Effect of Mo substitution on the structure and electrical properties of Gd2Ru2O7 pyrochlore

Abstract

Polycrystalline samples of Gd2Ru2-xMoxO7 were prepared by the molten salt method. Rietveld refinement showed that a lattice parameter increases as the Mo content increases. Bond-valence sum model analysis (BVS) shows high stability in the structure. An increase in XPS valence band (VB) intensity at zero eV is observed as the Mo content increases. Theoretical calculations within the local density approximation, considering Hubbard U, reveal that the Gd2Ru2O7 compound is a semiconductor with activation energy (Ea) of 0.089 eV. DOS analysis shows that the main contributions are the Ru4d and O 2p states. Good correspondence is observed between the VB measure and the DOS calculated. Electrical resistivity measurements at low temperatures show that the Gd2Ru2O7 compound is a semiconductor with an Ea of 0.098 eV and decreases with Mo content. We suggest two conduction mechanisms; ionic conduction occurs via oxygen vacancy or interstitial migration and electronic conduction via variable-range hopping.