Structure evolution and electrical properties of lead-free Bi 0.5 Na 0.41 K 0.09 TiO 3 piezoceramics by isovalent La doping

This study investigated the structure evolution, surface morphology, dielectric properties, ferroelectric properties, piezoelectric properties, and electromechanical strain properties of lead-free (Bi 0.5− x La x )(Na 0.41 K 0.09 )TiO 3 piezoelectric ceramics. All samples were fabricated by a traditional solid-state synthesis. The effects of La 3+ -isovalent substituted on Bi 3+ -site of the Bi 0.5 Na 0.41 K 0.09 TiO 3 system were examined. The addition of La doping in the Bi 0.5 Na 0.41 K 0.09 TiO 3 ceramics induced the second phase of K 4 Ti 3 O 8 and a crystal structural change from the rhombohedral and tetragonal phase to a pseudocubic phase. All samples show similar grain morphology and dense microstructure with the average grain size around 1.33 to 1.61 μm. The dielectric curves and field-induced polarization loops of samples confirm the nonergodic-to-ergodic relaxor phase transformation, corresponding to the reduction of the temperature at the phase transition from ferroelectric to relaxor phase and the disruption of the ferroelectric properties happened in samples when increasing La 3+ content. Besides, the maximum piezoelectric constant of 139 pC/N was found in (Bi 0.48 La 0.02 )(Na 0.41 K 0.09 )TiO 3 ceramic, while the (Bi 0.46 La 0.04 )(Na 0.41 K 0.09 )TiO 3 ceramic shows a maximum strain of ~ 0.2% at a low field of 40 kV/cm.