Soft X-ray spectra by wavelength dispersive spectrometry as a micron scale tool to determine copper valence

Copper in liquids in many cuprate systems occurs in both univalent and divalent states. The determination of Cu valence in experimental charges is necessary for full understanding of phase relations of superconducting cuprates. Ideally, the valence state should be determined essentially simultaneously with determination of elemental contents and crystal structure so that specific phases can be fully characterized. No currently available technique can do that so we have attempted to develop a technique based on the L x-ray spectrum of Cu that can be used by conventional electron microbeam instrumentation. The Cu L spectrum has distinct differences between CuO and Cu₂O that may be quantified by the ratio of peak heights in the spectra. The standard deviation of this ratio is very small compared with the difference in values. The spectra of divalent Cu in the oxide and in an alkaline earth cuprate are similar but not identical, reflecting the differences in the Cu-O polyhedra in these species. Change in the alkaline earth in the cuprate does not influence the L spectrum. The technique is potentially useful in determining valence state of Cu in more complex cuprate systems but requires use of standards in which the Cu-O polyhedra are similar to those in the unknowns.