Investigation on preparation of Na0.5K0.5NbO3 nanoparticles by microwave heating method

Lead-free piezoelectric (K0.5Na0.5)NbO3 nanoparticles were successfully synthesized via microwave heating. The phase structure, morphology and particle size of the samples synthesized by microwave and conventional method were characterized by TG-DSC, XRD and FTIR. Microwave thermal effect and the reaction mechanism were analyzed. The results revealed that single-phase (K0.5Na0.5)NbO3 nanoparticles could be obtained at relatively low temperature and short time of 650 °C for 10 min by microwave method. The particles possess an orthorhombic crystal structure and the composition is consistent with stoichiometric ratio. The obtained particles are fine, uniform and with little agglomeration. With the microwave synthesis temperature reducing from 800 °C to 650 °C, the average diameter of particles decreases from 600 nm to 100 nm and weakens the agglomeration. The possible formation mechanism of (K0.5Na0.5)NbO3 nanoparticles affected by microwave thermal effect was proposed. Due to the selective microwave heating, low temperature eutectic reaction between Na+, K+ solid solution and Nb2O5 occurs and the intermediate phase (K, Na)2Nb4O11 is formed. Subsequently, as the reaction temperature increased, high temperature eutectic reaction arises and the Na2Nb4O11 and K4Nb6O17 intermediate phases are formed. Ultimately, all the intermediate phases disappear and (K0.5Na0.5)NbO3 nanoparticles are synthesized.