Thermal stability of structure, microstructure and enhanced properties of Zr-Ta-O films with a low and high Ta content

The paper reports on the thermal stability of two ternary Zr-Ta-O films (Zr25Ta5O70, Ta25Zr5O70) and two binary oxide films (ZrO2, Ta2O5) prepared by reactive high-power impulse magnetron sputtering using a pulsed reactive gas flow control. The thermal stability of the structure, microstructure, mechanical and optical properties of the films was investigated in air in the temperature range of 650 °C - 1300 °C. It was found that both ternary Zr-Ta-O films investigated exhibit an enhanced thermal stability of the as-deposited structure and enhanced properties compared to the corresponding binary oxides. The Zr25Ta5O70 film is a single-phase material with a nanocrystalline structure corresponding to the TaZr2.75O8 phase. This phase is stable up to the maximum temperature investigated (1300 °C) and the film retains a high hardness (19 GPa) and refractive index (2.25) even after the annealing to 1000 °C in air. The Ta25Zr5O70 film exhibits an amorphous structure in the as-deposited state with its thermal stability up to 800 °C, which is about 100 °C more than for the Ta2O5 film.