Superconductivity with TcT_c up to 30.7 K in air-annealed CaFeAsF

Exploring new unconventional superconductors is of great value for both fundamental research and practical applications. It is a long-term challenge to develop and study more hole-doped superconductors in 1111 system of iron-based superconductors. However, fifteen years after the discovery of iron-based superconductors, it has become increasingly difficult to discover new members in this system by conventional means. Here we report the discovery of superconductivity with the critical transition temperature up to 30.7 K in the parent compound CaFeAsF by an annealing treatment in air atmosphere. The superconducting behaviors are verified in both the single-crystalline and polycrystalline samples by the resistance and magnetization measurements. The analysis by combining the depth-resolved time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) measurements show that the introduction of oxygen elements and the consequent changing in Fe valence by the annealing treatment may lead to the hole-type doping, which is the origin for the occurrence of superconductivity. Our results provide a new route to induce hole-doped superconductivity in Fe-based superconductors.Comment: 20 pages, 4 figures and 1 tabl

Strontium(II) Ion Surface-Imprinted Polymers Supported by Potassium Tetratitanate Whiskers: Synthesis, Characterization and Adsorption Behaviours

Novel surface strontium(II) ion-imprinted adsorbent particles have been prepared via the copolymerization of chitosan as the monomer, γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) as the cross-linking agent and 2,2′-azobisisobutyronitrile (AIBN) as the initiator in the presence of SrCl 2 • 6H 2 O. The prepared imprinted adsorbent was used for the selective solid-phase extraction (SPE) of trace Sr(II) ions in a practical sample prior to its determination by inductively coupled plasma–atomic emission spectrometry (ICP–AES). The results suggest that the adsorption kinetic data accorded better with the pseudo-second-order model, while the adsorption equilibrium data gave a good fit to the Langmuir isotherm equation, yielding a maximum adsorption capacity of 27.58 mg/g and a Langmuir adsorption equilibrium coefficient of 0.0363 ℓ/mg at 298 K. The relative selectivity coefficient values of Sr(II) ion-imprinted particles were several times greater than those for the non-imprinted matrix. The new Sr(II) ion-imprinted micro-beads were successfully applied for the separation of Sr(II) ions from river and clay samples. The detection limit (3σ) for Sr(II) ions as determined by flame atomic absorption spectrometry (FAAS) was 0.21 ng/mℓ. The relative standard deviation (RSD) for the determination of Sr(II) ions was 6–9% over the concentration range 0.03–0.3 mg/ℓ