Revisiting the Role of Nb ₂ O ₅ Precursors on Solid‐State Formation Reactions of (K 0.5 Na 0.5 )NbO ₃

ABSTRACT (K 0.5 Na 0.5 )NbO 3 (KNN) is a key lead‐free piezoelectric material, yet reproducibility is limited by microstructural and chemical inhomogeneity. We systematically examined how the crystal structure and the particle size distribution of Nb 2 O 5 control KNN formation. Specifically, we studied four Nb 2 O 5 precursors: orthorhombic and monoclinic phases, each prepared with homogeneous and inhomogeneous particle size distributions. The results indicate that the KNN formation pathway depends on the crystal structure of the precursor. Whether a single perovskite KNN phase forms, or KNN coexists with KNbO 3 and NaNbO 3 , is governed mainly by the crystal structure of Nb 2 O 5 precursors and is largely independent of particle size distribution. Diffusion is the dominant driving force, while its effectiveness varies with the precursor through differences in structural stability and transformation behavior. These findings emphasize that careful selection of the Nb 2 O 5 precursor is essential for reproducible and chemically homogeneous KNN ceramics.