Solid-State Reaction Mechanism and Deliquescence Phenomenon of K_0.5Na_0.5Nb_0.7Al_0.3O₃ Ceramic

Development of (K,Na)NbO₃-based ceramics has attracted much attention in recent decades. In this work, K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K₂CO₃, Na₂CO₃, and Nb₂O₅ as well as K₂CO₃, Na₂CO₃, and Al₂O₃, which can influence the sintering behavior of the mixture. (K,Na)NbO₃ and (K,Na)AlO₂ were present in the sintered K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic, with the latter leading to deliquescence. During the sintering process, Al₂O₃ reacts with alkali oxides (Na₂O and K₂O), which are the decomposition products of carbonates, to form (K,Na)AlO₂. In addition, Al₂O₃ is more likely to react with K₂O compared with Na₂O.