  The evolution from superconducting LiTi2O4-delta to insulating Li4Ti5O12 thin
films has been studied by precisely adjusting the oxygen pressure during the
sample fabrication process. In the superconducting LiTi2O4-delta films, with
the increase of oxygen pressure, the oxygen vacancies are filled, and the
c-axis lattice constant decreases gradually. With the increase of the oxygen
pressure to a certain critical value, the c-axis lattice constant becomes
stable, which implies that the Li4Ti5O12 phase comes into being. The process of
oxygen filling is manifested by the angular bright-field images of the scanning
transmission electron microscopy techniques. The temperature of
magnetoresistance changed from positive and negative shows a non-monotonous
behavior with the increase of oxygen pressure. The theoretical explanation of
the oxygen effects on the structure and superconductivity of LiTi2O4-delta has
also been discussed in this work.
