X-ray Absorption Near Edge Structure (XANES) microscopy of phase separation in superconducting Mg1-xScxB2

We report micro-fluorescence (mu-XRF) and micro-XANES (mu-XANES) analysis on the phase-separated samples belonging to the superconducting section Mg(1-x)Sc(x)B(2)for x > 0.27, where we have found a phase separation into a Sc-poor and a Sc-rich region. These phase-separated samples exhibit a critical temperature higher than the pristine MgB2. We have explored the actual Se distribution along the sample with micro-fluorescence (mu-XRF), with a beam spot size below I pm, and we found Sc-poor textures of 100 mu m size embedded in a Sc-matrix. With mu-XANES we have studied the chemical state of the Sc in the Sc-poor region, responsible of high T-c, and found that Se does not enter the MgB2 lattice. These results suggest that enhanced T, could be due to the strain, which can be induced by the Sc impurities or by the Sc-rich matrix. (c) 2007 Elsevier B.V. All rights reserved.