Optimizing K(0.5)Na(0.5)NbO(3) Single Crystal by Engineering Piezoelectric Anisotropy

K(0.5)Na(0.5)NbO(3) is considered as one of the most promising lead-free piezoelectric ceramics in the field of wearable electronics because of its excellent piezoelectric properties and environmental friendliness. In this work, the temperature-dependent longitudinal piezoelectric coefficient [Formula: see text] was investigated in K(0.5)Na(0.5)NbO(3) single crystals via the Landau–Ginzburg–Devonshire theory. Results show that the piezoelectric anisotropy varies with the temperature and the maximum of [Formula: see text] deviates from the polar direction of the ferroelectric phase. In the tetragonal phase, [Formula: see text] parallels with cubic polarization direction near the tetragonal-cubic transition region, and then gradually switches toward the nonpolar direction with decreasing temperatures. The maximum of [Formula: see text] in the orthorhombic phase reveals a distinct varying trend in different crystal planes. As for the rhombohedral phase, slight fluctuation of the maximum of [Formula: see text] was observed and delivered a more stable temperature-dependent maximum [Formula: see text] and its corresponding angle θ(max) in comparison with tetragonal and orthorhombic phases. This work not only sheds some light on the temperature-dependent phase transitions, but also paves the way for the optimization of piezoelectric properties in piezoelectric materials and devices.