A satisfactory oxygen storage material and a method for producing it are provided. The oxygen storage material comprises zirconia particles with a ceria-zirconia complex oxide supported on the zirconia particles. The ceria-zirconia complex oxide includes a pyrochlore phase and has a mean crystallite diameter of 10 nm to 22.9 nm.

Provided is a cerium-zirconium-based composite oxide having an excellent OSC, high catalytic activity, and excellent heat resistance, and also provided is a method for producing the same. The cerium-zirconium-based composite oxide comprises cerium, zirconium, and a third element other than these elements. The third element is (a) a transition metal element or (b) at least one or more elements selected from the group consisting of rare earth elements and alkaline earth metal elements. After a heat treatment at 1,000 C. to 1,100 C. for 3 hours, (1) the composite oxide has a crystal structure containing a pyrochlore phase, (2) a value of {I111/(I111+I222)}100 is 1 or more, and (3) the composite oxide has an oxygen storage capacity at 600 C. of 0.05 mmol/g or more, and an oxygen storage capacity at 750 C. of 0.3 mmol/g or more.

A template-free reverse micelle (RM) based method is used to synthesize pyrochlore nanostructures having photocatalytic activity. In one embodiment, the method includes separately mixing together a first acid stabilized aqueous solution including pyrochlore precursor A and a second acid stabilized aqueous solution including pyrochlore precursor B with an organic solution including a surfactant to form an oil-in-water emulsion. Next, equimolar solutions of the first and second acid stabilized oil-in-water emulsions are mixed together. Then, the mixture of the first and second acid stabilized oil-in-water emulsion is treated with a base to produce a precipitate including pyrochlore precursors A and B. After which, the precipitate is dried to remove volatiles. The precipitate is then calcined in the presence of oxygen to form a pyrochlore nanostructure, such as a bismuth titanate (Bi.sub.2Ti.sub.2O.sub.7) pyrochlore nanorod. The method of synthesizing the pyrochlore nanorod is template-free.

Provided are a composite oxide powder from which dense solid electrolyte objects having a high ion conductivity can be produced and a method for producing the composite oxide powder. The composite oxide powder is composed of particles comprising lithium (Li), lanthanum (La), zirconium (Zr), and oxygen (O) and having a cubic garnet-type crystal structure, and has a volume particle size distribution in which the 50% diameter (D50) is 1,000 nm or smaller, the composite oxide powder having a pyrochlore phase content of 10 mass % or less.

The present disclosure provides an oxygen storage/release material that has achieved both the improved oxygen storage/release capacity at low temperature and heat tolerance, which comprises a ceria-zirconia-based composite oxide, wherein the ceria-zirconia-based composite oxide further comprises praseodymium (Pr) or neodymium (Nd), and has, in at least a part thereof, at least one ordered phase of phase and a pyrochlore phase, a proportion of primary particles having particle diameters of 0.4 m to 1.5 m is 40% to 100% on a particle number basis, and, when heated for 5 hours in the air at 1,100 C., I(14/29) value is 0.015 or more and I(28/29) value is 0.08 or less. The present disclosure also relates to a method for producing such oxygen storage/release material.