Besides the higher sintering density, another probable reason for the reduction of evaporation is the formation of K4Nb6O17 phase for CSAS samples. As mentioned before, the K-rich amorphous precipitates will transform into K4Nb6O17 second phase during sintering procedure, because the formation of K4Nb6O17 phase is greatly related to the added water in the cold sintering process. The coverage of K4Nb6O17 on the grain surface of KNN would help to restrict the evaporation of alkali elements due to the higher melting point of K4Nb6O17 (1177oC) than KNN (~1110oC).[36] In this sense, the increase of sintering density and the formation of K4Nb6O17 coverage can greatly suppress the evaporation of alkali elements during the final stage of sintering, and result in compositional uniformity and accurate stoichiometry, which would have positive effects on the electrical properties of KNN ceramics.
Besides the higher sintering density, another probable reason for the reduction of evaporation is the formation of K4Nb6O17 phase for CSAS samples. As mentioned before, the K-rich amorphous precipitates will transform into K4Nb6O17 second phase during sintering procedure, because the formation of K4Nb6O17 phase is greatly related to the added water in the cold sintering process. The coverage of K4Nb6O17 on the grain surface of KNN would help to restrict the evaporation of alkali elements due to the higher melting point of K4Nb6O17 (1177oC) than KNN (~1110oC).[36] In this sense, the increase of sintering density and the formation of K4Nb6O17 coverage can greatly suppress the evaporation of alkali elements during the final stage of sintering, and result in compositional uniformity and accurate stoichiometry, which would have positive effects on the electrical properties of KNN ceramics.
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