Chemical state and properties of the Nb₅Sn₂Ga grown by the self-component flux method using tin as a solvent

Single crystals of a new compound Nb₅Sn₂Ga were obtained by the flux method using molten tin as a solvent. The crystal structure represents a tetragonal symmetry, space group D¹⁸_4hI4/mcm, ordered W₅Si₃-type structure. Lattice parameters are a=1.0586(2) nm and c=0.5177(1) nm. According to XPS study, the peaks of Nb, Sn and Ga 3dXP spectra negatively shift when the three elements of Nb, Sn and Ga form the compound of Nb₅Sn₂Ga. The compound shows superconductivity at T_c=1.75 K and ΔT_c=140 mK. The residual resistivity ratio, RRR=ρ (293 K)/p (4.2 K), is 12. The Micro-Vickers hardness (MVH) value for the (100) or (110) face is 8.9-8.5 GPa, and for the (001) face is 10.1-9.1 GPa. Oxidation of the Nb₅Sn₂Ga starts at 562°C. Weight gain of the compound heated up to 1200°C in air is 37.3%. Final oxidation product contains NbO₂, Nb₂O₅, Nb₁₂O₂₉, SnO₂ and Ga₂O₃.