Effects of Processing Parameters on the Synthesis of (K0.5Na0.5)NbO3Nanopowders by Reactive High-Energy Ball Milling Method

The effects of ball milling parameters, namely, the ball-to-powder mass ratio and milling speed, on the synthesis of (K0.5Na0.5)NbO3nanopowders by high-energy ball milling method from a stoichiometric mixture containing Na2CO3, K2CO3, and Nb2O5were investigated in this paper. The results indicated that the single crystalline phase of (K0.5Na0.5)NbO3was received in as-milled samples synthesized using optimized ball-to-powder mass ratio of 35 : 1 and at a milling speed of 600 rpm for 5 h. In the optimized as-milled samples, no remaining alkali carbonates that can provide the volatilizable potassium-containing species were found and (K0.5Na0.5)NbO3nanopowders were readily obtained via the formation of an intermediate carbonato complex. This complex was mostly transformed into (K0.5Na0.5)NbO3at temperature as low as 350°C and its existence was no longer detected at spectroscopic level when calcination temperature crossed over 700°C.

Direct Synthesis of (K0.5Na0.5)NbO3Powders by Mechanochemical Method

The synthesis and structural properties of lead-free piezoelectric (K0.5Na0.5)NbO3powders prepared by mechanochemical method using Nb2O5, K2CO3, and Na2CO3as starting materials were reported. X-ray diffraction, infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy were used to characterize the prepared samples. Results showed that, for the first time, by selecting the milling speed of 600 rpm and the ball-to-powder weight ratio of 35 : 1 as milling parameters, pure (K0.5Na0.5)NbO3crystalline phase was obtained directly in the as-milled samples after 5 h of milling time. The existence of a carbonato complex betweenCO32−and Nb5+ions as an intermediate species of the formation of (K0.5Na0.5)NbO3was also found.