High-Pressure Synthesis of Superconducting Molybdenum Nitride δ-MoN by in Situ Nitridation

Stoichiometric highly crystalline δ-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 ∼ 0.5, y ∼ 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 δ-MoN with superconductive transition temperature (Tc) 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.