Superconductivity in quaternary niobium oxynitrides containing main group elements (M=Mg, Al, Si)

Niobium compounds continue to be an interesting family of superconductors, with the recent addition of oxynitrides to it, which can be categorized as low-Tc superconductors (LTS) because they exhibit superconductivity below Tc∼17 K. In this paper, we report the superconducting properties of three members of the family of niobium oxynitrides, viz. (Nb0.89Al0.11)(N0.84O0.16), (Nb0.95Mg0.05)(N0.92O0.08) and (Nb0.87Si0.09□0.04)(N0.87O0.13). Low temperature dc and ac magnetization measurements have been performed. In addition, heat capacity has been recorded at low temperature under applied magnetic fields. A detailed analysis of the data is presented.