High pressure synthesis of superconducting nitrides in the MoN-NbN system.
J MATER CHEM
4176 - 4182.
We have synthesized a range of Mo-Nb nitrides at 2.5 GPa and T = 1600 degrees C or 2200 degrees C using high pressure-high temperature techniques. Following syntheses at 1600 degrees C Mo-rich compositions are hexagonal and Nb-rich phases are cubic, with a narrow two-phase region indicating the presence of a solvus. The maximum Mo content in the cubic phase derived from delta-NbN is 40-44 mol%, and the maximum Nb content in the hexagonal delta-MoN phase is 46-47 mol%. There was little variation in the superconducting transition temperature T-c for hexagonal delta-(Mo, Nb) N samples produced in the study. Previous studies showed maximum T-c values of 12-15 K for pure delta-MoN as a function of N-site ordering in high-P, T experiments. Here we recorded T-c 14 K for the limiting Mo-rich composition prepared in the study. We observed T-c = 11.5-16 K for cubic delta-NbN depending on high-P, T synthesis and annealing conditions. This value falls to 5 K for the cubic Mo0.37Nb0.63N0.98 solid solution phase. Some high-P, T synthesis or annealing experiments were carried out at T 2200 degrees C. At this temperature delta-MoN decomposes to produce gamma-MoN0.54. A minor phase in this sample achieves T-c = 9.5 K. A new superconducting hexagonal oxynitride MoN0.74O0.38 with T-c = 16 K was also produced during this study.
|Title:||High pressure synthesis of superconducting nitrides in the MoN-NbN system|
|Keywords:||CRYSTAL-STRUCTURE, DELTA-MON, HIGH-TEMPERATURE, RAMAN-SPECTRA, GAMMA-MO2N, DIFFRACTION, TRANSITION, PHONON, TC|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry|
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