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Fluorite and Pyrochlore Phases in the HfO2 -La2O3 -Gd2O3 Systems: Characterization and Calorimetric Study of Samples Quenched From Melts Formed by Laser Heating and Aerodynamic Levitation

Published online by Cambridge University Press:  20 February 2017

Sergey V. Ushakov ,
Alexandra Navrotsky  and
Jean A. Tangeman
Sergey V. Ushakov
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, CA 95616
Alexandra Navrotsky
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, CA 95616
Jean A. Tangeman
Affiliation:
Containerless Research, Inc., Evanston, IL 60202
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Abstract

New experimental results on pyrochlore and defect fluorite phases in HfO2-La2O3 and HfO2-Gd2O3 systems are summarized. Fluorite Hf0.5Gd0.5O1.75 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 Hf0.5La0.5O1.75 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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1122: Symposium O – Structure/Property Relationships in Fluorite-Derivative Compounds , 2008 , 1122-O01-07
Copyright
Copyright © Materials Research Society 2009

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