Synthesis of suboxides, Ti₈(Sn_xBi_1−x)O₇and Ti_11.17(Sn_0.85Bi_0.15)₃O₁₀, using a Bi flux and their crystal structures

Single crystals of Ti₈(Sn_xBi_1−x)O₇(x = 0.41, 0.65, 0.72, 0.935) were obtained by heating mixtures of Bi 3.0 mmol, Ti 0.5 mmol, TiO₂0.5 mmol, and Sn 0.03, 0.07, 0.20, 1.00 mmol at 900 °C and by slow cooling from this temperature. The crystal structures of Ti₈(Sn_xBi_1−x)O₇(orthorhombic, space group Cmmm, a = 7.85283(13)–7.83817(15) Å, b = 16.8007(2)–16.7741(3) Å, c = 3.01479(5)–2.99499(5) Å) were analyzed by single crystal X-ray diffraction. The x values of Ti₈(Sn_xBi_1−x)O₇in the single crystals were larger than the mole fractions Sn/(Sn + Bi) of the starting mixtures, indicating that the crystals preferentially contained Sn. The cell volumes of Ti₈(Sn_xBi_1−x)O₇decreased from 397.750(11) ųto 393.776(13) ųwith increasing x, which corresponded to the size difference between Sn and Bi atoms. Single crystals of Ti_11.17(Sn_0.85Bi_0.15)₃O₁₀(cubic, space group Fm3¯m, a = 13.5890(4) Å) were also found in the sample prepared from the starting mixture containing 1.00 mmol Sn. These suboxides are specific by combinations of structural futures of oxides and intermetallics. A polycrystalline bulk sample which mainly consisted of Ti₈(Sn_0.77Bi_0.23)O₇was fabricated by heating the compact of a starting materials mixture with the stoichiometric composition at 900 °C for 12 h. The electrical resistivity of the bulk sample was 7.0 × 10⁻⁶Ωm at 300 K and monotonically decreased with decreasing temperature.