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°C.These conditions are ³100°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 coreshell 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°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.