Dielectric behavior of KNN-SrTiO3 ceramics in solid solution and composite states

초록

This study investigates the dielectric behavior of 80(K0.5Na0.5)NbO3-20SrTiO3 (KNN-ST) ceramics with distinct phase constitutions, prepared as a solid-solution system (KNN-ST_1) and a physically mixed composite system (KNN-ST_2). X-ray diffraction analysis indicated the formation of a predominantly pseudo-cubic phase in KNN-ST_1, whereas KNN-ST_2 retained coexisting KNN- and SrTiO3-related phases. Microstructural observations revealed distinct differences in grain morphology and phase distribution, with KNN-ST_1 exhibiting relatively uniform faceted grains and KNN-ST_2 showing heterogeneous phase-separated microstructures. Dielectric measurements demonstrated that both systems exhibited frequency-dependent dielectric behavior and more stable dielectric responses over the measured temperature range than pure KNN, whereas KNN-ST_1 showed higher permittivity and lower dielectric loss than KNN-ST_2 over the measured frequency range. These differences are discussed in relation to distinct phase constitutions, interfacial configuration, grain growth behavior, and residual porosity associated with the respective synthesis approaches. The results provide comparative insight into how phase constitution and microstructural heterogeneity are associated with the dielectric response of KNN-based lead-free ceramic systems.

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