Large piezoelectric properties induced by doping ionic pairs in BaTiO ₃ ceramics

The high piezoelectric properties of piezoelectric ceramics are typically obtained by inducing a phase transition between two ferroelectric phases, using either the morphotropic phase boundary (MPB) or the polymorphic phase transition (PPT). Here we demonstrate that neither the MPB nor the PPT is necessary to achieve high piezoelectric properties. Our results show that the optimized distribution of Li⁺-Al³⁺ pairs parallel to the [0 0 1] direction, as found in our xLiAlSiO₄/BaTiO₃ (xLAS/BT) lead-free piezoelectric ceramic system prepared from ordinary raw materials by conventional solid-state reaction sintering, can generate a large piezoelectric constant (d₃₃) of 378 pC/N when x = 7.5 mol.%. The d₃₃ value of the 7.5 mol.% LAS/BT ceramic is more than three times that of the pure BT ceramic. The distortion connected to the proposed Li⁺-Al ³⁺ pairs locally creates unit cells of less than tetragonal symmetry, and these low-symmetry cells can be responsible for the high piezoelectric response. The high-temperature stability testing reveals that these doped ceramics are usable at temperatures as high as 120 °C. This piezoelectric mechanism coming from the doping ionic pairs provides a new method to achieve large piezoelectric properties in a wide range of ABO₃-type perovskite systems.