Polycrystalline Ca and F co-doped LaFeAsO samples (La 1-x Ca x FeAsO 1-y F y ) were synthesized by solid-state reactions. Samples with nominal composition: (y - x) ≤ 0.05 did not show superconductivity at temperatures T > 4.2 K, although an anomalous kink of the ρ-T curves, which is related to crystallographic phase transitions, was observed at T ∼ 150 K. Samples with nominal composition: (y - x) ≥ 0.15 did exhibit superconductivity. The superconducting transition temperature (T c ) of co-doped LaFeAsO with nominal composition: (x, y) = (0.25, 0.50) was determined to be T c = 31.5 K, which is higher than the highest T c value observed for LaFeAsO 1-x F x materials synthesized under ambient pressure.
ASJC Scopus subject areas
- Physics and Astronomy(all)