Ultrafast sintering of BNT-8BT: Densification, grain-growth kinetics and piezoelectric properties

Bi₀.₅Na₀.₅TiO₃–8BaTiO₃ (BNT–8BT) is an eco-friendly lead-free relaxor ferroelectric material with large electrostrain, while undergoing phase instability and grain coarsening due to long, high-temperature exposure in conventional sintering. Here, ultrafast high-temperature sintering (UHS) was applied to investigate the densification behavior, grain-growth kinetics, and piezoelectric properties of BNT–8BT. Compared with conventional sintering, UHS-sintered samples processed for 60 s showed a similar relative density of 93.4% and a much smaller grain size of 2.0 μm, corresponding to approximately 48% grain refinement. The distinct UHS thermal history enabled substantial densification while limiting accumulated coarsening, resulting in finer, more uniform grains; Arrhenius analyses yielded model-dependent apparent activation energies for UHS of 242 kJ·mol⁻¹ for n = 2 and 359 kJ·mol⁻¹ for n = 3. Furthermore, the UHS-sintered samples exhibited a d₃₃ of 155 pC/N, comparable to that of the CS specimen at a similar relative density despite its substantially finer micron-scale microstructure.