In the spinel system Li,-,Ti204 the Li content was reduced by oxidative extraction by means of a solution of I, as well as Br, in CH3CN or by oxygen. The extraction is associated with a transition of Ti3+ to Ti4+: the system is L i , -Y T i~! Y T i~~Y 0 4 . Consequently, with increasing y the charge carrier concentration decreases from the starting value of 0.5 electrons/Ti ion for LiTi204. The extraction proceeds in two steps. At the beginning, the Ti20, framework remains intact and the transition to superconductivity increases with decreasing charge carrier concentration to a maximal value of 13.2K. Separated by a two-phase region for medium extraction levels for higher y values, a Li depleted material of approximate composition Lio,,Ti,04 is obtained. The crystal structure of Lio.3Ti,0, can be deduced from the original spinel lattice by a partial Ti migration from 16d to 16c and 8a sites (space group Fd3m). Consequently, the Ti,04 framework of Lio,3Ti,0, is disconnected and the material is no longer superconducting.
1991 electric properties, superconductors, semiconductors electric properties, superconductors, semiconductors D 8000 45 -020 Superconducting Properties of the Lead-Containing 2212 Phase Bi1.75Pb0. 25Sr2CaCu2O8+z with Tc in the Range 70-98 K. -It is demonstrated that the superconducting transition temp. Tc of the title compound can be raised from about 70 K, measured after air quenching, to about 98 K by a controlled post-treatment (annealing at 650 • C in argon). Because there are no significant changes in the oxygen content after postannealing, it is concluded that a more favorable ordering of oxygens in the lattice is produced by the post-treatment. -(RYGULA, M.; RENTSCHLER, T.; SCHLICHENMAIER, M.; WISCHERT, W.; KEMMLER-SACK, S.; J.
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