Influence of donor and acceptor doping on conductivity in potassium niobate

Lead-free ferroelectrics based on the (K,Na)NbO3 solid solution have emerged as strong candidates to replace lead-containing ceramics due to their excellent piezoelectric and thermal properties. However, their practical application is hindered by high leakage currents and low ceramic density. Doping provides a strategy for enhancing material performance, highlighting the need for a deeper understanding of defect chemistry. For this purpose, we investigated the equilibrium of intrinsic defects and the doping behaviour of Ca and Fe in the boundary phase KNbO3. We found all elements to be prone to vacancy formation. Moreover, Ca acts as a donor and leads to a large concentration of charge carriers and therefore larger electronic conductivity. On the other hand, Fe behaves as an acceptor and shows oxidation states ranging from 2+ to 5+, whose concentrations depend on the total Fe concentration. As a consequence, the number of charge carriers and the electronic conductivity are reduced.