Synchrotron x-ray powder diffraction study of electrochemically oxidized La2CuO4+δ and La2−x NdxCuO4+δ

We report the results of synchrotron X-ray powder diffraction studies of a series of electrochemically oxidized samples of La2CuO4 + δ. These materials exhibit several structural phases depending upon the value of δ, including one with a superconducting transition temperature (Tc) of 32 K, and two others with Tcs near 45 K. The observation of two phases with such high Tcs, which has not previously been reported, is made possible in this study by the high resolution of synchrotron X-ray diffraction. We have also made preliminary observations of several phases of composition La2−xNdxCuO4+δ, and find these materials to be single phase for large values of δ. It may be that the random potential introduced by Nd3+ substitution for La3+ serves to pin the interstitial oxygen ions and prevents the formation of ordered superstructures for high values of δ.