The effects of oxygen in spinel oxide Li(1+x)Ti(2−x)O(4−δ) thin films

The evolution from superconducting LiTi(2)O(4-δ) to insulating Li(4)Ti(5)O(12) thin films has been studied by precisely tuning the oxygen pressure in the sample fabrication process. In superconducting LiTi(2)O(4-δ) films, with the increase of oxygen pressure, the oxygen vacancies are filled gradually and the c-axis lattice constant decreases. When the oxygen pressure increases to a certain critical value, the c-axis lattice constant becomes stable, which implies that the sample has been completely converted to Li(4)Ti(5)O(12) phase. The two processes can be manifested by the angular bright-field images of the scanning transmission electron microscopy techniques. The transition temperature (T(ch)) of magnetoresistance from the positive to the negative shows a nonmonotonic behavior, i.e. first decrease and then increase, with the increase of oxygen pressure. We suggest that the decrease T(ch) can be attributed to the suppressing of orbital-related state, and the inhomogeneous phase separated regions contribute positive MR and thereby lead to the reverse relation between T(ch) and oxygen pressure.