Built-in electric field in compositionally graded (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 thin films

Abstract

A built-in electric field was generated in compositionally graded (1 − x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ (BZT–xBCT) thin films deposited on SrRuO₃-electroded (001) SrTiO₃ single crystal substrates through pulsed laser deposition. By tailoring the gradient direction with compositionally upgraded (UG) and downgraded (DG) heterostructures, the origin of the internal bias was investigated and the structure–property relationship was also revealed. It was confirmed that the magnitude of the built-in electric field was dominated by the flexoelectric effect in the BZT–xBCT compositionally graded structure. Compared to UG multilayer, a higher remanent polarization of P_r ∼ 17 μC cm⁻² in the DG multilayer was observed. This enhancement stemmed from the retained in-plane compressive strain as confirmed by XRD results. An approximate 65% enhancement in piezoelectricity was also achieved in the DG heterostructure, which can be attributed to the larger built-in electric field.