Mechanochemical reaction in the K2CO3–Nb2O5 system

We studied the mechanochemical synthesis of KNbO3, starting from a powder mixture of K2CO3 and Nb2O5. The milling experiments were designed with different ball-impact energies in order to investigate the mechanochemical reactions. X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, Raman spectroscopy and transmission electron microscopy were used to characterize the samples. Based on the results, we propose a mechanism for the mechanochemical reaction between K2CO3 and Nb2O5. The first stage of the reaction is characterized by the formation of an amorphous carbonato complex, which decomposes after prolonged milling at higher ball-impact energy giving rise to the crystallization of KNbO3 and other niobate phases with a molar ratio K/Nb < 1. The reaction course is discussed and compared with the Na2CO3–Nb2O5 system.