Compositional heterogeneity enhancing the flexoelectric response of BaTiO3 -based ceramics

Flexoelectric effect possesses potential applications in electromechanical conversion, and the flexoelectric coefficient of ferroelectrics is greatly larger than that of ordinary dielectrics. Among the ferroelectrics, BaTiO3 (BT) ceramics are lead-free materials, also receive a high flexoelectric response. However, it is still inferior to the piezoelectric response of lead-based piezoelectric materials. Herein, we inhomogeneously added x wt. % ZrO2 into BT ceramics (x wt. % ZrO2/BT ceramics, and x =0.05, 0.5, 1, 2) to enhance the flexoelectric response of BaTiO3-based ceramics. The largest effective flexoelectric coefficients (μρ) of ∼ 800 μC/m at room temperature (RT) and ∼ 1500 μC/m near Curie temperature (TC ∼ 127 °C) were abtained in 0.5 wt. % ZrO2/BT ceramics, which is ∼ 6.7 times and ∼ 3.9 times larger than that of the as-prepared BT ceramics at RT and near TC (∼ 131.7 °C here) respectively. Although TC of the 0.5 wt. % ZrO2/BT ceramics decreases compared with that of BT ceramics, its higher μρ than that of the as-prepared BT ceramics maintains a wide temperature range, extending to 160 °C. The enhancement of the μρ of the 0.5 wt. % ZrO2/BT ceramics is largely attributed to the compositional heterogeneity between grain boundaries gathered with irregular paraelectric and orthorhombic Ba(Zr, Ti)O3, and grains which are tetragonal BaTiO3. The compositional heterogeneity is easily shaped into a strain gradient (namely a flexoelectric polarization), which plays a promoting effect on the flexoelectric coefficients.