We have performed structural analyses on iron-based superconductors, PrFeAsO1-y and PrFeAsO1-xFx, systematically, by means of Rietveld method on neutron powder diffraction data. The shifts of iron ion valence from +2, δ, are accurately determined from the occupancies of O and O1-xFx sites obtained by the Rietveld analysis and F-concentration obtained by secondary ion-microprobe mass spectrometry. Tc-δ curve of PrFeAsO1-y is different from the curve of PrFeAsO1-xF x, indicating that δ is not a principal parameter for Tc in so-called 1111 system. Structural parameters of the FeAs layers, for example, As-Fe-As bond angle and As-height from Fe layer, are different between both systems with similar δ-values. Their parent compounds are also found to have different structural parameters, possibly due to the different synthetic conditions. These results suggest that the difference of structural parameters of FeAs layer is the origin of the discrepancy of Tc-δ curves of both systems and the Tc-value in the 1111 system is sensitive to the structural parameters. It may be attribute to an energy balance of the conducting bands contributing to the superconductivity.
All Science Journal Classification (ASJC) codes
- 物理與天文學 (全部)