Chemical state and properties of the Nb 5Sn 2Ga grown by the self-component flux method using tin as a solvent

Abstract

Single crystals of a new compound Nb 5Sn 2Ga were obtained by the flux method using molten tin as a solvent. The crystal structure represents a tetragonal symmetry, space group D 4h 18 I4/ mcm, ordered W 5Si 3-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 Nb 5Sn 2Ga. The compound shows superconductivity at T c =1.75 K and Δ T c =140 mK. The residual resistivity ratio, RRR= ρ (293 K)/ ρ (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 Nb 5Sn 2Ga starts at 562°C. Weight gain of the compound heated up to 1200°C in air is 37.3%. Final oxidation product contains NbO 2, Nb 2O 5, Nb 12O 29, SnO 2 and Ga 2O 3.