Lanthanum-Induced Morphotropic Phase Boundary in BiFeO3-BaTiO3-Based Lead-Free Piezoelectric Ceramics

0.71Bi(1.05(1-x))La(x)Fe(0.98)Ga(0.02)O(3)-0.29BaTiO(3) + 0.1wt%MnO2 ceramics are fabricated via a traditional solid-state reaction route. Rietveld refinement analysis of X-ray diffraction data shows that all the studied ceramics consist of rhombohedral and tetragonal phases. The La-free samples are dominated by rhombohedral phase, the proportion of which, however, gradually decreases with the addition of La. And in 0.005 <= x <= 0.02, the ceramics have approximately equal proportions of rhombohedral and tetragonal phases, showing the characteristics of typical morphotropic phase boundary (MPB). The optimal piezoelectric properties (d(33) = 178 pC N-1 and k(p) = 0.31) are achieved at x = 0.005, owing to the MPB. A more apparent relaxor behavior is found to be induced with the addition of La. Furthermore, the ceramics also exhibit good insulation properties and high-temperature stability of piezoelectric properties, which is very important for practical uses, especially for those in high-temperature environments.