Synthesis of (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders by high temperature mixing method under hydrothermal conditions

A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders. The influence of Ta doping and K+/(K+ + Na+) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O3 ceramics from the obtained powders were investigated. The piezoelectric coefficient (d33), electromechanical coupling coefficient (kp), dielectric constant (ɛr), and remnant polarization (Pr) of the sample sintered at 1180 °C show optimal values of 210 pC/N, 34.0%, 2302, and 19.01 μC/cm2, respectively.