Crystal growth and physical properties of ternary bismuth molybdenum oxides Bi_xMoO_y (x = 0.21, 0.25; y = 3 + δ)

Large purple-brown crystals of two reduced bismuth molybdenum oxides have been grown from the MoO₃-Bi₂O₃ system by electrolytic reduction of the molten salts. The unit cell parameters and the compositions have been determined by X-ray diffraction and XPS microprobe analysis, respectively. The empirical formulae were refined to Bi_0.25MoO_3.1 and Bi_0.21MoO_3.2. Transport measurements (the resistivity and the thermoelectric power) showed that both crystals are semiconductors with p-type carriers, and the thermally activated energy gaps are respectively about 0.296 eV and 0.30 eV. The EPR spectra, the XPS core-level spectra and possible structural features were also considered.