A complex oxide powder contains cerium, zirconium, and aluminum and, has a specific surface area of 0.5 m.sup.2/g or more and 10 m.sup.2/g or less.

A lithium ion conductive solid electrolyte contains a lithium ion conductive powder having a garnet-type crystal structure including at least Li, La, Zr, and O, and a lithium ion conductive polymer. The lithium ion conductive solid electrolyte can maintain its shape without use of an additional polymer different from the lithium ion conductive polymer. The lithium ion conductive solid electrolyte exhibits an activation energy of 30 kJ/mol or less at 20° C. to 80° C.

A zirconia powder in which when a stabilizer is Y.sub.2O.sub.3, a content thereof is 1.4 mol % or more and less than 2.0 mol %; when the stabilizer is Er.sub.2O.sub.3, a content thereof is 1.4 mol % or more and 1.8 mol % or less; when the stabilizer is Yb.sub.2O.sub.3, a content thereof is 1.4 mol % or more and 1.8 mol % or less; and when the stabilizer is CaO, a content thereof is 3.5 mol % or more and 4.5 mol % or less; and in a range of 10 nm or more and 200 nm or less in a pore distribution, a peak top diameter of a pore volume distribution is 20 nm or more and 120 nm or less, a pore volume is 0.2 ml/g or more and less than 0.5 ml/g, and a pore distribution width is 30 nm or more and 170 nm or less.

A zirconia powder containing a stabilizer, and having a specific surface area of 20 m.sup.2/g or more and 60 m.sup.2/g or less and a particle diameter D.sub.50 of 0.1 μm or more and 0.7 μm or less, in which in a range of 10 nm or more and 200 nm or less in a pore distribution based on a mercury intrusion method, a peak top diameter in a pore volume distribution is 20 nm or more and 85 nm or less, a pore volume is 0.2 ml/g or more and less than 0.5 ml/g, and a pore distribution width is 40 nm or more and 105 nm or less.

A membrane electrode assembly of an electrochemical device includes a proton conductive solid electrolyte membrane and an electrode including Ni and an electrolyte material which contains as a primary component, at least one of a first compound having a composition represented by BaZr.sub.1-x1M.sup.1.sub.x1O.sub.3 (M.sup.1 represents at least one element selected from trivalent elements each having an ion radius of more than 0.720 A° to less than 0.880 A°, and 0<x.sub.1<1 holds) and a second compound having a composition represented by BaZr.sub.1-x2Tm.sub.x2O.sub.3 (0<x.sub.2<0.3 holds).

A solid electrolyte which contains a garnet-type composite metal oxide phase (L) and shows an excellent lithium ion conductivity is provided. The solid electrolyte contains a garnet-type composite metal oxide phase (L) and a phase (D) different from the phase (L). The phase (L) contains Li, La, Zr, O, and Ga, and an Li site in the phase (L) is substituted with the Ga. A lattice constant of the solid electrolyte is not smaller than 12.96 Å. The phase (D) contains at least one of LiF, BaZrO.sub.3, YF.sub.3, SrF.sub.2, and ScF.sub.3.

Disclosed is a method of decontamination by exposing a zirconium oxy(hydroxide) aerogel to a liquid, vapor, or gaseous sample suspected of containing a phosphonate compound. The aerogel may be doped with Fe.sup.3+ ions, Ce.sup.3+ ions, or SO.sub.4.sup.2− ions. The aerogel may be made by: providing a solution of ZrCl.sub.4; FeCl.sub.3, CeCl.sub.3, or Zr(SO.sub.4).sub.2; and a solvent; adding a cyclic ether to the solution to form a gel; infiltrating the gel with liquid carbon dioxide; applying a temperature and pressure to form supercritical fluid carbon dioxide; and removing the carbon dioxide for form an aerogel.

Disclosed is a method of decontamination by exposing a zirconium oxy(hydroxide) aerogel to a liquid, vapor, or gaseous sample suspected of containing a phosphonate compound. The aerogel may be doped with Fe.sup.3+ ions, Ce.sup.3+ ions, or SO.sub.4.sup.2− ions. The aerogel may be made by: providing a solution of ZrCl.sub.4; FeCl.sub.3, CeCl.sub.3, or Zr(SO.sub.4).sub.2; and a solvent; adding a cyclic ether to the solution to form a gel; infiltrating the gel with liquid carbon dioxide; applying a temperature and pressure to form supercritical fluid carbon dioxide; and removing the carbon dioxide for form an aerogel.

An object of the present invention is to provide means for releasing oxygen at a temperature lower than conventional means in an exhaust gas purification catalyst. A Ce—Zr composite oxide is provided, which has a crystallite diameter of 6.5 nm or less and a BET specific surface area of 90 m.sup.2/g or more.

An object of the present invention is to provide means for releasing oxygen at a temperature lower than conventional means in an exhaust gas purification catalyst. A Ce—Zr composite oxide is provided, which has a crystallite diameter of 6.5 nm or less and a BET specific surface area of 90 m.sup.2/g or more.