Ternary, pyrogenically prepared, crystalline metal mixed oxide powder having the components titanium and silicon and a third component chosen from the group comprising aluminium, zirconium, zinc, tin, magnesium, yttrium, vanadium, tungsten, tantalum, cerium or boron. It is prepared by a procedure in which a vaporizable or atomizable silicon and titanium compound and a vaporizable or atomizable compound of a third mixed oxide component are mixed with hydrogen and primary air and the gas mixture is burned into a reaction chamber, and the powder formed is separated off from the gaseous reaction products. It can be employed in sunscreen formulations.