The influence of different niobium pentoxide precursors on the solid-state synthesis of potassium sodium niobate

Two batches of K0.5Na0.5NbO3 were prepared from the orthorhombic and monoclinic Nb2O5 polymorphs and potassium and sodium carbonates. The influence of the different Nb2O5 precursors on the solid-state synthesis of K0.5Na0.5NbO3 was studied. To reduce the particle size, both types of Nb2O5 were milled prior to use. XRD and TEM analyses showed that the milled orthorhombic Nb2O5 was single phase; however, after milling the monoclinic Nb2O5 consisted of large monoclinic particles and orthorhombic nanocrystals. The latter reacted with the carbonates to form (KxNa1-x)NbO3 solid solutions with varying K/Na molar ratios, while the orthorhombic Nb2O5 reacted to form a homogeneous solid solution of K0.5Na0.5NbO3. Sintering of the two powder compacts resulted in different densification behavior and microstructure. This study shows the important influence of the Nb2O5 precursor phase and the particle size distribution on the homogeneity and further densification of the potassium sodium niobate solid solution.