Process for preparing a composite electrolyte based on BIMEVOX and the use of said compound in separating oxygen from a gas mixture

A process for preparing a solid composite electrolyte comprising at least one compound of the BIMEVOX family, which process comprises:

• a) at least one step of preparing a mixture of one or more compounds of the BIMEVOX family with one or more chemically inert compounds, selected from the group consisting of carbides, nitrides and oxides;
• b) at least one step of compacting the mixture obtained from step a);
• and
• c) at least one sintering step during which the temperature reached, over a nonzero time interval, has a value greater than the optimum sintering temperature for said compound of the BIMEVOX family;
• wherein said one or more compounds of the BIMEVOX family is an oxide derived from Bi4V2O11.