SYNCHROTRON X-RAY-POWDER DIFFRACTION STUDY OF ELECTROCHEMICALLY OXIDIZED LA2CUO4-XNDXCUO4+DELTA(DELTA AND LA2)

We report the results of synchrotron X-ray powder diffraction studies of a series of electrochemically oxidized samples of La2CuO4+delta. Th ese materials exhibit several structural phases depending upon the val ue of delta, including one with a superconducting transition temperatu re (T-c) of 32 K, and two others with T(c)s near 45 K. The observation of two phases with such high T(c)s, which has not previously been rep orted, is made possible in this study by the high resolution of synchr otron X-ray diffraction. We have also made preliminary observations of several phases of composition La2-xNdxCuO4+delta, and find these mate rials to be single phase for large values of delta. It may be that the random potential introduced by Nd3+ substitution for La3+ serves to p in the interstitial oxygen ions and prevents the formation of ordered superstructures for high values of delta.