| Abstrakt: |
The solid state system Bi2O3:ZrO2 has been investigated up to 28 mol% ZrO2 using Xray and neutron powder diffraction, ac impedance spectroscopy and differential thermal analysis. XRay powder diffraction has shown that a solid solution is formed with general composition Bi2 − xZrxO3 + x/2 (0.05 ≤ x ≤ 0.17) for samples calcined at 850 °C. Members of the solid solution adopt a new βBi2O3 type structure termed βIII, which is closely related to Pb2F2O. The defect structure of a sample of composition x = 0.15 has been determined by combined highresolution neutron and Xray powder diffraction. High temperature powder Xray diffraction has been used to confirm the structure of the high temperature polymorph, which is a cubic δBi2O3 analogue. In the βIIIphase, solid solution formation proceeds through an anion interstitial mechanism with respect to the hypothetical end member βIIIBi2O3, with interstitial oxide ions located in channels parallel to the caxis. The defect structure involves a pair of Zr atoms coordinated to interstitial ions in the channels. A possible conduction mechanism is proposed. Differential thermal analysis and ac impedance measurements indicate a complex phase transition to a highly conducting polymorph (σ700 = 1.02 S cm−1) at temperatures above ca. 690 °C on heating. Crystal parameters: T = 298 K, Bi1.85Zr0.15O3.075, M = 449.49, tetragonal, P42/nmc, a = 7.7206(8), c = 5.6370(6) Å, Z = 4, U = 336.0(1) Å3, Dc = 8.889(3) g cm−3; T = 1023 K, cubic, Fm3¯m, a = 5.6277(4) Å, U = 178.24(4) Å3, Z = 2, Dc = 8.379(2) g cm−3. |
