Phase-Composition-Dependent Piezoelectric and Electromechanical Strain Properties in (Bi^sub 1/2^Na^sub 1/2^)TiO^sub 3-Ba(Ni^sub 1/2^Nb^sub 1/2^)O^sub 3^ Lead-Free Ceramics

• Published in: Journal of the American Ceramic Society 2015-03, Vol.98 (3), p.811
• Main Authors: Li, Feng, Zuo, Ruzhong, Zheng, Donggeng, Li, Longtu
• Format: Article
• Language: English
• Subjects: Ceramics; Dielectric properties; Dispersion; Electric fields; Ferroelectrics; Mechanical properties; Perovskite
• ISSN: 0002-7820; 1551-2916

New lead-free perovskite solid solution ceramics of (1 - x)(Bi1/2Na1/2)TiO3-xBa(Ni1/2Nb1/2)O3[(1-x)BNT-xBNN,x = 0.02-0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d33~121 pC/N and kp~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.