Ultra-high piezoresponse in tantalum doped potassium sodium niobate single crystal

Ferroelectric materials reveal an ultra-high piezoelectric effect because of their spontaneous polarization and show high potential for applications. At present, the lead-free piezoelectric materials are in a great demand because of their environmentally friendly character, but their performance needs to be improved. Generally, in order to enhance the piezoelectric coefficients, researchers could rely on a phase boundary and/or to grow single crystals. Here, a Ta-doped (K, Na)NbO₃ (KNN) single crystal with the orthorhombic-tetragonal (O-T) phase boundary is grown via the top-seed solution growth method. Excellent piezoelectric coefficients (d₃₃ ≈ 560 pC/N via the Berlincourt method and d₃₃^* ≈ 1353 pm/V derived from strain-electric field loops) are achieved in a K_0.40Na_0.60Ta_0.41Nb_0.59O₃ single crystal. What is more, with the electric field rising from 0.5 kV/cm to 4 kV/cm, the converse d₃₃ and the strain hysteresis level improve from 580 pm/V to 640 pm/V and from 0.052 to 0.104, respectively. Our results clarify that the high d₃₃ can be attributed to the high domain density and the labyrinthine-domain structure. In addition, the electric-field-induced phase transition is also observed, which is supposed to cause the high d₃₃^*. This work not only reports the ultra-high piezoresponse of the KNN-based single crystal but also provides strong evidence for its mesoscale origin.