Reactive templated grain growth and anisotropic electrical properties of (Na0.5K0.5)NbO3 ceramics without sintering aids

Abstract

(Na0.5K0.5)NbO3 (KNN) ceramics with {100} orientation without sintering aids were fabricated by a conventional process and reactive templated grain growth using tabular NaNbO3 template particles. The KNN specimen sintered at 1,170 °C for 15 h were found to have a relative density of 95.6%. The experimental results show that the textured ceramics have a pseudo-cubic {100} orientation degree of 96.2% and a microstructure with brick-like grains aligning in the direction parallel to the casting plane. The dielectric constant is much higher than the value for non-textured ceramics. Transition temperatures (T o–t, T c) are reduced and dielectric peaks are greater breadth. Remanent polarization P r decreased from 19.40 (the random KNN) to 13.77 (textured KNN) μC/cm2. The textured ceramics show anisotropic electrical properties between different directions of textured KNN ceramics, and show a very high electromechanical coupling factor k p = 0.58 and a high piezoelectric constant d 33 = 225 pC/N, compared to the random counterparts (k p = 0.31, d 33 = 115 pC/N).