Improved dielectric and ferroelectric properties of fine-grained K0.5Na0.5NbO3 ceramics via hot-press sintering

Dense lead-free ceramics K 0.5 Na 0.5 NbO 3 were prepared via hot-press sintering in a relatively wide temperature window. Mean grain sizes of the ceramics increase from 160 nm to 720 nm due to changing the sintering parameters. All ceramics exhibit single orthorhombic phase, different domain sizes and domain morphology. Microstructure, dielectric, ferroelectric, and piezoelectric properties of the ceramics were studied systematically. For the ceramics with the mean grain size of 160 nm, the highest maximum polarization (P m ) of 30.8 μC/cm 2 , dielectric constant (ϵ r ) of 7119, piezoelectric constant (d 33 ) of 151 pC/N, and converse piezoelectric constant (d 33 *) of 291 p.m./V under the very low measurement electric field of 30 kV/cm were obtained. The excellent electrical properties are related to nano-scale fine domain configuration in fine-grained ceramics.