TY - JOUR
T1 - Perovskite solid solutions along the NaNbO 3-SrTiO 3 join
T2 - Phase transitions, formation enthalpies, and implications for general perovskite energetics
AU - Xu, Hongwu
AU - Navrotsky, Alexandra
AU - Su, Yali
AU - Balmer, M. Lou
N1 - Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.
PY - 2005/4/5
Y1 - 2005/4/5
N2 - Perovskite solid solutions along the NaNbO 3-SrTiO 3 join have been synthesized using the sol-gel and solid-state sintering methods. XRD analysis indicates that as Sr+Ti content increases, the perovskite structure changes from the orthorhombic to tetragonal and to cubic. The enthalpies of formation from the constituent oxides (ΔH f,ox° and from the elements (ΔH f,el°) have been determined by drop solution calorimetry into molten 3Na 2O·4MoO 3 at 974 K. The formation enthalpy ΔH f,ox° becomes less exothermic with increasing Sr+Ti content, suggesting a destabilization effect of the substitution, Na + + Nb 5+ → Sr 2+ + Ti 4+ on the perovskite structure with respect to the constituent oxides. The trend of decreasing thermodynamic stability with decreasing structural distortion (relative to the ideal cubic structure) is opposite to that seen in most ABO 3 perovskites. We interpret this behavior in terms of the dominance of acid-base chemistry, expressed by the ionic potential ratio of B to A cation (z/r) B/(z/r) A, in determining phase stability. This approach can be applied to other perovskite systems. Moreover, the enthalpic variation with Sr+Ti content is nearly linear, and thus the enthalpies of the morphotropic transitions across the series are rather small.
AB - Perovskite solid solutions along the NaNbO 3-SrTiO 3 join have been synthesized using the sol-gel and solid-state sintering methods. XRD analysis indicates that as Sr+Ti content increases, the perovskite structure changes from the orthorhombic to tetragonal and to cubic. The enthalpies of formation from the constituent oxides (ΔH f,ox° and from the elements (ΔH f,el°) have been determined by drop solution calorimetry into molten 3Na 2O·4MoO 3 at 974 K. The formation enthalpy ΔH f,ox° becomes less exothermic with increasing Sr+Ti content, suggesting a destabilization effect of the substitution, Na + + Nb 5+ → Sr 2+ + Ti 4+ on the perovskite structure with respect to the constituent oxides. The trend of decreasing thermodynamic stability with decreasing structural distortion (relative to the ideal cubic structure) is opposite to that seen in most ABO 3 perovskites. We interpret this behavior in terms of the dominance of acid-base chemistry, expressed by the ionic potential ratio of B to A cation (z/r) B/(z/r) A, in determining phase stability. This approach can be applied to other perovskite systems. Moreover, the enthalpic variation with Sr+Ti content is nearly linear, and thus the enthalpies of the morphotropic transitions across the series are rather small.
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U2 - 10.1021/cm047785i
DO - 10.1021/cm047785i
M3 - Article
AN - SCOPUS:18144393020
SN - 0897-4756
VL - 17
SP - 1880
EP - 1886
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 7
ER -