Structural, ferroelectric, pyroelectric, and dielectric study of Bi0.5Na0.5TiO3 ceramics synthesized with precursors obtained by the sol–gel method and doped with lanthanum

Abstract

This study examines the ferroelectric, pyroelectric, and dielectric properties of La-doped bismuth sodium titanate ceramics Bi0.5Na0.51−xLaxTiO3 (BNLT), using amounts of 0–6.7 at. % La. The precursor powders used to make dense BNLT ceramics were obtained via the sol–gel method using the acetic acid route. All samples were calcined at 700 °C for 1 h and sintered at 1150 °C for 30 min in an encapsulated crucible to avoid Na and Bi volatilization yielding relative densities equal to or higher than 94%. The obtained x-ray diffraction patterns, typical of the perovskite structure, confirm the incorporation of lanthanum into the lattice, which evolved from a rhombohedral phase to a mixture of rhombohedral and cubic structures at higher concentrations. The thermogravimetry and differential scanning calorimetry results indicate that the crystallization of precursor powders of BNT takes place between 500 and 700 °C. In addition, the scanning electron microscopy micrographs reveal a decrease in grain size from 4.5 to 0.5 µm with increasing La content. The ferroelectric hysteresis curves show that the best ferroelectric properties were obtained for BNT 1.3% La, where the obtained values of remnant polarization and coercive field were Pr = 29 µC/cm2 and Ec = 39 kV/cm, respectively. At this concentration, the pyroelectric response shows a higher value, four times higher than the pyroelectric signal of pure BNT.