Niobium nitride (NbNX) coatings were prepared onto Nb substrate by thermal diffusion at high temperatures. The formation of NbNX coating by thermal diffusion was studied in the range of 1250-1500 degrees C at constant nitrogen background gas pressure (1.3 x 10(-3) Pa) and processing time (180 min). The electronic and crystal structures of the NbNX coatings were investigated. It was found that nitrogen diffuses into Nb forming the Nb-N solid solution (bcc) alpha-NbN phase that starts to appear above 1250 degrees C. Increasing the processing temperature gives richer alpha-phase concentration. Besides, X-ray absorption spectroscopy (XAS) was performed to study the electronic structure of the NbNX layer. The results of the electronic structural study corroborate the crystal structural analysis. The Nb M-3,M-2 edge X-ray absorption spectroscopy (XAS) spectrum shows strong temperature dependence. At the highest processing temperature (1500 degrees C), the number of d holes increased. Electrostatic interaction between d electron and core hole was increased due to nitrogen diffusion into the niobium. For the studied conditions, only the alpha-NbN was observed in the X-ray diffraction patterns. (C) 2016 Elsevier B.V. All rights reserved.