Search

We report that the incorporation of hydroxide ions (OH)- significantly enhances the superconducting transition temperature (Tc) in the LnFeAsO-based superconductors (Ln1111: Ln=La, Ce, and Pr). For La1111, Tc of the (OH)- incorporated sample synthesized using high-pressure technique becomes 35 K, which is higher by 7 K than the typical optimally doped La1111 superconductors. Similar enhancement in Tc is also observed for Ce1111 and Pr1111. 1H-NMR measurement have confirmed the existence of hydrogen atoms in the samples. Accompanying the (OH)- incorporation, the lattice parameters are largely contracted, down to the values which have never been attained by any other dopings/substitutions. [ABSTRACT FROM AUTHOR]

We report synthesis and properties of the simplest double-layered cuprate superconductor Ba2CaCu2O4(O,F)2. A superconducting transition temperature (Tc) has been achieved as high as 108 K for a sample with a nominal fluorine content y=1.6 in Ba2CaCu2O6-yFy. The Tc is the highest among double-layer cuprates that are free of toxic elements such as Hg, Tl, and Pb so that the nontoxic Ba2CaCu2O4(O,F)2 will be promising for application. As y decreases from approximately 2, the a-axis length decreases and the Tc increases from 40 to 108 K. The material is underdoped at large y and as y decreases, the doping moves toward an optimally doped state. [ABSTRACT FROM AUTHOR]

High-density bulk materials of a recently discovered 40 K intermetallic MgB[sub 2] superconductor were prepared by high-pressure sintering. Superconducting transition with the onset temperature of 39 K was confirmed by both magnetic and resistive measurements. Magnetization versus field (M-H) curve shows the behavior of a typical type-II superconductor and the lower critical field H[sub c1](0) estimated from the M-H curve is 0.032 T. The bulk sample shows good connection between grains and critical current density J[sub c] estimated from the magnetization hysteresis using sample size was 5x10[sup 4] A/cm[sup 2] at 20 K and 1 T. Upper critical field H[sub c2](0) determined by extrapolating the onset of resistive transition and assuming a dirty limit is 18 T. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]