron sputtering

The influence of Cu doping on the properties, phase transformation and microstructure of ZnTiO₃ films was investigate. Experiments were performed with Cu depositing on ZnTiO₃ ceramic targets by RF magnetron sputtering at substrate temperatures, and by controlling the Cu content, different Cu-doped ZnTiO₃ films were deposited on SiO₂/Si substrates. ESCA analysis shows that the mass fractions of Cu in the Cu-doped ZnTiO₃ films are 0. 84%, 2. 33%, and 2. 84%. XRD analysis reveals that the Cu-doped ZnTiO₃ films are amorphous at normal temperature;
after annealed at 600℃ the films transforms from amorphous to Zn₂Ti₃O₈ crystalline phase, but there is no crystalline phase in the pure ZnTiO₃ film annealed at 600℃. The Zn₂Ti₃O₈ phase decomposes into Zn₂TiO₄ phase and TiO₂ phase, and the lattice of ZnTiO₃ changes little because the Zn²⁺ position is replaced by Cu ions when annealing at 900℃. XRD, SEM and TEM analyses show that the formation of TiO₂ phase would be inhibited when doping too much Cu. When Cu²⁺ substitutes for Zn²⁺ in an ABO₃ structure, it leads to the formation of twin-crystals which is attributed to the lattice strain. This result can be confirmed by TEM analysis. With the precipitation of excessive Cu, the average grain size gradually becomes small and the lattice strain is also decreased, so that the lattice constant returns to the original level.