Phase evolution and oxide ion conduction behavior of Dy1−xBixO1.5 (0.00 ≤ x ≤ 0.50) composite system

Abstract

A series of Dy_1−xBi_xO_1.5 (0.00 ≤ x ≤ 0.50) compositions were prepared by conventional solid state reactions of Bi₂O₃ and Dy₂O₃. X-ray diffractometry, ac-impedance spectroscopy and scanning electron microscopy were used to characterize the structure and properties of these compositions. All the compositions except x = 0.44 exist as composites of either rhombohedral and C-type rare-earth oxide phases or rhombohedral and fluorite type phases. At x = 0.44, a rhombohedral phase is observed which can broadly be explained on a sub cell with unit cell parameters: a_sub = 3.7728(1) Å and c_sub = 9.5541(5) Å, V = 117.77(1) ų, Z = 3. The exact structure is a super lattice of this unit cell. The unit cell of the super- and sub structures are related as: a_super = b_super ∼ 4 × a_sub and c_super ∼ 2 × c_sub. The studied Bi₂O₃–Dy₂O₃ systems showed an oxide anionic conductivity and the conductivity increases with the increase in Bi concentration as well as temperature. Typical activation energies of all compositions are within 1.1 to 1.2 eV. At 800 K, the highest conductivity is observed for the composition Dy_0.50Bi_0.50O_1.50 in the series. The observed maximum conductivity is lower than δ-Bi₂O₃, but significantly higher than the stabilized zirconia.