Effect of B2O3 addition to Magnesium, Zirconium, Hafnium fluorides on the parameters of thin films formed from them

Abstract

For the first time, the influence of a B2O3 additive on Magnesium, Zirconium, and Hafnium fluorides, encompassing their structural and optical properties, was subjected to investigation. The phase composition of the MgF2–B2O3 system was ascertained through the utilization of X-ray phase analysis and infrared (IR) transmission spectroscopy. Notably, a discernible presence of a newly formed phase, characterized as a complex compound of Magnesium fluoroborate (Mg3(BO3)F3), was unveiled. In the instances of the ZrF4–B2O3 and HfF4–B2O3 systems, the modification in the characteristics of IR spectra was attributed to the α → β phase transitions occurring within the respective metal tetrafluorides. Subsequently, thin-film coatings of metal fluorides treated with the B2O3 additive were fabricated employing thermal evaporation under vacuum conditions. It was determined that the refractive index of MgF2 experienced a slight reduction (from 1.42 to 1.41) following the incorporation of the additive, while the mechanical strength exhibited a marginal augmentation. Conversely, the refractive index of coatings derived from Zirconium and Hafnium tetrafluorides, subsequent to heat treatment with B2O3, remained nearly constant at 1.53 across all samples. Additionally, an evaluation of the volatility of the samples was carried out, revealing a slight increase in volatility following treatment with the B2O3 additive, with the exception of the MgF2–B2O3 system. A plausible mechanism elucidating the influence of B2O3 on oxygen-containing impurities present in metal fluorides is proposed.