Grain morphology-dependent dielectric and piezoelectric properties of lead-free KBT ceramics

K0.5Bi0.5TiO3 ceramics with cuboid (KBT-C), rod (KBT-R), and plate (KBT-P)-shaped grains were fabricated via solid-state reaction and reactive template grain growth (using K2Ti6O13 and K0.5Bi4.5Ti4O15) methods, and the strong dependence of electrical properties on the grain morphology was demonstrated. The average grain sizes of KBT-R, KBT-P, and KBT-C were similar to 30 +/- 10 mu m, 7 +/- 1 mu m, and 350 +/- 50 nm, respectively. While the room temperature dielectric constant decreased for KBT-R (similar to 240) and KBT-P (similar to 230) from similar to 500 for KBT-C, a significant enhancement in the piezoelectric charge coefficient (d33) was noticed for KBT-R (similar to 95 pC/N) and KBT-P (similar to 105 pC/N) samples compared to that of KBT-C ceramic (similar to 60 pC/N). Accordingly, a large improvement in piezoelectric voltage coefficient (g33) of almost 300% in poled KBT-R (similar to 45 x 10-3 Vm/N) and 400% in KBT-P (similar to 54 x 10-3 Vm/N) samples over the KBT-C ceramic was obtained. Interestingly, a significantly lower activation energy (Ea) for KBT-C (similar to 0.71 eV) below the temperature of the dielectric maximum (Tm) was noticed compared to KBT-R (similar to 1.07 eV) and KBT-P (similar to 1.00 eV), suggesting a strong dependence of DC conduction on grain morphology. Furthermore, chronoamperometry measurements confirmed a mixed electronic and ionic conduction at higher temperatures in all samples. Using appropriate templates in the reactive template grain growth method allowed the fabrication of K0.5Ti0.5TiO3 ceramics with cuboid, rod, and plate-shaped grains. The piezoelectric voltage coefficient (g33) was enhanced significantly in ceramics with plate and rod-shaped grain morphologies.image