Jean Guyader

Nitrides and oxynitrides: Preparation, crystal chemistry and properties

Abstract As compared to oxides, nitride-type compounds can have specific properties and applications. The outline of this review focuses on the crystal chemistry of nitrides and oxynitrides. Given the nitride-oxynitride association, this article mainly deals with compounds which are predominantly covalent in character and does not include compounds which are metallic in character and in which nitrogen can be considered as an interstitial element. The classification which is used thus highlights the two main coordination polyhedra: nitrided or oxynitrided tetrahedra or octahedra.

DRIFTS Chamber for in Situ and Simultaneous Study of Infrared and Electrical Response of Sensors

A diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) chamber suitable for in situ and simultaneous analysis of the infrared and electrical response of sensors is tested and described in detail. Experiments on a CdGeON sensor show some results about its reversible/ irreversible behavior in terms of temperature and under N2 atmosphere. A direct relationship between the conductivity and the elimination of DRIFTS peaks at 810,780, and 580 cm−1 is observed. From both DRIFTS spectra and conductivity measurements, an explanation involving the presence and filling of vacancies in the solid framework is proposed.

Detection of NH3 and H2S with thick film semiconductor sensors based on Cd2−xGeO4−x−3yN2y oxynitrides

Abstract Ammonia and hydrogen sulfide gas sensing properties of Cd0.98GeO1.16N1.21 semiconducting oxynitride have been investigated. Cd2−xGeO4−x−3yN2y oxynitride phases have been prepared by nitridation of an oxide precursor and present a tetrahedral structure derived from the wurtzite-type as described for ZnxGeOyNz oxynitride phases in a former study. Thick films based on Cd0.98GeO1.16N1.21 phase exhibit higher electrical conductance (in the order of 10−6 Ω−1 in air) than ZnxGeOyNz thick films (about 10−9 Ω−1 in air). The maximum sensitivity ΔG/G0 of the sensors towards 10 ppm of H2S is equal to 1000% at 200°C and to 350% at 300°C towards 90 ppm of NH3. Moreover, the detection of H2S pollutant can also occur in nitrogen atmosphere. These results are correlated with semiconductor conductivity model. The interaction mechanisms between H2S or NH3 and the thick film surface are also discussed.

Li-Si-Al-O-N and Li-Si-O-N oxynitride glasses study and characterization

The extent of oxynitride glass regions has been determined within Li-Si-Al-O-N and Li-Si-O-N systems. Physical properties such as density, hardness, elastic moduli and characteristic temperatures have been studied in terms of nitrogen content in the vitreous network. A comparison between the two systems studied enables the role of aluminium in these alumino-silicated glasses to be precisely determined.

Humidity effect on baseline conductance and H2S sensitivity of cadmium germanium oxynitride thick film gas sensors

Abstract Cadmium germanium oxynitrides are excellent sensing materials for the detection of H 2 S. The effect of humidity on both the baseline conductance and on the sensitivity to H 2 S of thick-film gas sensors was investigated. The devices were subjected to dry and moist (varying relative humidity (RH)) air. Results showed that, unlike most semiconductor gas detectors, the presence of moisture has no significant effect on conductivity nor on the sensitivity to H 2 S of cadmium germanium oxynitride sensors. Hypotheses on surface processes accounting for such insensitivity are given. It appears likely that the surface states involved in responses to changes in RH are different from those involved in the detection of other gases.

Alumina-γ-aluminum oxynitride composites from alumina nitrided by ammonia

Abstract By reaction between transition (γ) aluminas from boehmite and ammonia (T ≈ 1000–1100°C), up to 1%wt nitrogen can be fixed in the form of a γ-aluminum oxynitride layer on γ-Al 2 O 3 surface grains. This layer delays the polymorphic transformation of γ- into α-Al 2 O 3 . For higher nitrogen contents, aluminum nitride appears. An application can be the preparation of partially nitrided Al 2 O 3 powder in γ-AlON and /or AlN, that can lead to γ-AlON single phase or Al 2 O 3 -γ-AlON composites. Such composites, obtained by γ-Al 2 O 3 partially nitrided in AlON, present γ-AlON along grain boundaries; that microstructure is efficient in increasing the composite wear resistance.

Preparation and characterization of a new tetrahedral oxynitride phase Cd2−xGeO4−x−3yN2y

Abstract A new oxynitride phase, Cd2−xGeO4−x−3yN2y, with 0.9 ≤ x ≤ 1.5 and 0.3 ≤ y ≤ 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 ≤ a ≤ 5.75 A, 6.80 ≤ b ≤ 6.85 A, and c ≈ 5.39 A. Electrical properties have been investigated and reveal that CdXGeOYNZ-based thick films can be used as gas sensors.