Thermochemistry of Rare Earth Perovskites. Issue 38 (30th June 2016)

• Record Type: Journal Article
• Authors: Feng, Dawei; Navrotsky, Alexandra
• Is Part Of: MRS advances. Volume 1:Issue 38(2016)
• Page Start: 2695
• Page End: 2700
• Publication Date: 2016-06-30
• Subjects: calorimetry, -- chemical substitution, -- crystallographic structure; Electrical engineering -- Congresses; Physics -- Congresses; Materials -- Research -- Congresses; Materials science -- Congresses; 620.11
• DOI: 10.1557/adv.2016.489
• Languages: English
• ISSNs: 2059-8521

Abstract

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-x Na3x TiO3 (RE = La, Ce) and Ca1-2x Nax Lax TiO3 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-x Na3x TiO3 (RE = La, Ce) perovskites become more stable relative to oxide components as sodium content increases. Na0.5 Ce0.5 TiO3 and Na0.5 La0.5 TiO3 can be considered stable endmembers in natural loparite minerals. For perovskite solid solutions Ca1-2x Nax Lax TiO3, 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 2Ca 2+ → Na + + La 3+ on the perovskite structure. The trend of increasing thermodynamic stability with decreasing structural distortion is similar to that seen in many other ABO3 perovskites.