Evolution of structure and electrical properties with lanthanum content in [(Bi1/2Na1/2)0.95Ba0.05]1-xLaxTiO3 ceramics

Lead-free perovskite [(Bi1/2Na1/2)0.95Ba0.05]1-xLaxTiO3 (x = 0.00 ~ 0.10) ceramics were fabricated via the solid state reaction method and their crystal structures and electrical properties were systematically studied. Transmission electron microscopy examination reveals a transition from a rhombohedral R3c phase with micron-sized complex domains to a mixture of rhombohedral R3c and tetragonal P4bm phases with nanodomains as La content was increased. X-ray diffraction analysis on bulk samples, however, indicates a pseudocubic structure in La-doped compositions. Electrical poling seems to transform the pseudocubic structure to a rhombohedral phase in compositions with 0.00 \u3c x \u3c 0.03. With La addition, the depolarization temperature (Td) is observed to decrease and the dielectric constant (εr) within 100 ~ 350 oCbecomes more temperature independent, promising for applications in high-temperature capacitors. Electric field-induced polarizations and strains display complex changes with respect to La concentration, with the highest strain of 0.35 % achieved in the composition x = 0.04 under 70 kV/cm at room temperature. The piezoelectric coefficient d33 initially increases with La content, reaching a maximum value of 151 pC/N in the composition x = 0.02, and then diminishes