Synthesis and rapid sintering of dense SrA(O,N)3 (A = Mo, W) oxynitride ceramics

SrMo(O,N)3 and SrW(O,N)3 oxynitride powders were synthesized via a solvothermal route followed by ammonolysis. Their rapid densification by spark plasma sintering with a heating rate of 300–400 °C/min under a uniaxial pressure of 100 MPa yielded dense monoliths. The lowest open porosity achieved was 0 vol% for SrMo(O,N)3 and 7.6 vol% for SrW(O,N)3. The compacted monoliths were characterized by elemental analysis, electron microscopy (SEM, TEM) coupled with energy dispersive X-ray spectroscopy (EDX), as well as X-ray diffraction (XRD). Rietveld refinement of the XRD patterns revealed in the case of the compacted SrMo(O,N)3 the formation of small amount of ternary oxides (Sr3Mo2O7/SrMoO4/Sr3MoO6), molybdenum nitride (Mo2N), as well as metallic Mo. On the contrary, SrW(O,N)3 exhibited significant decomposition after consolidation, with SrWO4/Sr3WO6 being main components beside SrMo(O,N)3, accompanied by tungsten nitride (WN) and metallic W. Thus, rapid SPS enables the densification of oxynitrides with high density and acceptable purity that were hardly achieved earlier.