The effect of zirconia substitution on the high-temperature transformation of the monoclinic-prime phase in yttrium tantalate |
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Authors: | Quentin Flamant Mary Gurak David R Clarke |
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Affiliation: | Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA |
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Abstract: | Amorphous yttrium tantalate, as well as solid solutions containing zirconia, transform on heating to a monoclinic-prime phase and then, with further heating, to a crystalline tetragonal (T) solid solution phase at ~1450?°C. On subsequent cooling the tetragonal phase converts by a second-order displacive transformation to a different monoclinic phase not to the monoclinic-prime phase. On subsequent reheating and cooling, the phase transformation occurs between the monoclinic (M) and tetragonal phases, and the monoclinic-prime phase cannot be recovered. The limit of zirconia solubility in both the monoclinic-prime and monoclinic phases lies between 25 and 28?m/o ZrO2, consistent with previous first-principles calculations. The monoclinic-prime phase is stable up to at least 1400?°C for 100?h for zirconia concentrations from 0 to ~60?m/o ZrO2. This temperature exceeds the temperature of the equilibrium M-T phase transformation suggesting that the monoclinic-prime phase transforms directly to the tetragonal phase by a reconstructive transformation and is unaffected by the zirconia in solid solution. |
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Keywords: | Phase trasformations Yttrium tantalate Zirconia Raman spectroscopy X-ray diffraction |
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