  The A15 structure of superconductors is a prototypical type-II superconductor
that has generated considerable interest since the early history of
superconducting materials. This paper discusses the superconducting properties
of previously unreported V3-xCoxSi alloys. It is found that the lattice
parameter decreases with increasing cobalt-doped content and leads to an
increased residual resistivity ratio (RRR) value of the V3-xCoxSi system.
Meanwhile, the superconducting transition temperature (Tc) cobalt-doped
content. Furthermore, the fitted data show that the increase of cobalt-doped
content also reduces the lower/upper critical fields of the V3-xCoxSi system.
Type-II superconductivity is demonstrated on all V3-xCoxSi samples. With higher
Co-doped content, V3-xCoxSi alloys may have superconducting and structural
phase transitions at low-temperature regions. As the electron/atom (e/a) ratio
increases, the Tc variation trend of V3Si is as pronounced as in crystalline
alloys and monotonically follows the trend observed for amorphous
superconductors.
