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

Abstract

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 (19GPa) 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.