Synthesis of size controlled phase pure KNbO3 fine particles via a solid-state route from a core–shell structured precursor

From a core–shell structured precursor, comprising Nb2O5 core enveloped by KHCO3 in an equimolar proportion, phase pure KNbO3 (KN) fine particles were obtained by calcining in air at 600 °C for 1 h. Disintegrating the large agglomerated particles of KHCO3 prior to the precursor preparation enabled the micronization of the KN particle size down to 240 nm, close to that of the starting Nb2O5, due to increased mixing homogeneity and consequent thorough enveloping of individual Nb2O5 particles. Based on these findings, together with the known coupling diffusion mechanism of potassium and oxygen into Nb2O5, it was concluded that the core–shell particles in the precursor serve as a separated reaction space to complete the formation of KN without appreciable coalescence or local sintering, as far as the firing temperature is low enough like those employed in the present study. Superiority of KHCO3 over K2CO3 or KNO3 as a potassium source was also discussed.