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 Mo 2 N powder (layer 1) and a mixture of Mo 2 N 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, Mo 2 N reacts with Ni metal in layer 2 to form less nitrogen-containing phase MoNi x N y ( x ∼ 0.5, y ∼ 0.2) and nitrogen, where the nitrogen moved into layer 1 and reacted with Mo 2 N. X-ray diffraction, electron microprobe analysis, and magnetic measurements demonstrated the formation of stoichiometric δ-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.