Microstructure and microchemistry of flash sintered K0.5Na0.5NbO3

Flash sintering experiments were performed, for the first time, on sodium potassium niobate (KNN) ceramics. A theoretical density of 94% was achieved in 30 s under 250 V/cm electric-field at 990 degrees C. These conditions are similar to 100 degrees C lower and faster than the conventional sintering conditions. Grains tended to grow after 30 s. flash sintering duration under constant electric-field. Detailed microstructural and chemical investigations of the sample showed that there was inhomogenous Na, K distribution and it resembles a core-shell structure where K is more in the shell and Na is more in the core region. The inhomogenous distribution of Na and K was correlated with the doubling of the unit cell within the grain along 002 direction. Compositional equilibrium is achieved after a heat treatment at 1000 degrees C for 4 h. The compositional variations appeared to have been linked to grain boundary melting during flash and consequent recrystallization as the sample cooled. (C) 2016 The Ceramic Society of Japan. All rights reserved.