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Effect of Aliovalent Dopants on the Kinetics of Phase Transformation and Ordering in RE 2 O 3 ‐Bi 2 O 3 (RE = Yb, Er, Y, or Dy) Solid Solutions
Author(s) -
Fung Kuan Zong,
Chen Jong,
Virkar Anil V.
Publication year - 1993
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1993.tb03961.x
Subject(s) - dopant , kinetics , phase (matter) , conductivity , materials science , analytical chemistry (journal) , superstructure , electrical resistivity and conductivity , crystallography , doping , chemistry , thermodynamics , physics , optoelectronics , organic chemistry , quantum mechanics , chromatography , electrical engineering , engineering
Bi 2 O 3 ‐based cubic solid solutions containing 20% Er 2 O 3 undergo transformation to a rhombohedral phase when annealed at temperatures 635°C. This transformation is generally very sluggish and is accompanied by a decrease in conductivity. The kinetics of this transformation were enhanced by the addition of CaO and suppressed by the addition of ZrO 2 . The time constants for transformation kinetics at 600°C for CaO‐doped and undoped samples were ∼55 and ∼330 h, respectively, and the incubation periods ranged between ∼20 and ∼2000 h depending upon the dopant type, its concentration, and the temperature. This result is rationalized on the premise that cation interstitials are more mobile compared to cation vacancies. The same samples, originally cubic of CaF 2 type, when annealed below about 600°C for a short period of time (a few hours) undergo a degradation in conductivity without a change in XRD patterns. The kinetics of this conductivity decay were observed to be significantly faster than the kinetics of cubic → rhombohedral phase transformation. A similar degradation of conductivity was also observed in samples containing other stabilizers such as Y 2 O 3 , Dy 2 O 3 , and Yb 2 O 3 . The kinetics of conductivity decay without the formation of the rhombohedral phase were also found to depend upon the presence of aliovalent dopants. Specifically, ZrO 2 suppressed this decay. Electron diffraction showed the formation of a superstructure in samples annealed at temperatures <600°C. Analysis of the diffraction patterns suggests that the structure corresponds to a doubling of the unit cell with the ordering of cations responsible for the origin of the superstructure. The decay in conductivity in the ordered state is attributed to the expected differences in bonding between oxygen ions and the two different cations, Bi and RE.