Domain engineering in compositionally graded ferroelectric films for enhanced dielectric response and tunability

Functional materials with nonlinear dielectric response are ideally suited for telecommunications applications and threat detection in beam-steering and frequency tuning devices. Developing the theory of wedge domain in graded ferroelectrics, we present herein a quantitative model of domain evolution and dielectric response of compositionally graded ferroelectric multilayers. We show that the domain structure adapts itself to the applied electric field via domain modification. As the applied field rises, the domains are swept away layer by layer resulting in a strong nonlinear field dependence of the dielectric constant and tunability of the multilayers. There is approximately a fivefold improvement in the small-signal dielectric response and threefold enhancement in the dielectric tunability at 400 kV cm−1 in compositionally graded (001) BaxSr1−xTiO3 [BST x/(1−x)] compared to homogeneous BST layers on (001) SrTiO3 substrate. We also demonstrate that by controlling the relative thicknesses of the layers that make up the graded heterostructure, one could further enhance the dielectric response and tunability.