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In light of environmental issues, the lead-free ferroelectric single crystal K(Ta 1- x Nb x )O 3 (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 ( d 33 = 156 pC/N, d 15 = 155 pC/N) and dielectric constants (ε 33 T ∼ 2337). Additionally, tensor matrix transformation techniques were utilized to analyze the directional dependence of the piezoelectric ( d 33 * ), dielectric (ε 33 T * ), elastic ( s 33 E * ) constants, and electromechanical coupling coefficient ( k 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.