Electro-Optic g Coefficients of Pb-Containing Oxygen-Octahedra Ferroelectrics: Ceramic (Pb, Ba)(Zr, Ti)O3

Electro-optic g coefficients, which relate induced birefringence and polarization via the quadratic electro-optic effect, are found to have the value g11−g12 ≈ g44 ≈ 0.011±0.008 m4/C2 for 12 oxygen-octahedra ferroelectrics having Pb in the perovskite A site. Measurements on four such ferroelectrics were made using ceramic compositions of the series (Pb, Ba) (Zr, Ti)O3 which has a diffuse phase transition and a maximum quadratic electro-optic coefficient of R33−R13=3.4×10−16 m2/V2 at room temperature. To explain why the measured g is 10 times smaller than those compiled and computed by DiDomenico and Wemple for other oxygen-octahedra ferroelectrics, the optical-index dispersion energy εd and the birefringence dispersion constant K were determined. Values of εd=25 eV and K=−0.5 are as found for the other ferroelectrics. A smaller g must therefore arise from a smaller polarization potential coefficient β, which is defined with respect to energy shifts and polarization of the BO6 perovskite octahedra. Such a definition can lead to a smaller β in Pb-containing ferroelectrics because the higher polarizability and displacement of the Pb ion contribute polarization which is not properly accounted for. In any case, the g coefficient can no longer be considered as a universal constant for oxygen-octahedra materials.