Effect of Li on the intrinsic and extrinsic contributions of the piezoelectric response in Lix(Na0.5K0.5)1-xNbO3 piezoelectric ceramics across the polymorphic phase boundary

The temperature-dependent Rayleigh behavior of polycrystalline lead-free Lix(Na0.5K0.5)1-xNbO3 ceramics was characterized to measure the reversible and irreversible piezoelectric response of different compositions with varying Li content. The results revealed that all compositions showed peak values of both reversible and irreversible piezoelectric response near the polymorphic phase boundary. Additionally, depending on the crystal structure, Li content affected the irreversible and reversible contributions. Specifically, at room temperature, there was a notable increase in the irreversible contribution with rising Li content, whereas, within the tetragonal region, the change in Li content predominantly influenced the reversible contributions, resulting in their reduction. These results are discussed in conjunction with temperature-dependent X-ray diffraction and transmission electron microscopy data, which indicated that the lattice distortion and domain structure play an important role in the temperature-dependent variation in the piezoelectric response.