Abstract: The present invention presents a fluid separation device capable of separating oxygen from an oxygen-containing gaseous mixture which utilizes at least one solid-state membrane comprising a dense mixed conducting multicomponent metallic oxide layer formed from a mixed conducting multicomponent metallic oxide represented by the formulaLn.sub.x A'.sub.x A".sub.x B.sub.y B'.sub.y O.sub.3-z,wherein Ln is an element selected from the f block lanthanides, A' is selected from Group 2, A" is selected from Groups 1, 2 and 3 and the f block lanthanides, and B,B' are independently selected from the d block transition metals, excluding titanium and chromium, wherein 0.ltoreq.x<1, 0<x'.ltoreq.1, 0.ltoreq.x"<1, 0<y<1.1, 0.ltoreq.y'<1.1,x+x'+x"=1.0, 1.1>y+y'>1.0 and z is a number which renders the compound charge neutral.

Abstract: The present invention presents a new class of multicomponent metallic oxides which are particularly suited toward use in fabricating components used in solid-state oxygen separation devices. The compositions of the present invention are represented by the formula Ln.sub.x A'.sub.x' A".sub.x" B.sub.y B'.sub.y' B".sub.y" O.sub.3-z, wherein Ln is an element selected from the f block lanthanides, A' is selected from Group 2, A" is selected from Groups 1, 2 and 3 and the f block lanthanides, and B,B',B" are independently selected from the d block transition metals, excluding titanium and chromium, wherein 0.ltoreq.x<1, 0<x'<1, 0.ltoreq.x"<1, 0<y<1.1, 0<y'<1.1, 0<y"<1.1, x+x'+x"=1.0, 1.1>y+y'+y">1.0 and z is a number which renders the compound charge neutral wherein such elements are represented according to the Periodic Table of the Elements adopted by IUPAC.