Comparison of crystal structures and effects of Co substitution in a new member of Fe-1111 superconductor family AeFeAsF(Ae = Ca and Sr): a possible candidate for higher Tc superconductor

Abstract

We refined crystal structures of newly found members of the Fe-1111 superconductor family, CaFe\_{1-x}Co\_{x}AsF and SrFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) by powder synchrotron X-ray diffraction analysis. The tetragonal to orthorhombic phase transitions were observed at ~120 K for unsubstituted CaFeAsF and at ~180 K for unsubstituted SrFeAsF, the transition temperatures agreeing with kinks observed in temperature-dependent resistivity curves. Although the transition temperature decreases, the structural phase transitions were observed below 100 K in both samples of x = 0.06, and finally they were suppressed in the doping level of x = 0.12. The refined structures reveal that distortions of the FeAs4 tetrahedron from the regular tetrahedron likely originate from mismatches in atomic radii among the constituent elements. In this system, the enlarged FeAs4 tetrahedron resulting from larger radius of Sr than that of Ca is flattened along a-b plane, whereas the smaller radius of Ca makes the tetrahedron closer to regular one, and their characteristic shapes are further enhanced by Co substitution. These results suggest that the CaFeAsF compound is a promising candidate for higher-Tc superconductor.

17 pages, 8 figures, 2 tables, Supplementary information is included at the end of the document

References in corpus (17)

• Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems
• Superconductivity at 43 K in Samarium-arsenide Oxides $SmFeAs{O}_{1-x}{F}_x$
• Superconductivity at 22 K in Co-doped BaFe2As2 Crystals
• The superconductivity at 18 K in LiFeAs system
• Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln=La,Nd)
• Superconductivity in Co-doped LaFeAsO
• Evolution from Itinerant Antiferromagnet to Unconventional Superconductor with Fluorine Doping in La(O_{1-x}F_{x})FeAs Revealed by ^{75}As and ^{139}La Nuclear Magnetic Resonance
• Crystallographic Phase Transition and High-Tc Superconductivity in LaFeAsO:F
• Superconductivity induced by cobalt doping in iron-based oxyarsenides
• Effect of Co doping on superconductivity and transport properties in SmFe${}_{1-x}$Co${}_x$AsO
• Crystal structure and phase transitions across the metal-superconductor boundary in the SmFeAsO1-xFx (0 < x < 0.20) family
• Nickel-based layered superconductor, LaNiOAs
• Magnetic Ordering and Negative Thermal Expansion in PrFeAsO
• Spin Ordering in LaOFeAs and Its Suppression in Superconductor LaO0.89F0.11FeAs Probed by Mössbauer Spectroscopy
• Synthesis, crystal structure and spin-density-wave anomaly of the iron arsenide-fluoride SrFeAsF
• Cobalt-substitution-induced Superconductivity in a New Compound with ZrCuSiAs-type Structure, SrFeAsF
• Superconductivity in Co-doped SmFeAsO

Cited by in corpus (5)

• New iron-based arsenide oxides (Fe2As2)(Sr4M2O6)(M = Sc, Cr)
• Tight binding model for iron pnictides
• Homogeneous coexistence of SDW and SC states in CaFe(1-x)Co(x)AsF studied by nuclear magnetic resonance
• Spin density wave and superconductivity in CaFe_{1-x}Co_{x}AsF studied by nuclear magnetic resonance
• Apparatus Design for Measuring of the Strain Dependence of the Seebeck Coefficient of Single Crystals