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Thermochemistry of Rare Earth Perovskites

Published online by Cambridge University Press:  30 June 2016

Dawei Feng  and
Alexandra Navrotsky
Dawei Feng
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
Alexandra Navrotsky*
Affiliation:
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
*
*Corresponding author email address: [email protected] (A. Navrotsky). Tel.: (530) 752-3292; fax: (530) 752-9307
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Abstract

The rare earth (RE) mineral loparite with the chemical composition (RE, Na, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3 is the principal ore of the light rare earth elements (LREE) as well as niobium and tantalum. The enthalpies of formation of RE0.67-xNa3xTiO3 (RE = La, Ce) and Ca1-2xNaxLaxTiO3 from oxides and elements of lanthanum and cerium perovskites and their solid solutions have been obtained using high temperature oxide melt solution calorimetry. RE0.67-xNa3xTiO3 (RE = La, Ce) perovskites become more stable relative to oxide components as sodium content increases. Na0.5Ce0.5TiO3 and Na0.5La0.5TiO3 can be considered stable endmembers in natural loparite minerals. For perovskite solid solutions Ca1-2xNaxLaxTiO3, the enthalpies of formation from the constituent oxides $\Delta {\rm{H}}_{{\rm{f}},\,{\rm{ox}}}^^\circ$ become more exothermic with increasing Na+La content, suggesting a stabilizing effect of the substitution 2Ca2+ → Na+ + La3+ on the perovskite structure. The trend of increasing thermodynamic stability with decreasing structural distortion is similar to that seen in many other ABO3 perovskites.

Keywords

calorimetrychemical substitutioncrystallographic structure
Type
Articles
Information
MRS Advances , Volume 1 , Issue 38: Materials Design , 2016 , pp. 2695 - 2700
Copyright
Copyright © Materials Research Society 2016 

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