The correlation between permittivity frequency dispersion and depoling process upon heating was investigated in Zr⁴⁺-modified 0.75BiFeO₃–0.25BaTiO₃ (BF–BZT) ceramics. The temperature-dependent permittivity 𝜀_r(𝑇) and the piezoelectric coefficient 𝑑₃₃ for poled samples were measured under heating conditions to clarify the depolarization mechanism. The results indicate that the poling temperature plays a crucial role in the domains' alignment process, as expected. The temperature-dependent permittivity frequency dispersion and depolarization behaviours may have same origin. The aligned domains' break up into random state/nanodomains at depoling temperature (𝑇 _d), which causes strong frequency dependence of the permittivity, simultaneously, induces the loss of piezoelectricity. It suggests that the temperature-dependent permittivity measurements method is a simple way to determine the depolarization temperature.

It is well known that domains and crystal structure control the physical properties of ferroelectrics. The ex-situelectric field-dependent structural study, carried out in unpoled/poled crushed powder and bulk samples for (Li$_{0.5}$Nd$_{0.5}$)$^{2+}$ modified 0.95Bi$_{0.5}$Na$_{0.5}$TiO$_3$−0.05BaTiO$_3$ solid solution, established a correlation between domain configuration andcrystal structure variation. Under applying electric field, the smeared ferroelectric phase structure due to coherence diffractioneffect of nanodomains reappeared due to obsolescent coherence effect associated with the field-induced ordered nanodomains.The macroscopic characterizing techniques of domain configuration such as dielectric constant spectroscopy and X-raydiffraction measurement can provide a basis for understanding the correlation between domains configuration and crystalstructure in ferroelectric ceramics.