Synthesis and dielectric properties of layered-perovskite KCa2Nan-3NbnO3n+1 ceramics

KCa2NaNb4O13 (4KCNNO)1 ceramics are well-sintered at 1325 °C without any secondary phase. However, K2O evaporation occurs in KCa2Na2Nb5O16 (5KCNNO)2 ceramics calcined at temperatures higher than 1200 °C, resulting in the formation of the KCa2Na3Nb6O19 (6KCNNO)3 secondary phase. Excess-K2O was added to the 5KCNNO specimen to synthesize pure 5KCNNO ceramics by compensating for the evaporated K2O. The 5KCNNO ceramic containing 20 mol% excess-K2O sintered well at 1325 °C without any secondary phase. However, the 6KCNNO secondary phase also developed in specimens containing a large excess of K2O, owing to the reaction between excess-K2O and the 5KCNNO phase. Dielectric constant (ɛr) of the 4KCNNO ceramic is 62 with a dielectric loss (tan δ) of 0.6% at 100 kHz and the 5KCNNO ceramic showed increased ɛr of 70 with tan δ of 0.3% at 100 kHz. The increase in the ɛr value is rationalized by the increased number of NbO6 octahedral layers between the K+ layers. In addition, the structural and dielectric properties of the 5KCNNO ceramic are more important than those of the 4KCNNO ceramic from the application point of view, because the εr value of the 5KCNNO ceramic is larger than that of the 4KCNNO ceramic.