Composition dependent order-disorder transition in Nd Zr1−O2−0.5 pyrochlores: A combined structural, calorimetric and ab initio modeling study
| Autor: | Ph. Kegler, Christian Schreinemachers, George Beridze, Alexandra Navrotsky, Andrey Bukaemskiy, Felix Brandt, Sarah Finkeldei, Anna Shelyug, Dirk Bosbach, Victor L. Vinograd, Piotr M. Kowalski |
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| Rok vydání: | 2017 |
| Předmět: |
Phase transition
Materials science Polymers and Plastics Enthalpy Configuration entropy Metals and Alloys Pyrochlore Ab initio Oxide Thermodynamics 02 engineering and technology Calorimetry engineering.material 021001 nanoscience & nanotechnology 01 natural sciences Electronic Optical and Magnetic Materials Crystallography chemistry.chemical_compound chemistry 0103 physical sciences Ceramics and Composites engineering 010306 general physics 0210 nano-technology Entropy (order and disorder) |
| Zdroj: | Acta Materialia. 125:166-176 |
| ISSN: | 1359-6454 |
| DOI: | 10.1016/j.actamat.2016.11.059 |
| Popis: | The order-disorder phase transition in the Nd x Zr 1−x O 2−0.5x system is studied by complementary techniques which include wet chemical synthesis of a series of compositions with various Nd/Zr ratios with the final annealing at 1873 K, X-ray diffraction, oxide melt solution calorimetry and ab initio thermodynamic modeling. Our structural data indicate the transition from ordered to disordered pyrochlore at x ∼0.31 at a temperature of 1873 K. Our calorimetric data show a transition enthalpy of ∼30 kJ/mol, which corresponds to an entropy of disordering of ∼16 J/K/mol. The latter value is significantly smaller than the configurational entropy of transition computed under the assumption of complete disorder in a fluorite phase, indicating a substantial degree of order remaining in the fluorite phase at the temperature of synthesis. The considered phases are computed ab initio using a series of special quasi-random structures that emulate the complete or partial disorder. The results of our calculations and thermodynamic modeling are in good agreement with the measured lattice parameters, the Nd content at the order-disorder transition, and the measured formation and transformation enthalpies. Thus our combined experimental and modeling results provide valuable insight into the disordering of this pyrochlore phase and of other pyrochlore materials. |
| Databáze: | OpenAIRE |
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