Grain-Size-Controlled (Li,Na,K)NbO3 Ceramics Using Powder Source Classified by Centrifugal Separator

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A model experiment on the grain-size-related dielectric and ferroelectric properties of lead-free Li0.04(Na0.50K0.50)0.96NbO3 piezoelectric ceramics has been carried out. Firstly, the size classification of calcined powders was achieved by a wet-type centrifugal separation technique to obtain size-classified powders with different mean particle sizes. Then, spark plasma sintering (SPS) under an identical condition at 960 °C for 10 min at a pressure of 80 MPa was performed for the size-classified powder sources to synthesize dense ceramics and control their mean grain sizes so that they ranged from 500 nm to approximately 5 μm. The results clearly allowed the distinguishing of different dielectric and ferroelectric properties on the basis of grain size. By increasing the grain size from 0.5 to 2.8 μm, the remanent polarization P_{\text{r}} gradually increases from 4.2 to 16.8 μC/cm2, but a further increase in grain size to 4.8 μm causes a decrease in P_{\text{r}} to 9.2 μC/cm2, while the coercive field E_{\text{c}} tends to increase with decreasing grain size. Our findings and the new technique to control grain size may stimulate further systematic investigation of grain-size-related properties for the development of lead-free alkali niobate piezoelectric ceramics showing excellent electrical properties.
2012-09-25