Mixed conductor, electrochemical device, and method of preparing mixed conductor

A method of preparing a mixed conductor, the method comprising:

• providing a mixture comprising an element A precursor, a titanium precursor, and an element G precursor,
• wherein the element A precursor provides a monovalent cation, and the element G precursor provides at least one of a monovalent cation, a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, or a hexavalent cation, with the proviso that G is not Ti or Cr;
• and
• heat-treating the mixture to prepare the mixed conductor,
• wherein the mixed conductor is represented by Formula 1
• A4±xTi5−yGzO12−δ Formula 1
• wherein, in Formula 1,
• A is a monovalent cation,
• G is at least one of a monovalent cation, a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, or a hexavalent cation, with the proviso that G is not Ti or Cr, and
• 0<x<2, 0.3<y<5, 0<z<5, and 0<δ≤3,
• wherein the mixed conductor comprises a phase having a spinel-type crystal structure, and
• wherein, in an X-ray diffraction spectrum of the mixed conductor, a peak intensity ratio of an intensity of a peak corresponding to a (111) crystal plane at a diffraction angle 2θ of 18°±2.5° to an intensity of a peak at a diffraction angle 2θ of 23.5°±2.5° is 0.001 to 1.