We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (T c) exhibits a trapezoid shape dependence on the F- content, with the highest T c of ∼26 K at ∼11 atom %.

A layered oxyphosphide, LaNiOP, was synthesized by solid-state reactions. This crystal was confirmed to have a layered structure composed of an alternating stack of (La(3+)O(2-))(+) and (Ni(2+)P(3-))(-). We found that the resulting LaNiOP shows a superconducting transition at approximately 3 K. This material exhibited metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. The resistivity sharply dropped to zero and the magnetic susceptibility became negative at <4 K, indicating that a superconducting transition occurs. The volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reached approximately 40 vol % at 1.8 K, substantiating that LaNiOP is a bulk superconductor.

Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with T c = 26 K. -Electrical conductivity and magnetization measurements demonstrate that the Fion-doped layered compound LaOFeAs is a bulk superconductor. The transition temperature changes with Fcontent, exhibiting a maximum transition temperature of about 26 K at a Fcontent of approximately 11 at.%. The magnetic susceptibility indicates that F-doped LaOFeAs exhibits Curie-Weiss-like behavior in the normal conducting state. -(KAMIHARA*, Y.; WATANABE, T.; HIRANO, M.; HOSONO, H.; J. Am. Chem. Soc. 130 (2008) 11, 3296-3297; ERATO-SORST, Front. Res. Cent., Japan Sci. Technol. Agency, Midori, Yokohama 226, Japan; Eng.) -W. Pewestorf 25-008

The first-, second-, and third-generation dendrimer-like branched poly(methyl methacrylate)s (PMMA)s were synthesized by an iterative divergent approach which involves a coupling reaction of α-functionalized living anionic PMMA with chain-end-functionalized PMMA with benzyl bromide moieties and a transformation reaction of the tert-butyldimethylsilyloxymethylpheny groups into benzyl bromide functionalities. The iterative reaction sequence could be repeated three times without problem to afford a series of three generations dendrimer-like branched PMMAs with well-defined architectures and precisely controlled chain lengths. Moreover, an amphiphilic dendrimer-like branched block copolymer was synthesized successfully in a similar manner by using the living anionic polymer of the protected 2-hydroxyethyl methacrylate (HEMA) instead of living anionic PMMA at the final reaction stage. The resulting polymer was made of the inner 1, 4, and 8 PMMA segments and the outer 16 poly(HEMA) segments. The solution behaviors were followed by 1H NMR spectra. The formation of micelles was strongly indicated in both CDCl3/CD3OD (98/2, v/v) and CDCl3/CD3OD (5/95, v/v) mixtures.

Rietveld analysis of the powder X-ray diffraction of a new layered oxyarsenide, LaNiOAs, which was synthesized by solid-state reactions, revealed that LaNiOAs belongs to the tetragonal ZrCuSiAs-type structure (P4/nmm) and is composed of alternating stacks of La-O and Ni-As layers. The electrical and magnetic measurements demonstrated that LaNiOAs exhibits a superconducting transition at 2.4 K, and above this, LaNiOAs shows metallic conduction and Pauli paramagnetism. The diamagnetic susceptibility measured at 1.8 K corresponded to ~20% of perfect diamagnetic susceptibility, substantiating that LaNiOAs is a bulk superconductor.