Influence of the electron concentration on the superconducting properties of the spinel system Li1-yTi2O4



In the spinel system Li1-y Ti2O4 the Li content was reduced by oxidative extraction by means of a solution of I2 as well as Br2 in CH3CN or by oxygen. The extraction is associated with a transition of Ti3+ to Ti4+: the system is Li1-y Ti3+1-yTi4+1+y O4. Consequently, with increasing y the charge carrier concentration decreases from the starting value of 0.5 electrons/Ti ion for LiTi2O4. The extraction proceeds in two steps. At the beginning, the Ti2O4 framework remains intact and the transition to superconductivity increases with decreasing charge carrier concentration to a maximal value of 13.2 K. Separated by a two-phase region for medium extraction levels for higher y values, a Li depleted material of approximate composition Li0.3Ti2O4 is obtained. The crystal structure of Li0.3Ti2O4 can be deduced from the original spinel lattice by a partial Ti migration from 16d to 16c and 8 a sites (space group Fd3m). Consequently, the Ti2O4 framework of Li0.3Ti2O4 is disconnected and the material is no longer superconducting.