Synthesis, characterization, and crystallographic study of the PbO-Bi2O3-V2O5 system: Pb(3-x)Bi(2x/3)V2O8 (0.20 < or = x < or = 0.50).
Résumé
A new solid solution Pb(3-x)Bi(2x/3)V(2)O(8) (0.20 < or = x < or = 0.50), stabilizing the high-temperature gamma form of Pb(3)V(2)O(8), has been isolated in the system Pb(3)V(2)O(8)-BiVO(4). The single-crystal structure of the composition x = 0.50 (Pb(2.5)Bi(1/3)V(2)O(8)) was solved using single-crystal X-ray diffraction (XRD) technique. The compound crystallizes in the trigonal crystal system R3m (No. 166) with a palmierite structural type with a = 5.7463(3) A, c = 20.3047(12) A, V = 580.64(5) A(3), and Z = 3. The final R1 value of 0.0406 was achieved for 217 independent reflections during the structure refinement. The variable-temperature powder XRD shows the absence of any phase transition for all of the members of the solid solution in the limit of 398-80 K. The new solid solution has been characterized by neutron powder diffraction, solid-state UV-vis diffuse-reflectance spectra, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). Alternating-current impedance studies indicate conductivity on the order of 10(-4) Omega(-1) cm(-1) for Pb(2.5)Bi(1/3)V(2)O(8). The change in color of the samples from brown to yellow at high temperature was explained by XPS studies, which indicate the plausible formation of the ppm level of Bi(2)O(3) at such elevated temperature ranges.