Tantalum pentoxide is a commonly used material with high refractive index, with a molecular weight of 441.89, a melting point of 1800°C, and an evaporation temperature of 1920°C under 10-2Pa vacuum. The emission of impurities is small. It can be evaporated by heating with tantalum, tungsten boats, and coils. The tungsten crucible is heated and evaporated, and the electron beam heating and evaporation effect is good.
Tantalum pentoxide has stable chemical properties. It is soluble in molten potassium hydrogen sulfate and hydrofluoric acid, but is insoluble in water or other acids. According to X-ray diffraction analysis, the raw material of tantalum pentoxide is orthorhombic crystal system, which is sintered at high temperature. The coating material is converted to a mixed crystal of triclinic system and tetragonal system.
The tantalum pentoxide film is stable and not easy to crystallize. Its transparent area is 0.3~10μm, the refractive index is n=2.25 (λ=0.4μm), n=2.1 (λ=0.55μm, Ts=250℃). It is transparent in the visible to infrared band. No matter it is plated by electron gun evaporation, magnetron sputtering or ion beam sputtering, it is more stable than plated titanium dioxide.According to the experience of electron gun plus ion-assisted coating and sputtering coating (Ta target), tantalum pentoxide is easier to obtain thin film with smaller absorption and scattering than titanium dioxide, and the deposition rate of the film can be faster, and the packing density is close to 1, So it is often used in combination with silicon dioxide to plate low-scattering, low-absorption multilayer filters, etc. It can also be used as a protective coating, especially in high-temperature environments.
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