Insights into the correlation between ionic characteristics and microstructure and multiferroic properties in KNN-based ceramics with BiMO3 modification

Abstract

As one of the most promising eco-friendly piezoelectric materials, potassium sodium niobate (KNN)-based ceramics prepared via a phase engineering strategy have recently received considerable attention. Surprisingly, the different piezoelectric properties can also be obtained in KNN-based ceramics even with the same phase coexistence, illustrating that the mechanisms of improved properties have not been sufficiently addressed apart from phase coexistence, especially the role of the characteristics of individual elements in the modification of structure and performance. Herein, a group of BiMO3-doped KNN-based ceramics was designed to probe the qualitative correlation between ionic characteristics (ionic radius and electronegativity) and structure as well as multiferroic properties. Due to the different efficiency of ion on shifting phase transition temperatures, the R-T phase boundary with varying R and T phase fractions is displayed in BM ceramics, while the evolution of relaxor behaviour is ascribed to the decreased grain size resulting from the enhanced ionic radii of Ga3+, Fe3+, and Sc3+. Owing to the distinction in the covalence fraction caused by the electronegativity, d33 first increased and then decreased from BG to BF to BS ceramics. The superimposed effect of the T-phase fraction, c/a ratio, and covalence fraction dominates the evolution of the temperature-dependent normalised electric properties. Additionally, higher magnetic properties are beneficial for the super-exchange interactions occurring with the –Fe–O–Nb–O–Fe– pathways in BF ceramics. Therefore, exploring the role of characteristics for individual elements in the structure and performance is helpful for sufficiently understand the doping mechanism.