Conductivity in lead substituted bismuth yttrate fluorites

Abstract

The di-substituted bismuth oxide based oxide ion conducting electrolyte system Bi 2.5+x Pb 0.5 YO 5.75+3x/2-δ (x = 0, 1 and 2) has been investigated by X-ray powder diffraction, a.c. impedance spectroscopy, thermal analysis and X-ray photoelectron spectroscopy. δ-Bi 2 O 3 type phases are observed for all compositions studied and showed no obvious changes in structure up to 850°C. Results from thermal analysis, and the thermal variation of the lattice parameter indicate a small degree of reduction occurs at high temperature, which is preserved on quenching. XPS results suggest this involves reduction of bismuth and lead cations. This reduction is reversed on heating at intermediate temperatures. The redox reactions appear to be correlated to a degree of curvature in the Arrhenius plot of conductivity. Measurement of transference numbers indicate that these materials are predominantly ionic conductors, with conductivity values at high temperature comparable with mono-substituted analogues.

Defect structure in δ-Bi5PbY2O11.5

“…5 and is compared with previously obtained results from X-ray diffraction on heating and cooling in air. 12 There are signicant differences in the results from the two experiments, which can be attributed to small differences in oxygen stoichiometry, resulting from the different experimental conditions, underlining the sensitivity of this system to changes in oxygen partial pressure. The results from the present study, collected under vacuum, feature two linear regions above 150 C, with a transition at around 450 C. In the X-ray study in air, a signicant difference was seen in the heating and cooling curves below 450 C, associated with small changes in oxygen stoichiometry.…”

“…[5][6][7][8][9][10] We have recently investigated the ternary system Bi 2 O 3 -PbO-Y 2 O 3 , where Bi 3+ is substituted for a combination of subvalent and isovalent cations (Pb 2+ and Y 3+ ), leading to d-Bi 2 O 3 type structures, with nominal vacancy concentrations higher than in the stoichiometric parent compound. 12 Yttrium substitution for bismuth in Bi 2 O 3 is well known to yield highly conducting cubic d-type phases over a relatively large composition range [13][14][15][16][17][18] and much of this work is reviewed by Sammes et al 8 In contrast, despite the close similarity of the Bi 3+ and Pb 2+ cations, in terms of their stereochemistries (dominated by the 6s 2 lone pair) and polarizabilities, lead substitution for bismuth does not lead to the appearance of the d-type phase at low temperatures. 19 However, in ternary systems such as Bi 2 O 3 -MO x -PbO (M ¼ Ca, Y, Er and La), preservation of the d-type phase to room temperature is observed.…”

“…[20][21][22][23][24] In a previous study we examined compositions in the Bi 2 O 3 -PbO-Y 2 O 3 system of general formula Bi 2.5+x Pb 0.5 YO 5.75+3x/2 (x ¼ 0, 1 and 2), which showed the d-phase structure. 12 These phases exhibited very high conductivities (ca. 0.4 S cm À1 at 800 C), with ionic transference numbers close to unity.…”

“…Thermal variation of cubic lattice parameter, a, for d-Bi 5 PbY 2 -O 11.5 , showing data collected using X-ray diffraction on heating in air (red circles), on cooling in air (blue circles) and using neutron diffraction on heating under vacuum (green squares). X-ray data taken from Borowska-Centkowska et al12 …”

Structure–property relationships in fluorite-type Bi2O3–Yb2O3–PbO solid-electrolyte materials

“…It is also possible to use a combination of metal oxides – “double doping” – to quench-in the Bi 2 O 3 -based fluorite-type phase. Examples include the ternary oxide systems Bi–Dy–W (Jiang et al , 2002), Bi–Er–W (Watanabe and Sekita, 2005), Bi– Ln –Te (Mercurio et al , 1990), Bi– Ln –V (Portefaix et al , 1997), Bi–Ca–Pb (Drache et al , 1992), Bi–Y–Pb (Borowska-Centkowska et al , 2014), and Bi–La–Pb (Webster et al , 2011).…”