Subcoercive field dielectric response of 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) thin film: Peculiar third harmonic signature of phase transitions and residual ferroelectricity

Subcoercive field non-linearities in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) (BCTZ 50/50) thin film elaborated using pulsed laser deposition are studied using permittivity and phase angle of the third harmonic measurements as a function of the AC measuring field E A C and temperature. The global phase transition temperature T max for which the permittivity is maximum, decreases from 330 to 260 K when E A C increases. Rayleigh analysis of the AC field dependence of the relative permittivity shows a regular decrease in the domain wall motion contributions as temperature increases up to T max and an even more pronounced decrease above T max. This measurement reveals that the ferroelectric behavior subsists 70 K above the global phase transition. The phase angle of the third harmonic at temperatures below 275 K is characteristic of a conventional ferroelectric and from 275 K to T max = 330 K of a relaxor. Above T max, the thin film exhibits a peculiar phase angle of the third harmonic, which consists of − 180 ° → − 225 ° → + 45 ° → 0 ° instead of the − 180 ° → − 90 ° → 0 ° found for relaxor. This peculiar behavior is observed only on heating and is tentatively attributed to changes in the correlations between polar nanoregions.