This invention presents a new class of multicomponent metallic oxides which are particularly suited toward use in fabricating components used in processes for producing syngas. The non-stoichiometric, A-site rich compositions of the present invention are represented by the formula (LnxCa1−x)y FeO3−&dgr;wherein Ln is La or a mixture of lanthanides comprising La, and wherein 1.0>x>0.5, 1.1≧y>1.0 and &dgr; is a number which renders the composition of matter charge neutral. Solid-state membranes formed from these compositions provide a favorable balance of oxygen permeance and resistance to degradation when employed in processes for producing syngas. This invention also presents a process for making syngas which utilizes such membranes.