Fluorite and pyrochlore phases in the HfO2 -La2O 3 -Gd2O3 systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation

Sergey V. Ushakov; Alexandra Navrotsky; Jean A. Tangeman

doi:10.1557/proc-1122-o01-07

Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation

Sergey V. Ushakov, Alexandra Navrotsky, Jean A. Tangeman

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

1 Scopus citations

Abstract

New experimental results on pyrochlore and defect fluorite phases in HfO₂-La₂O₃ and HfO₂-Gd ₂O₃ systems are summarized. Fluorite Hf _0.5Gd_0.5O_1.75 was formed by containerless melting and quenching. Melts with 25-65 mol% La₂O₃ did not produce any fluorite-type phases, but pyrochlores with cell parameters 10.74 to 10.86 Å. The fluorite phase of Hf_0.5La_0.5O _1.75 can be formed on crystallization of an amorphous precursor from aqueous precipitation. Both La- and Gd- fluorite phases transform to ordered pyrochlore on annealing at 1450°C. The enthalpies of formation from oxides are -107 ±5 kJ/mol for Hf₂La₂O₇ and -49 ±5 kJ/mol for Hf₂Gd₂O₇ as measured by high-temperature solution calorimetry. Further experiments are needed to elucidate the nature of stabilization of fluorite phase in thin films and powders. Occurrence of disordered phases in thin films, nanoparticles and radiation damaged materials is discussed.

Original language	English (US)
Title of host publication	Structure/Property Relationships in Fluorite-Derivative Compounds
Publisher	Materials Research Society
Pages	12-17
Number of pages	6
ISBN (Print)	9781615677627
DOIs	https://doi.org/10.1557/proc-1122-o01-07
State	Published - 2008
Externally published	Yes
Event	2008 MRS Fall Meeting - Boston, MA, United States Duration: Dec 1 2008 → Dec 5 2008

Publication series

Name	Materials Research Society Symposium Proceedings
Volume	1122
ISSN (Print)	0272-9172

Conference

Conference	2008 MRS Fall Meeting
Country/Territory	United States
City	Boston, MA
Period	12/1/08 → 12/5/08

ASJC Scopus subject areas

General Materials Science
Condensed Matter Physics
Mechanics of Materials
Mechanical Engineering

Access to Document

10.1557/proc-1122-o01-07

Cite this

Ushakov, S. V., Navrotsky, A., & Tangeman, J. A. (2008). Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation. In Structure/Property Relationships in Fluorite-Derivative Compounds (pp. 12-17). (Materials Research Society Symposium Proceedings; Vol. 1122). Materials Research Society. https://doi.org/10.1557/proc-1122-o01-07

Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation. / Ushakov, Sergey V.; Navrotsky, Alexandra; Tangeman, Jean A.
Structure/Property Relationships in Fluorite-Derivative Compounds. Materials Research Society, 2008. p. 12-17 (Materials Research Society Symposium Proceedings; Vol. 1122).

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

Ushakov, SV , Navrotsky, A & Tangeman, JA 2008, Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation. in Structure/Property Relationships in Fluorite-Derivative Compounds. Materials Research Society Symposium Proceedings, vol. 1122, Materials Research Society, pp. 12-17, 2008 MRS Fall Meeting, Boston, MA, United States, 12/1/08. https://doi.org/10.1557/proc-1122-o01-07

Ushakov SV , Navrotsky A, Tangeman JA. Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems: Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation. In Structure/Property Relationships in Fluorite-Derivative Compounds. Materials Research Society. 2008. p. 12-17. (Materials Research Society Symposium Proceedings). doi: 10.1557/proc-1122-o01-07

Ushakov, Sergey V. ; Navrotsky, Alexandra ; Tangeman, Jean A. / Fluorite and pyrochlore phases in the HfO₂ -La₂O ₃ -Gd₂O₃ systems : Characterization and calorimetric study of samples quenched from melts formed by laser heating and aerodynamic levitation. Structure/Property Relationships in Fluorite-Derivative Compounds. Materials Research Society, 2008. pp. 12-17 (Materials Research Society Symposium Proceedings).

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abstract = "New experimental results on pyrochlore and defect fluorite phases in HfO2-La2O3 and HfO2-Gd 2O3 systems are summarized. Fluorite Hf 0.5Gd0.5O1.75 was formed by containerless melting and quenching. Melts with 25-65 mol% La2O3 did not produce any fluorite-type phases, but pyrochlores with cell parameters 10.74 to 10.86 {\AA}. The fluorite phase of Hf0.5La0.5O 1.75 can be formed on crystallization of an amorphous precursor from aqueous precipitation. Both La- and Gd- fluorite phases transform to ordered pyrochlore on annealing at 1450°C. The enthalpies of formation from oxides are -107 ±5 kJ/mol for Hf2La2O7 and -49 ±5 kJ/mol for Hf2Gd2O7 as measured by high-temperature solution calorimetry. Further experiments are needed to elucidate the nature of stabilization of fluorite phase in thin films and powders. Occurrence of disordered phases in thin films, nanoparticles and radiation damaged materials is discussed.",

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AB - New experimental results on pyrochlore and defect fluorite phases in HfO2-La2O3 and HfO2-Gd 2O3 systems are summarized. Fluorite Hf 0.5Gd0.5O1.75 was formed by containerless melting and quenching. Melts with 25-65 mol% La2O3 did not produce any fluorite-type phases, but pyrochlores with cell parameters 10.74 to 10.86 Å. The fluorite phase of Hf0.5La0.5O 1.75 can be formed on crystallization of an amorphous precursor from aqueous precipitation. Both La- and Gd- fluorite phases transform to ordered pyrochlore on annealing at 1450°C. The enthalpies of formation from oxides are -107 ±5 kJ/mol for Hf2La2O7 and -49 ±5 kJ/mol for Hf2Gd2O7 as measured by high-temperature solution calorimetry. Further experiments are needed to elucidate the nature of stabilization of fluorite phase in thin films and powders. Occurrence of disordered phases in thin films, nanoparticles and radiation damaged materials is discussed.

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