Study of the ionic conductivity in Ce$_{1/3}$NbO$_{3}$

Ce$_{1/3}$NbO$_{3}$was synthesized using stoichiometric quantities of CeO$_{2}$ and Nb$_{2}$O$_{5}$ and heated for 48h at 1350$^{o}$C in air. The electric conductivity was measured in the 25$^{o}$C-1000$^{o}$C interval. A small gap of 0.25-0.78eV was found. To study the origin of the transport DFT calculations were carried out; the results show a 0.4eV gap, but since the gaps are not correctly predicted with DFT, a further calculation with a modified Becke-Johnson (mBJ) potential was carried out obtaining a gap of 2eV, but a Ce 4f peak was found at the Fermi energy (E$_{F})$. When an intra-atomic repulsion term was added (LDA+U) the Ce 4f peak moved down and a 2.4eV gap was found. The calculations show that the conductivity does not have electronic origin but ionic. Atomistic calculations rule out that the transport is due to the Ce ions; on the other hand, these calculations agree very well with oxygen ions as charge carriers in this material.