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Cubic‐to‐Tetragonal Displacive Transformation in Gd 2 O 3 –Bi 2 O 3 Ceramics
Author(s) -
Su Pomin,
Virkar Anil V.,
Hubbard Camden R.,
Cavin O. Burl,
Porter Wallace D.
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.tb03974.x
Subject(s) - tetragonal crystal system , materials science , monoclinic crystal system , differential scanning calorimetry , crystallite , crystallography , annealing (glass) , electrical resistivity and conductivity , ceramic , analytical chemistry (journal) , mineralogy , crystal structure , chemistry , metallurgy , thermodynamics , physics , engineering , chromatography , electrical engineering
Gd 2 O 3 ‐doped Bi 2 O 3 polycrystalline ceramics containing between 2 and 7 mol% Gd 2 O 3 were fabricated by pressureless sintering powder compacts. The as‐sintered samples were tetragonal at room temperature. Hightemperature X‐ray diffraction (XRD) traces showed that the samples were cubic at elevated temperatures and transformed into the tetragonal polymorph during cooling. On the basis of conductivity measurements as a function of temperature and differential scanning calorimetry (DSC), the cubic → tetragonal as well as tetragonal → cubic → teansition temperatures were determined as a function of Gd 2 O 3 concentration. The cubic → tetragonal transformation appears to be a displacive transformation. It was observed that additions of ZrO 2 as a dopant, which is known to suppress cation interdiffusion in rare‐earth oxide–Bi 2 O 3 systems, did not suppress the transition, consistent with it being a displacive transition. Annealing of samples at temperatures 660°C for several hundred hours led to decomposition into a mixture of monoclinic and rhombohedral phases. This shows that the tetragonal polymorph is a metastable phase.