Modulation structure and phase transformation in a Cu-rich La-Cu-O oxide

The modulation structure in the be plane of a phase-separated Cu-rich La2Cu O4.003 oxide was studied using transmission electron microscopy. Upon an el ectron beam irradiation at 93 K, a phase transformation from superconductin g phase to antiferromagnetic phase was observed and identified based on the analysis of the different reflection conditions for the two space groups o f the two phases, i.e., D-2h(23) or Fmmm for the superconducting phase and D-2h(18) or Bmab for the antiferromagnetic phase. For the superconducting p hase it is found that the modulation vector changes from 0.041[06 (8) over bar]* toward 0.027[04 (8) over bar]* during the electron-beam irradiation. Electron energy-loss spectroscopy results are also presented showing that t he Cu-rich La2CuO4.003 oxide has indeed phase-separated into hole-rich supe rconducting phase and hole-poor antiferromagnetic insulating phase. [S0163- 1829(99)00505-6].