Influence of Rb, Cs and Ba on Superconductivity of Magnesium Diboride

Magnesium diboride has been thermally treated in the presence of Rb, Cs, and Ba. Magnetic susceptibility shows onsets of superconductivity in the resulting samples at 52K (Rb), 58K (Cs) and 45K (Ba). Room-temperature 11B NMR indicates to cubic symmetry of the electric field gradient at boron site for the samples reacted with Rb and Cs, in contrast to the axial symmetry in the initial MgB2 and in the sample treated with Ba.Comment: 3 pages (twocolumn), 2 figure

Diamond formation by thermal activation of graphite

Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces, microelectronics and optics to techniques to produce diamond as the thermodynamically stable form(3), but it can also be grown at low pressures as a metastable carbon phase(1,2). Here we report the production of high-purity cubic diamond microparticles (10-100 mu m), which form in a highly concentrated carbon-vapour phase, followed by deposition of the crystals on the substrate, The carbon-vapour phase is generated by thermal activation of graphite, and the fast initial growth-rates of diamond, in the range 100-500 mu m s(-1), are at least two orders of magnitude higher than previously reported(1,2). We expect that tuning of experimental parameters to optimize the density of the carbon-vapour phase will allow us to grow larger diamond crystals, thereby opening a wider range of potential practical applications