Improved structural model of Pb-dopedγ-Bi₂O₃: (Bi_23.68Pb_0.32)(Bi_1.28Pb_0.72)O_38.48

Abstract

A polycrystalline single-phase sample with nominal composition Bi 24 PbO 37 was synthesized from Bi 2 O 3 and PbO by a high-temperature solid state reaction at 690°C for 1.5 h. The compound adopts Bi 12 SiO 20 -type structure [cubic, space group I23 (No. 197); a = 10.24957(3) Å] and was refined to R p = 7.96%, R wp = 10.4%, R exp = 8.43%, R B = 3.06%, and S = 1.23. The distributions of Pb 2+ and Bi 3+ over cationic sites based on the X-ray powder diffraction data were determined using a combination of the Rietveld refinement and bond valence calculations. The results showed that the asymmetric unit contains two mixed cation sites: the fully occupied 24f site and the partly occupied 8c site, with the unit-cell content (Bi 23.68 Pb 0.32 )(Bi 1.28 Pb 0.72 )O 38.48 . The structural constraints favor a preference of Pb 2+ ion for the 8c site, i.e. only 1.3% of Bi 3+ is substituted by Pb 2+ at the 24f site and 36% at the 8c site. At the 24f site, the cations are surrounded by 5 + 2 or in a very small amount by 5 + 1 + 2 oxide ions, forming a base bicapped square pyramid or a bicapped highly deformed octahedron, respectively. At the 8c site, the cations with three oxide ions form a trigonal pyramid with the cations at the apex.

Structural and Enhanced Optical Properties of Stabilized γ‒Bi2O3 Nanoparticles: Effect of Oxygen Ion Vacancies

“…γ-Bi 2 O 3 belongs to the sillenite family and is isomorphous to Bi 12 GeO 20 (space group I23), where Bi and Ge atoms occupy 24f and 2a symmetric sites [15]. Room temperature (RT) stabilized γ-Bi 2 O 3 was obtained through doping a foreign element at the 2a symmetric site [16,[18][19][20][21][22][23]. However, the dopant ions could hamper the intrinsic properties of γ-Bi 2 O 3 .…”

Investigation of Bi2O3-rich part of Bi2O3-PbO phase diagram

“…The fact that the single-phase Pb-doped γ-Bi 2 O 3 was obtained within such broad range of Pb concentrations confirmed the implied Bi 3+ -Pb 2+ ion isomorphous replacement, which is completely in accordance with our earlier results. 36 According to Zyryanov 42 (38) 10.257 (1) Taking into account the XRD results, we can distinguish three regions of the final phase composition: region A for found in Bi 2 O 3 -PbO phase diagram. 31 The thermal behaviour can be discussed within the same three regions obtained from XRD results, i.e., A, B and C. (Table II).…”