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

Abstract

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 ∼30 ± 10 μm, 7 ± 1 μm, and 350 ± 50 nm, respectively. While the room temperature dielectric constant decreased for KBT‐R (∼240) and KBT‐P (∼230) from ∼500 for KBT‐C, a significant enhancement in the piezoelectric charge coefficient (d33) was noticed for KBT‐R (∼95 pC/N) and KBT‐P (∼105 pC/N) samples compared to that of KBT‐C ceramic (∼60 pC/N). Accordingly, a large improvement in piezoelectric voltage coefficient (g33) of almost 300% in poled KBT‐R (∼45 × 10−3 Vm/N) and 400% in KBT‐P (∼54 × 10−3 Vm/N) samples over the KBT‐C ceramic was obtained. Interestingly, a significantly lower activation energy (Ea) for KBT‐C (∼0.71 eV) below the temperature of the dielectric maximum (Tm) was noticed compared to KBT‐R (∼1.07 eV) and KBT‐P (∼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.