The rare-earth dependence on the solid solution formation and electrical properties of KCa_2-xR_xNb₃O₁₀ (R=Nd, Sm, Gd and Ce)

The solid solution KCa_2-xR_xNb₃O₁₀ (R=Nd, Sm, Gd and Ce) was prepared by solid-state reaction using KCa₂ Nb₃O₁₀, KNbO₃, Nb₂O₅, Nb and rare-earth oxides. The solubility limit of the solid solutions was extended with an increase in the ionic radii of the rare earths. All the solid solutions exhibited similar semiconductive behavior with a linear log p-T relationship over a wide temperature range. These results suggest that the conduction mechanism is independent of the type of rare earths and also the unit-cell parameters, which agrees well with the tunneling conduction model with a vibrating barrier.