PREPARATION AND CHARACTERIZATION OF A NEW TETRAHEDRAL OXYNITRIDE PHASE CD2-XGEO4-X-3YN2Y

A new oxynitride phase, Cd2-xGeO4-x-3yN2y, with 0.9 less than or equal to x less than or equal to 1.5 and 0.3 less than or equal to y less than or equal to 0.7 has been prepared by reaction of gaseous ammonia on a ''Cd-Ge-O'' amorphous phase. Its composition depends on the synthesis conditions and more particularly on the starting ratio Cd/Ge. The amorphous precursor is obtained by coprecipitation of cadmium and germanium oxides and gives after heating in air the crystallized double oxide Cd2GeO4 with or without the CdO oxide phase, depending on the initial Cd/Ge ratio. The oxynitrides obtained after nitridation have been characterized by chemical analysis and X-ray diffraction. They present a tetrahedral structure derived from the wurtzite type with orthorhombic symmetry, The lattice parameters are 5.60 less than or equal to a less than or equal to 5.75 Angstrom, 6.80 less than or equal to b less than or equal to 6.85 Angstrom, and c approximate to 5.39 Angstrom. Electrical properties have been investigated and reveal that CdXGeOYNZ-based thick films can be used as gas sensors. (C) 1995 Academic Press, Inc.