| Autor: |
Ushakov, Sergey V., Hong, Qi-Jun, Pavlik, Alfred, van de Walle, Axel, Navrotsky, Alexandra |
| Zdroj: |
Chemistry of Materials; May 2024, Vol. 36 Issue: 9 p4868-4876, 9p |
| Abstrakt: |
Erbium and thulium sesquioxides are the only lanthanide oxides that exhibit premelting cubic-hexagonal (C–H) phase transformation. The enthalpies of phase transitions and fusion were measured for the first time using a differential thermal analyzer calibrated by melting Y2O3. C–H transition enthalpies of Er2O3and Tm2O3are 48 ± 7 and 69 ± 7 kJ/mol at 2301 ± 10 and 2384 ± 14 °C, with enthalpies of fusion 59 ± 9 and 69 ± 8 kJ/mol at 2419 ± 12 and 2416 ± 20 °C, respectively. The mean linear thermal expansion of cubic phases up to transformation temperature was determined from synchrotron diffraction on laser heated aerodynamically levitated Er2O3and Tm2O3as (8.80 ± 0.02) and (8.74 ± 0.01) × 10–6/K, respectively. The experimental results were used to benchmark ab initio molecular dynamic computations which provided an isobaric heat capacity of 178 ± 5 J/mol/K for both liquid oxides at 2427–3027 °C. The comparable enthalpy values for premelting C–H transformation and fusion corroborate a high degree of dynamic disorder in the H phase suggesting superplasticity and ionic conductivity. The melting temperature for cubic Er2O3and Tm2O3obtained from ab initio molecular dynamic computations aligns with the experimentally measured temperature for the C–H transition. |
| Databáze: |
Supplemental Index |
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