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Massive Transformation in the Y 2 O 3 ‐Bi 2 O 3 System
Author(s) -
Fung Kuan Zong,
Virkar Anil V.,
Drobeck David L.
Publication year - 1994
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.1151-2916.1994.tb09768.x
Subject(s) - dopant , materials science , phase (matter) , oxide , analytical chemistry (journal) , crystallography , metal , solid solution , grain boundary , diffusion , grain growth , mineralogy , doping , grain size , chemistry , thermodynamics , metallurgy , microstructure , physics , optoelectronics , organic chemistry , chromatography
Cubic solid solutions in the Y 2 O 3 ‐Bi 2 O 3 system with ∼25% Y 2 O 3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition‐invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo‐graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y 2 O 3 ‐Bi 2 O 3 system is a massive transformation. Samples of composition 25% Y 2 O 3 ‐75% Bi 2 O 3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO 2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO 2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO 2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10 −10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys.