Chemical renormalization of the paraelectric–ferroelectric phase transition in PbTiO3-BiB0.5′B0.5″O3 solid solutions with tetragonal symmetry

The effect of the type of B-site substituent on the development of the ferroelectric state in the tetragonal part of the composition-temperature (x-T) diagram of (1-x)PbTiO3-xBi B 0.5 ′ B 0.5 ″O3 solid solutions is analyzed by applying the second harmonic generation (SHG) method and Raman spectroscopy to three compounds with B 0.5 ′ B 0.5 ″ = Mg0.5Ti0.5, Ni0.5Ti0.5, and Ni0.5Zr0.5, having nearly the same tolerance factor and unit-cell tetragonality, at temperatures up to ∼1000 K. The results reveal the importance of B-site divalent dopants with an isotropic electron configuration for the enhancement of local symmetry breaking at the A site and a consequent increase in the Curie temperature at small x, regardless of the macroscopic tetragonality with respect to PbTiO3.