Structural origin of strongly diffused ferroelectric phase transition in Ba(Ti, Zr)O3-based ceramics

A significant broadening of the ferroelectric phase transition is an inherent characteristic of disordered polar systems, such as technologically important materials based on relaxor ferroelectrics. The origins of diffusion of the dielectric maximum are usually associated with chemical and structural heterogeneity, leading to local deviations of the Curie temperature in polar nanoregions giving rise to relaxor behavior. In this work, based on the results of crystal structure, dielectric, and ferroelectric properties investigation, we report a surprising broadening enhancement of the ferroelectric phase transition in (1- x)BaTi _0.95Zr _0.05O ₃- xPbTiO ₃ ceramics with x = 0.30. The values of its diffuseness parameters are similar to or even exceed those of common relaxor ferroelectrics, even though the studied ceramics does not demonstrate any frequency-dependent shift of dielectric maxima. Symmetry-mode analysis of the atomic displacements in the tetragonal phases provides direct evidence of the concentration-induced crossover between B-site and A-site driven ferroelectricity at x = 0.30. Structure-property correlations between polar distortion amplitudes, dielectric and ferroelectric behavior are observed, suggesting an increase in structural stiffness in the crossover region. This work shows a new structural mechanism of strongly diffused phase transition in ferroelectrics that consists of the interplay between atomic displacements of the A and B cations of the perovskite structure and, in principle, is not associated with the atomic disorder as such.