XPS Study of Superconducting $LiTi_2O_4$ and $LiTi_{2-x}Cu_{x}O_4$ Sol-Gel Derived Powders and Thin Films

In this work X-ray photoelectron studies of lithium titanate and copper doped lithium titanate are presented. Both, powder and thin films samples were prepared by sol-gel method. After preparation, the samples were heated in argon atmosphere at various temperatures in a range from 500 °C to 600 °C for 20 h. The crystalline structure of the samples was investigated by X-ray diffraction, while the oxidation states of the elements were examined by X-ray photoelectron spectroscopy method. X-ray diffraction measurements confirmed spinel phase of all manufactured samples. However it is well known that electrical and superconducting properties of lithium titanate are strongly correlated not only with structure, but also with oxidation state of Ti ions. X-ray photoelectron spectroscopy investigations revealed mixture of $Ti^{3+}$ and $Ti^{4+}$ ions, although the $Ti^{3+}$/$Ti^{4+}$ ratio is much smaller than $1/2$ needed for superconductivity. In this work dependence between calcination temperature as well as amount of Cu dopant and $Ti^{3+}$/$Ti^{4+}$ proportion are reported.