Local-structure origins of the sustained Curie temperature in (Ba,Ca)TiO3 ferroelectrics

While the lattice volume in the solid-solution Ba1-xCaxTiO3 decreases with increasing x, the Curie temperature remains unaffected, in contrast to Ba1-xSrxTiO3. We have determined the origin of this phenomenon by comparing the local structures in (Ba,Ca)TiO3 and (Ba,Sr)TiO3. Reverse Monte Carlo refinements of instantaneous atomic positions using simultaneous fitting of multiple types of experimental data (neutron total scattering, X-ray absorption fine structure, patterns of diffuse scattering in electron diffraction) reveal both ferroelectric Ca displacements and their amplification of the Ti off-centering, which mitigate the lattice-volume effects. The activity of Ca is triggered by the anomalously strained Ca-O bonds. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4802996]