Characterization of heavily Cu-doped La2CuO4+delta by transmission electron microscopy and electron energy loss spectroscopy

The techniques of transmission electron microscopy and electron energy loss spectroscopy (EELS) have been used for characterizing heavily Cu-doped pol ycrystalline La2CuO4.003 (LCO) samples. Semiquantitative and spatially reso lved EELS analysis reveals that Cu may be doped into LCO lattice and that C u doping introduces effectively holes into the sample. At room temperature, the LCO grains were found to phase separate into hole-poor and hole-rich g rains, and in hole-rich grains holes were found to have a strong tendency t o concentrate and form one-dimensional static ordering with planar domain w all promoted by high-energy electron beam. Two kinds of modulation vectors have been found, they are 1/4b* +/- 1/3c* (with a wavelength similar to 18. 9 Angstrom) and 1/6a* +/- 1/3b* +/- 1/2c* (with a wavelength similar to 12. 7 Angstrom). At lower temperatures, sharper and higher-order superlattice r eflections were observed, indicating an enhanced charge ordering, and super lattice reflections originating from 1/4b* +/- 1/3c* were found to dominate those originating from 1/6a* +/- 1/3b* +/- 1/2c* with a shorter modulation period.