Cubic-to-Tetragonal Displacive Transformation in Gd2O3–Bi2O3 Ceramics |
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Authors: | Pomin Su Anil V Virkar Camden R Hubbard O Burl Cavin Wallace D Porter |
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Affiliation: | Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112;Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 |
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Abstract: | Gd2O3-doped Bi2O3 polycrystalline ceramics containing between 2 and 7 mol% Gd2O3 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 Gd2O3 concentration. The cubic → tetragonal transformation appears to be a displacive transformation. It was observed that additions of ZrO2 as a dopant, which is known to suppress cation interdiffusion in rare-earth oxide–Bi2O3 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. |
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