An amorphous silica titania composite oxide powder, which is excellent in fluidity and good transparency, is used in comparison with an existing silica titania composite oxide particle.A powder consisting of an amorphous silica titania composite oxide particle that is not treated with a surface treatment agent;The refractive index at a wavelength ofVolume reference cumulative 50% diameter 0.1 μ M μ MParticle size 5.0 μ The particle content of more than m is less thanThe powder was dried in the atmosphere at 1100.degree. C. for 12 hours.The dried powder is 25 ° C.Absorbs moisture in a relative humidity ofFrom mass y before hygroscopic moisture and after hygroscopic mass(Y-X) / X × An amorphous silica titania composite oxide powder having a water absorption coefficient of less thanIn preparing silica coated silica titania composite oxidesStrictly adjusting silica coating conditionsIt can be produced by firing at 900 ° C. or higher.
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