Achieving High Piezoelectric Performance Across Multidomains Design in K(Ta,Nb)O₃-Based Lead-free Single Crystals

In light of environmental issues, the lead-free ferroelectric single crystal K(Ta_1-<i>x</i>Nb_<i>x</i>)O₃ (KTN) has attracted considerable interest due to its excellent piezoelectric properties. This research focus on improving the piezoelectric performance of KTN by engineering domains through polarization in the [011]_c direction. The full-matrix parameters of KTN crystals after polarization along the [011] direction were determined. The finding reveal that KTN polarized in the nonspontaneous polarization direction [011]_c exhibits higher piezoelectric constants (<i>d</i>₃₃ = 156 pC/N, <i>d</i>₁₅ = 155 pC/N) and dielectric constants (ε₃₃^<i>T</i> ∼ 2337). Additionally, tensor matrix transformation techniques were utilized to analyze the directional dependence of the piezoelectric (<i>d</i>₃₃^*), dielectric (ε₃₃^<i>T</i>*), elastic (<i>s</i>₃₃^<i>E</i>*) constants, and electromechanical coupling coefficient (<i>k</i>₃₃^*). The results indicate that these constants reach their maximum values along the polarized [011]_c direction. A comparison of the experimental polarization values in the [011]_c direction with those calculated for a single-domain state, demonstrates that ferroelectric domains in KTN crystals contribute significantly to the piezoelectric properties. Finally, polarized light microscopy was used to conduct a detailed analysis of the domain structure in KTN single crystals, revealing various orientations and sizes of domain walls. This research offers strategies for optimizing piezoelectric performance.