Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates

Sergey V. Ushakov; Alexandra Navrotsky; Jean A. Tangeman; Katheryn B. Helean

doi:10.1111/j.1551-2916.2007.01592.x

Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates

Sergey V. Ushakov, Alexandra Navrotsky, Jean A. Tangeman, Katheryn B. Helean

Research output: Contribution to journal › Article › peer-review

48 Scopus citations

Abstract

Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO₂-La₂O₃ (-Gd₂O ₃) systems. All melts crystallized upon quenching in oxygen. Hf ₂La₂O₇ pyrochlore and Gd_0.5Hf _0.5O_1.75 fluorite phases were identified. Gd _0.5Hf_0.5 O_1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO₂-La₂O₃ melts contained 31.6-34.2 mol% La₂O₃. The unit cell parameter increased linearly with La content from 10.736 to 10.789 Å. Drop solution calorimetric experiments were performed in 3Na₂O · 4MoO ₃ melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are -107.0 ± 5.0 kJ/mol for Hf₂La ₂O₇ and -48.8 ± 4.7 kJ/mol for Hf ₂Gd₂O₇. The enthalpy of the pyrochlore-fluorite phase transition in Hf₂Gd₂O₇ is 23.6 ± 3.1 kJ/mol.

Original language	English (US)
Pages (from-to)	1171-1176
Number of pages	6
Journal	Journal of the American Ceramic Society
Volume	90
Issue number	4
DOIs	https://doi.org/10.1111/j.1551-2916.2007.01592.x
State	Published - Apr 2007
Externally published	Yes

ASJC Scopus subject areas

Ceramics and Composites
Materials Chemistry

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title = "Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates",

abstract = "Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO2-La2O3 (-Gd2O 3) systems. All melts crystallized upon quenching in oxygen. Hf 2La2O7 pyrochlore and Gd0.5Hf 0.5O1.75 fluorite phases were identified. Gd 0.5Hf0.5 O1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO2-La2O3 melts contained 31.6-34.2 mol% La2O3. The unit cell parameter increased linearly with La content from 10.736 to 10.789 {\AA}. Drop solution calorimetric experiments were performed in 3Na2O · 4MoO 3 melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are -107.0 ± 5.0 kJ/mol for Hf2La 2O7 and -48.8 ± 4.7 kJ/mol for Hf 2Gd2O7. The enthalpy of the pyrochlore-fluorite phase transition in Hf2Gd2O7 is 23.6 ± 3.1 kJ/mol.",

author = "Ushakov, {Sergey V.} and Alexandra Navrotsky and Tangeman, {Jean A.} and Helean, {Katheryn B.}",

year = "2007",

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doi = "10.1111/j.1551-2916.2007.01592.x",

language = "English (US)",

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T1 - Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates

AU - Ushakov, Sergey V.

AU - Navrotsky, Alexandra

AU - Tangeman, Jean A.

AU - Helean, Katheryn B.

PY - 2007/4

Y1 - 2007/4

N2 - Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO2-La2O3 (-Gd2O 3) systems. All melts crystallized upon quenching in oxygen. Hf 2La2O7 pyrochlore and Gd0.5Hf 0.5O1.75 fluorite phases were identified. Gd 0.5Hf0.5 O1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO2-La2O3 melts contained 31.6-34.2 mol% La2O3. The unit cell parameter increased linearly with La content from 10.736 to 10.789 Å. Drop solution calorimetric experiments were performed in 3Na2O · 4MoO 3 melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are -107.0 ± 5.0 kJ/mol for Hf2La 2O7 and -48.8 ± 4.7 kJ/mol for Hf 2Gd2O7. The enthalpy of the pyrochlore-fluorite phase transition in Hf2Gd2O7 is 23.6 ± 3.1 kJ/mol.

AB - Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO2-La2O3 (-Gd2O 3) systems. All melts crystallized upon quenching in oxygen. Hf 2La2O7 pyrochlore and Gd0.5Hf 0.5O1.75 fluorite phases were identified. Gd 0.5Hf0.5 O1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO2-La2O3 melts contained 31.6-34.2 mol% La2O3. The unit cell parameter increased linearly with La content from 10.736 to 10.789 Å. Drop solution calorimetric experiments were performed in 3Na2O · 4MoO 3 melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are -107.0 ± 5.0 kJ/mol for Hf2La 2O7 and -48.8 ± 4.7 kJ/mol for Hf 2Gd2O7. The enthalpy of the pyrochlore-fluorite phase transition in Hf2Gd2O7 is 23.6 ± 3.1 kJ/mol.

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Energetics of defect fluorite and pyrochlore phases in lanthanum and gadolinium hafnates

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