The present invention discloses a water electrolysis catalyst suitable for a polymer electrolyte water electrolysis apparatus, and an anode electrode membrane using the catalyst. The water electrolysis catalyst of the present invention is a water electrolysis catalyst containing iridium oxide in a powder form. The iridium oxide powder contains an amorphous iridium oxide powder, and an average particle size of the powder is 0.01 m or more and 30 m or less. The water electrolysis catalyst containing the iridium oxide powder of the present invention contains amorphous iridium oxide, shows a specific property in TG-DTA, and exhibits an exothermic peak in a region of 300 C. to 450 C. in the TG-DTA.

A ruthenium oxide powder has a rutile type crystal structure, has Lc/La of 0.6913 or greater, where La is a lattice constant of an a-axis and Lc is a lattice constant of a c-axis as measured by X-ray diffraction, and has a crystallite size of 10 nm or greater and 30 nm or less.

Provided is a method of producing a metal nanoparticle-oxide support complex structure, in which metal nanoparticles uniform in size are evenly distributed on the surface of oxide supports. A gas sensor with improved gas sensing ability and durability may be provided by using the same.

A bismuth-substituted rare earth iron garnet single crystal suitable for Faraday rotators and optical isolators with reduced insertion loss due to suppressed valence fluctuation of Fe ions is provided. The bismuth-substituted rare earth iron garnet single crystal of the present invention is characterized by the composition formula (Gd.sub.aLn.sub.bBi.sub.cMg.sub.3(a+b+c))(Fe.sub.dGa.sub.eTi.sub.fPt.sub.5(d+e+f))O.sub.12. In the composition formula above, 0.02f0.05, 0.02{3(a+b+c)}0.08, and 0.01{3(a+b+c)}{f+5(d+e+f)}0.01. Ln is a rare earth element and may be selected from Eu, Dy, Gd, Ho, Tm, Yb, Lu, and Y.

The present disclosure relates to a novel ruthenium oxide, a method of preparing the same, and a catalyst for selective hydrogenation of an aromatic compound or an unsaturated compound including the ruthenium oxide.