Effect of ternary compound on HfO2-Al2O3 mixture coatings revealed by solid-state NMR and TOF-SIMS.

HfO 2 -based mixtures, such as HfO 2 -Al 2 O 3 , play an important role in high-power laser optics and metal oxide semiconductor devices due to their high laser damage resistance and high dielectric constant. However, comprehensive insights into the microstructure and chemical state of HfO 2 -based mixtures at the atomic level are limited, partly because the extremely large fourfold coupling constant of hafnium makes it difficult to characterize. Herein, the Al structures in HfO 2 -Al 2 O 3 mixtures were investigated and compared with that of Al 2 O 3 using solid-state nuclear magnetic resonance (NMR) spectrometry, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and conventional spectroscopic and microscopic techniques. 27Al NMR spectra show that the Al coordination resonances in HfO 2 -Al 2 O 3 mixtures change with the Al content. The content of five-coordinate Al (Al V) is positively correlated with the content of ternary compounds, indicating that the Al–O bonds in ternary compounds tend to be connected at the five-coordinated Al site, which is further demonstrated through annealing experiments of HfO 2 -Al 2 O 3 mixtures. Further, the impact of the above microscopic properties on the macroscopic performance, such as wettability and optical bandgap, has also been explored. Our insights into Al coordination resonances and ternary compounds in HfO 2 -Al 2 O 3 mixtures may help understand the structure–function relationship of mixture coatings. [Display omitted] • The content of ternary compounds in HfO 2 -Al 2 O 3 mixture coatings is affected by mixing ratio and annealing temperature. • Mixing leads to a sharp increase in the content of five-coordinated aluminum. • Changes in the content of five-coordinated aluminum affect the wettability of the coatings. [ABSTRACT FROM AUTHOR]