The Effect of Composition Gradient on Microdomain Structure and the Macro-Ferroelectric/Piezoelectric Properties

Internal fields caused by strain gradient, composition gradient (CG), and space charges have significant influences on micro and macro properties of ferroelectrics. Here, we report the relationship among composition gradient, microdomain structure, and macroscopic ferroelectric/piezoelectric properties. Three KTa1–xNbxO3 samples with the same Curie temperature Tc = 39 °C and different CGs are designed and investigated. As CG decreases, the scale of domains decreases from ∼10 μm to 200 nm, and the spontaneous polarizations orientate more randomly, which leads to a smaller ratio of lattice content c to a (c/a). Furthermore, dielectric constant and d33 increases dramatically from 6000 to 11 000 and from 203 to 345 pC N–1, respectively. This relationship is important for prospective applications due to its controllability of microdomains and polarization states. In addition, we reveal that CG and composition fluctuation induce internal fields (Ein) and resilience, respectively, leading to the frequency-dependent biased and standard double polarization–electric field (P–E) loops. Moreover, the existence of CGs drives the formation of different size domains by Ein, which provides a way to adjust ferroelectric and piezoelectric properties by controlling CG. As well, it is important for the study of flexoelectric on continuous CG bulk materials.