Superconducting phases, superstructural modulations and their relationship in La2CuO4.12 were studied. By magnetic measurements and x-ray diffraction, two superconducting phases with Tc values of 15 and 41 K were found with the structurally independent correspondents of two orthorhombic Fmmm phases. By electron diffraction, two types of superstructural modulations situated on the ab- and bc-plane were observed, with modulation vectors of 1/6a*±1/2b* and 0.18b*±(0.26-0.28)c*, respectively. These superstructural modulations were identified to be actually originated from two types of charge ordering. In addition, it is indicated that the observed ab- and bc-plane charge ordering could very possibly be correlated to the 15 and 41 K phases, respectively. For the 15 K phase, its depressed superconductivity possibly originates electronically from the ab-plane charge ordering which is compatible with the concept of the `stripe phase'.

1999 electric properties, superconductors, semiconductors electric properties, superconductors, semiconductors D 8000 -020Preparation of the Single Phase LaBa 2 Cu 3 Oy Superconductor with Tc(0) = 97 K and Suppression of the Substitution of La for Ba.-The effect of processing conditions on phase formation, solid solution range, and superconductivity for the La 1+x Ba 2−x Cu 3 Oy system is reinvestigated systematically to obtain optimum preparation conditions for La-123 superconductors. The solid solution ranges are x = 0.20-0.70 and x = 0 for La 1+x Ba 2−x Cu 3 Oy sintered and cooled in air and in N 2 , respectively. In LaBa 2 Cu 3 Oy, La can substitute for Ba, but Ba cannot substitute for La. The title compound with the highest T C of 97 K is obtained for the first time when the sample is sintered at 900 • C for 40 h in N 2 , cooled down to 305 • C in N 2 , and then treated in dry O 2 for 40-60 h. -(TAO, F.; CHE, G. C.; LIU, G. D.; ZHAO, Z. X.; WU, F.; CHEN, H.; JIA, S. L.; DONG, C.; J.