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

Abstract

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 EAC and temperature. The global phase transition temperature Tmax for which the permittivity is maximum, decreases from 330 to 260 K when EAC 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 Tmax and an even more pronounced decrease above Tmax. 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 Tmax=330 K of a relaxor. Above Tmax, 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.