Low temperature synthesis, crystal structure and thermal stability studies of nanocrystalline VN particles

摘要

The simultaneous thermal decomposition and nitridation of [VO(NH_2O)_2Gly]·H_2O complex in NH_3 atmosphere at 723-973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8-32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26-100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm~(-1) which gives the force constant of 634.3 Nm~(-1). The electrical resistivity and magnetic studies show the superconducting to normal transition (T_c) at 9.2 K. Thermal decomposition of VN is carried out in O_2 atmosphere which goes through the formation of an oxynitride (V-N_p-O_q) intermediate phase up to 913 K. Finally, nanocrystalline V_2O_5 is formed at 973 K. The V_2O_5 has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 A and the XRD crystallite size of 10 nm.