研究目的
To explore the nitridation reactions of precursor oxides containing transition metal cations that can be easily reduced (e.g., Mo, V) under mild ammonolysis conditions to verify the extent of nitrogen incorporation.
研究成果
Fluorite oxynitrides M2MoTiO5-xN2+x-δ were successfully synthesized from scheelite precursors under mild ammonolysis, with Mo oxidation states reduced to 5.5-5.8 and nitrogen incorporation around 2-2.2 per formula unit, stabilized by anion vacancies. Zircon precursors yielded perovskite MVO3 oxides instead of oxynitrides, indicating limitations in nitrogen retention. The mild conditions offer a safer alternative to harsh reduction methods like hydrogen gas.
研究不足
The study was limited by the inability to confirm pyrochlore structure formation in some cases due to weak reflections in PXRD patterns. For Eu-based products, impurity phases (Eu2Ti2O7) interfered with analysis. The ammonolysis conditions (temperature, duration) may not fully optimize nitrogen incorporation, and some products like MVO3 perovskites showed minimal nitrogen content, possibly due to nitrogen loss during cooling.
1：Experimental Design and Method Selection:
The study involved ammonolysis reactions using nitrogen gas enriched with ammonia vapor at 800-850 °C to synthesize oxynitrides and perovskites from scheelite and zircon oxide precursors. Characterization methods included elemental analysis, TGA, PXRD, magnetic susceptibility, XPS, FTIR, and Raman spectroscopy.
2：Sample Selection and Data Sources:
Precursors were M2MoTiO8 (M = Eu, Gd, Dy, Y) and MVO4 (M = Ce, Sm, Gd, Dy) oxides, prepared from high-purity oxides (Aldrich, 99.9%) by solid-state reactions at specified temperatures.
3：9%) by solid-state reactions at specified temperatures.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment included PANalytical's Empyrean diffractometer for PXRD, Elementar Analysenysteme GmbH Vario EL III for elemental analysis, Perkin Elmer PyrisTM 1 TGA, Perkin Elmer 2000 FTIR spectrometer, VG Microtech Multilab ESCA 3000 XPS instrument, Quantum Design MPMS SQUID magnetometer. Materials included ammonia gas (Merck, 30%), high-purity oxides from Aldrich.
4：Experimental Procedures and Operational Workflow:
Precursors were synthesized by heating stoichiometric mixtures of oxides. Ammonolysis was performed at 800-850 °C for 6-12 h under nitrogen enriched with ammonia. Samples were cooled to room temperature under the same atmosphere. Characterization involved collecting PXRD patterns, elemental analysis for nitrogen content, TGA in oxygen, FTIR spectra, XPS measurements after surface cleaning, and magnetic susceptibility measurements.
5：Data Analysis Methods:
Le Bail refinements of PXRD data, XPS core-level spectra fitting with Gaussian distributions, calculation of magnetic moments from susceptibility data, and comparison with expected values based on oxidation states and nitrogen content.
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