Abstract: In a pattern forming method for selectively forming an oxide layer on a substrate surface, the substrate surface is selectively coated with a coating layer. On the coating layer and an exposed part of the substrate surface, an oxide layer is formed by the use of a predetermined solution. Subsequently, the oxide layer on the coating layer is removed together with the coating layer to selectively leave the oxide layer on the substrate surface. Thus, a pattern is formed. The coating layer is removed in a liquid phase or optically together with the oxide layer on the coating layer. The oxide layer is formed by the use of, as the predetermined solution, an aqueous solution or a hydrofluoric acid solution of a fluoro metal complex compound and/or metal fluoride of at least one element selected from the group consisting of alkaline earth metal, transition metal, gallium, indium, silicon, tin, lead, antimony, and bismuth in the presence of an fluoride ion capturing agent.

Abstract: The present invention relates to a process for producing a titanium oxide thin film, said process comprises soaking a substrate in an aqueous solution containing 10.sup.-9 to 9.times.10.sup.-2 mol/L of a titanium fluoro complex compound in the presence of a fluoride ion capturing agent to form a titanium oxide thin film on the surface of the substrate; and a photocatalyst comprising the titanium oxide thin film thus produced; and can provide a simple process for the formation of a highly homogeneous titanium oxide thin film which is fast and corrosion resistant, and has a high refractive index and a catalytic activity for the photoreaction.

Abstract: This invention relates to a process for producing metal oxide precipitates, which comprises making a fluoride ion-capturing agent exist in an aqueous solution or hydrofluoric acid solution containing a fluorocomplex compound and/or a fluoride of a rare earth to form precipitates comprising a rare earth oxide or a solid solution containing it as a main component; and a process for producing metal oxide precipitates, which comprises making seed crystal(s) and a fluoride ion-capturing agent exist in an aqueous solution or hydrofluoric acid solution containing a metal fluoro complex compound and/or a metal fluoride of zirconium and/or hafnium to form precipitated crystals comprising said metal oxide crystals or a solid solution containing them as a main component, and is suitable for producing precipitates of a rare earth oxide and crystal precipitates of zirconium oxide and/or hafnium oxide, particularly precipitates such as a thin film, etc.

Abstract: This invention relates to a process for producing metal oxide precipitates, which comprises making a fluoride ion-capturing agent exist in a mixed solution of (1) an aqueous solution or hydrofluoric acid solution containing a fluoro complex compound and/or a metal fluoride each having a rare earth metal and/or an alkaline earth metal atom(s) M.sup.1 ; and (2) an aqueous solution or hydrofluoric acid solution containing a metal fluoro complex compound and/or a metal fluoride each having a transition metal and/or a 3B group metal atom(s) M.sup.2 to form precipitates comprising a perovskite type complex oxide containing M.sup.1 and M.sup.2, and is suitable for producing precipitates of a perovskite type complex oxide, particularly precipitates such as a thin film or the like on the surface of a substrate which has a large area or complicated shape, by using a simple apparatus without requirement of a heating step for crystallization.