New oxypnictide superconductors: PrOFe1−xCoxAs

Oxypnictides of the type PrOFe1−xCoxAs (x≤0.3) were synthesized for the first time by the sealed tube method. All the compounds were found to be monophasic and crystallize in the tetragonal ZrCuSiAs type structure (space group=P4/nmm) and the lattice parameters (a and c) decrease with increase in cobalt content. Mössbauer measurements of the compounds indicate low spin Fe2+ in tetrahedral coordination. Resistivity and magnetization studies reveal superconducting transitions in compounds with ‘x’=0.05, 0.10 and 0.15, with maximum transition temperature (Tc) at ∼14 K in the compound with ‘x’=0.1. The variation of resistivity with temperature under different magnetic field has been studied to estimate the upper critical field (Hc2) (∼50.2 T for the ‘x’=0.1 composition). The Seebeck and Hall coefficient (RH) suggests electron type charge carriers in these compound and the charge carrier density increases with increase in Co-doping.