High-pressure synthesis of superconducting molybdenum nitride δ-MoN by in situ nitridation

Stoichiometric highly crystalline delta-MoN was obtained by in situ nitridation reaction under high pressure of 10 GPa. We developed a nitrogen source usable for in situ nitridation reaction. The high-pressure cell used in this study was composed Of Mo2N powder (layer 1) and a mixture Of Mo2N and metallic Ni powders (layer 2, the nitrogen source), where a gas-permeable separator (a thin layer of boron nitride powder) was placed between the layers. At high temperature of 1300 K, Mo2N reacts with Ni metal in layer 2 to form less nitrogen-containing phase MoNixNy (x similar to 0.5, y similar to 0.2) and nitrogen, where the nitrogen moved into layer 1 and reacted with Mo2N. X-ray diffraction, electron microprobe analysis, and magnetic measurements demonstrated the formation of stoichiometric delta-MoN with superconductive transition temperature (T-c) as high as 14 K. This in situ nitridation method using the novel nitrogen source is versatile for preparation of other nitrides under high pressure.