High piezoelectric activity in (Na,K)NbO3 based lead-free piezoelectric ceramics: Contribution of nanodomains

The origin of high piezoelectric response in (Na0.52K0.48-x)(Nb0.92-xSb0.08)O-3-xLiTaO(3) lead-free ceramics was investigated by looking into the composition-dependent domain morphology by means of transmission electron microscopy. Nanodomains of alternate orthorhombic and tetragonal domains with a width of 20-50 nm were surprisingly observed but only for compositions near polymorphic phase coexistence zone. The formation of nanodomain morphology was considered to result from the reduction of the domain wall energy owing to the vanishing of the polar anisotropy, which ultimately induced enhanced piezoelectric properties. The result indicated that nanodomains are not proprietary features of traditional Pb-based piezoelectric ceramics with a morphotropic phase boundary. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624704]