Quantitative XANES Spectroscopy Study on the Prototype Hole-and Electron-Doped High-T_c Superconductor Systems,(La,Sr)2CuO4 and(Nd,Ce)2CuO4

摘要

Here we demonstrate that the Cu L-edge XANES(X-ray absorption near-edge structure) spectroscopy can be employed for quantitative analysis of the level of carrier-doping in the prototype hole-and electron-doped high-T_c superconductor systems,(La_(1-x)Sr_x)2CuO_(4+delta) and(Nd_(1-x)Ce_x)2CuO_(4+delta).The progress in hole-doping in the(La_(1-x)Sr_x)2CuO_(4+delta) system is seen as development of the shoulder peak(due to nominally trivalent copper) on the high-energy side of the main peak(due to nominally divalent copper) in the Cu L3-edge region,whereas the progress in electron-doping in the(Nd_(1-x)Ce_x)2CuO_(4+delta) system results in an additional absorption peak at about 934 eV(due to nominally monovalent copper),together with a decrease in the intensity of the main peak(due to nominally divalent copper).On the basis of these features,Cu-valence values are quantitatively obtained in excellent agreement with those calculated for the same samples from the precise oxygen contents,4+delta,determined by means of wet-chemical analysis.The valence of Ce in(Nd_(1-x)Ce_x)2CuO_(4+delta) is revealed to be somewhat lower than +4(ca.+3.8) on the basis of Ce M5-edge XANES data.In the O K-edge XANES spectra,the increase in the CuO2-plane hole concentration with increasing x in(La_(1-x)Sr_x)2CuO_(4+delta) is seen as an enhancement in the intensity of the pre-edge feature at ~528.9 eV,whereas for(Nd_(1-x)Ce_x)2CuO_(4+delta),no signs are observed that could be directly assigned to the change in electron-doping level.