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Elastic Properties of Calcium Oxide Perovskites

Published online by Cambridge University Press:  01 February 2011

Nancy L. Ross
Affiliation:
Department of Geological Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, USA
Ross J. Angel
Affiliation:
Department of Geological Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, USA
Jennifer Kung
Affiliation:
Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA
Tracey D. Chaplin
Affiliation:
Department of Chemistry, University College London, Gower Street, London WC1E 6BT, U.K.
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Abstract

The equations of state and axial moduli of the CaBO3 perovskites (B=Zr,Sn,Ti,Ge) and CaFeO2.5 with the brownmillerite structure have been determined using high-pressure, singlecrystal X-ray diffraction. The bulk modulus-specific volume relationship for the Ca-perovskites is nonlinear, with CaSnO3 and CaZrO3 displaying anomalous stiffening (higher bulk moduli) than previously reported and predicted [1,2]. The axial moduli of the a- and c-axes decrease steadily by ∼30% from the least-distorted of the Pbnm perovskites, CaGeO3, to the most distorted, CaZrO3, while the b-axis shows little change. The net result is a threefold increase in the anisotropy of the axial moduli of CaSnO3 and CaZrO3 (∼21%) relative to CaGeO3 and CaTiO3 (∼4-8%). The bulk modulus of CaFeO2.5 falls significantly below the trend for the stoichiometric perovskites. The introduction of 1/6 vacancies on the oxygen positions softens the perovskite structure by 25%.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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