Phase Relations in the ZrO2-Nd2O3-Y2O3 System: Experimental Study and Advanced Thermodynamic Modeling |
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Authors: | Olga Fabrichnaya Galina Savinykh Gerhard Schreiber Hans J. Seifert |
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Affiliation: | (1) Institute of Materials Science, Technical University of Freiberg, Freiberg, Germany;(2) Present address: Institute of Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany |
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Abstract: | Phase equilibria in the ZrO2-Nd2O3-Y2O3 system at 1523-1873 K have been investigated by x-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Temperatures of phase transformations were determined by differential thermal analysis. Temperatures of invariant reactions in the ZrO2-Nd2O3 system F = A + Pyr and H = F + A were determined as 1763 and 2118 K respectively and thermodynamic parameters of phases were re-assessed. Phase transformations in ternary systems were determined at 1732 K for composition ZrO2-48.46Nd2O3-5.38Y2O3 (mol%) and at 1744 and 1881 K for composition ZrO2-79.09Nd2O3-2.75Y2O3 (mol%). They were interpreted using XRD investigation before and after DTA as Pyr + B → F, Pyr → F and A → B, respectively. The solubility of the Y2O3 in pyrochlore phase was found to exceed 10 mol%. The thermodynamic parameters of the ZrO2-Nd2O3-Y2O3 system were reassessed taking into account solubility of Y2O3 in the Nd2Zr2O7 pyrochlore phase (Pyr). It is assumed that Y3+ substitutes Nd3+ and Zr4+ in their preferentially occupied sublattices. Ternary parameter was introduced into fluorite phase (F) for better reproducing of phase equilibria. Mixing parameters were reassessed for phase A (Nd2O3 based solution), monoclinic phase B and cubic phase C (Y2O3 based solution). The isothermal sections calculated for the ZrO2-Nd2O3-Y2O3 system are in the reasonable agreement with experimental results. |
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