A Simple Urea Approach to N-Doped α-Mo₂C with Enhanced Superconductivity

Chemical doping is a critical factor in the development of new superconductors or optimizing the superconducting transition temperature (T_\rm c) of the parent superconducting materials. Here, a new simple urea approach is developed to synthesize the N-doped \alpha-Mo_2C. Benefiting from the simple urea method, a broad superconducting dome is found in the Mo_2C_1-xN_x (0\leqslant x \leqslant 0.49) compositions. X-ray diffraction results show that the structure of \alpha-Mo_2C remains unchanged and there is a variation of lattice parameters with nitrogen doping. Resistivity, magnetic susceptibility, and heat capacity measurement results confirm that T_\rm c was strongly increased from 2.68 K (x=0) to 7.05 K (x=0.49). First-principles calculations and our analysis indicate that increasing nitrogen doping leads to a rise in the density of states at the Fermi level and doping-induced phonon softening, which enhances electron-phonon coupling. This results in an increase in T_\rm c and a sharp rise in the upper critical field. Our findings provide a promising strategy for fabricating transition metal carbonitrides and provide a material platform for further study of the superconductivity of transition metal carbides.