Large Piezoelectric Effect in Pb-Free Ceramics

We report a non-Pb piezoelectric ceramic system Ba(Ti0.8Zr0.2)O-3-(Ba0.7Ca0.3)TiO3 which shows a surprisingly high piezoelectric coefficient of d(33)similar to 620 pC/N at optimal composition. Its phase diagram shows a morphortropic phase boundary (MPB) starting from a tricritical triple point of a cubic paraelectric phase (C), ferroelectric rhombohedral (R), and tetragonal (T) phases. The high piezoelectricity of the MPB compositions stems from the composition proximity of the MPB to the tricritical triple point, which leads to a nearly vanishing polarization anisotropy and thus facilitates polarization rotation between << 001 >> T and << 111 >> R states. We predict that the single-crystal form of the MPB composition of the present system may reach a giant d(33)=1500-2000 pC/N. Our work may provide a new recipe for designing highly piezoelectric materials (both Pb-free and Pb-containing) by searching MPBs starting from a TCP.