New oxypnictide superconductors

Recently a new class of superconductors have been discovered based on the LnOFeAs (Ln = rare earth) structure. Our studies revolve around the substitution of ions at the rare earth, oxygen, iron and arsenic site in LnOFeAs. Here we describe our studies leading to several new families of oxypnictides which include a new methodology of synthesizing these oxypnictide superconductors with potassium fluoride (KF) and sodium fluoride (NaF) as a source of fluorine instead of LaF3 which leads to enhancement in Tc and high critical fields. Novel compositions have been designed to achieve high Tc and critical field (Hc2). We have obtained the first antimony-doped superconductor (which also enhances Tc to 30.1 K from 28.5 K). Novel compositions have been designed where the interplay of simultaneous electron and hole doping is observed. Enhancement in Tc, Hc2 and critical current (Jc) has been induced by increasing chemical pressure in Y-doped Ce/Y(O/F)FeAs. Superconductivity has also been induced by substitution of isovalent P-substitution in PrOFeAs