Low-temperature hydro/solvothermal synthesis of Ta-modified K0.5Na0.5NbO3 powders and piezoelectric properties of corresponding ceramics

Highlights: → Hydro/solvothermal provides a milder temperature condition than hydrothermal. → Ta content and poling temperature affect the piezoelectric properties greatly. → The optimum sintering temperatures of ceramics are reduced at least 150 oC. -- Abstract: K0.5Na0.5Nb1-xTaxO3 (KNNTx, x = 0-0.4) powders were synthesized by a novel hydro/solvothermal method at a low reaction temperature (180 oC) and the corresponding ceramics were obtained by normal sintering. Compared with conventional solid-state reaction technique, the optimal sintering temperatures of these ceramics were reduced at least 150 oC. Crystalline structures and surface morphologies were analyzed by X-ray diffraction and scanning electron microscopy. The excellent piezoelectric properties could be obtained by selecting poling temperature near the orthorhombic-tetragonal polymorphic phase transition temperature region. Ta-modified KNN ceramics exhibited better piezoelectric properties than those of pure KNN, and the piezoelectric coefficient d33 showed the maximum value of 156 pC/N for KNNT0.3 ceramics. In addition, the sintering temperature for maximum d33 value differed from that for maximum density. The present hydro/solvothermal method provides a new potential route for preparing KNN-based materials at relatively low temperature.