(K0.5Na0.5)(Nb1−xTax)O3 ceramics with a higher d33: Preparation from a two-stage microwave hydrothermal process

In this work, K0.5Na0.5Nb1−xTaxO3 (KNN1−xTx) powders with x=0.0–0.4 were synthesized by a two-stage microwave–hydrothermal (MH) method and were then used to obtain ceramics by sintering at 1090 °C for 2 h under normal atmospheric conditions. The effects of the MH temperature, holding time, two-stage synthesis procedures and Ta doping on the as-prepared powders were investigated. The phase compositions and micro-morphology of KNN1−xTx powders and ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. In addition, the density of the ceramics was measured by the Archimedes method. The results showed that homogeneous, well dispersed, crystalline pure KNN1−xTx (0≤x≤0.4) powders had been successfully synthesized by the two-stage microwave–hydrothermal synthesis, where the samples were first heated at 130 °C for 2 h and the temperature was then raised to 180 °C for 7.5 h with an alkali concentration of 6 mol/L and a K+/Na+ mole ratio of 5:1. The d33 piezoelectric constant of the KNN1−xTx ceramics sintered from the obtained powders reached its highest value of 233 pC/N at x=0.3.