Structural effect of aliovalent doping in lead perovskites

• Effective vacancy size was studied for the first time in the PLZT and PLT systems.
• The predictive model can be used to predict pseudocubic lattice constants.
• Conventionally calculated tolerance factors are calculated from this work.
• The monoclinic β angle decreases with vacancy concentration until it reaches 90°.
• The dielectric constant increases in both PLZT and PLT systems with La content.

Composition–structure relationships are needed for various applications, including lattice-matching for heteroepitaxy; however, a general model to predict lattice constants in defective perovskites is not yet available because the exact nature of A-site vacancies in perovskites remains largely unknown. In this study, it has been shown experimentally via Le Bail refinements of x-ray diffraction data that such vacancies in (Pb1−3xLa2x□x)TiO3 and (Pb1−3xLa2x□x)(Zr0.6Ti0.4)O3 have an effective   size due to both Coulombic repulsion of coordinating oxygen ions and bond relaxation. For the first time, cell volume can be predicted in this system from stoichiometry and published ionic radii data alone to within 0.2% accuracy within 0≤x≤13 compositional range and <0.3% accuracy all the way to x=13. The model may be applied to other perovskite systems and eventually provide tailored properties (magnetic, dielectric, and other) based on improved structure predictions.

The normalized effective vacancy size as a function of concentration for Pb1−3xLa2xTiO3 where the normalized effective vacancy size is unity when r□=rA(ideal) (circles=this work; squares=derived from literature values).Figure optionsDownload as PowerPoint slide