X-ray Absorption Near Edge Structure (XANES) microscopy of phase separation in superconducting Mg_1−xSc_xB₂

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• 作者：M. Filippi ; S. Agrestini ; L. Simonelli ; N.L. Saini ; A. Bianconi ; S. De Negri ; M. Giovannini ; A. Saccone
• 关键词：Diborides ; Phase separation ; XANES
• 刊名：Spectrochimica Acta Part B ; Atomic Spectroscopy
• 出版年：2007
• 期刊代码：101_05848547
• 类别：ch
• 出版时间：July 2007
• 卷：62
• 期：6-7
• 页码：717-719
• 文件大小：319 K

摘要

We report micro-fluorescence (μ-XRF) and micro-XANES (μ-XANES) analysis on the phase-separated samples belonging to the superconducting section Mg_1−xSc_xB₂ 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 Sc distribution along the sample with micro-fluorescence (μ-XRF), with a beam spot size below 1 μm, and we found Sc-poor textures of 100 μm size embedded in a Sc-matrix. With μ-XANES we have studied the chemical state of the Sc in the Sc-poor region, responsible of high T_c, and found that Sc does not enter the MgB₂ lattice. These results suggest that enhanced T_c could be due to the strain, which can be induced by the Sc impurities or by the Sc-rich matrix.