Synthesis and Crystal Structure of Suboxide Solid Solutions, Ti_12-δGa_xBi_3-xO₁₀

Single crystals of suboxide solid solutions Ti_12-δGa_xBi_3-xO₁₀ (x = 1.42-1.74; δ = 0.77-0.62) were prepared at 900 °C with a Bi flux. Crystal structure analysis by X-ray diffraction (XRD) revealed that the solid solutions are isostructural with Ti_12-δSn₃O₁₀ (cubic, space group Fm3̅m). The cell parameter a decreases from 13.5616(3) to 13.5402(5) Å with increasing Ga content, x, while the total valence electron number of Ti_12-δGa_xBi_3-xO₁₀ is maintained at 117.1 by decreasing Ti defects, δ. Stella octangula is formed by sharing of the edges of four supertetrahedra composed of O-centered Ti tetrahedra and trigonal bipyramids (oxide part). Another superpolyhedron is formed by sharing of the pyramidal planes of Ga/Bi-centered, Ti-monocapped square antiprisms (intermetallic part). These two parts are incorporated in the structure. A polycrystalline bulk of a solid solution with x = 2.01 and δ = 0.67 [a = 13.53772(13) Å] was synthesized by reaction sintering at 950 °C from a mixture of Ti, TiO₂, Bi₂O₃, and Ga₂O₃. The resistivities measured for the bulk were (2.2-2.4) × 10^-5 Ω m in the temperature range from 10 to 300 K.