Insulator–metal transition induced in Sr1−xNaxPd3O4 for small Na-substitutions

The electric and magnetic properties of Sr1−xNaxPd3O4 (0≤x≤0.2) were studied using polycrystalline specimens. The electrical conductivity increases following the substitution of Na, and an insulator–metal transition was observed for very small Na contents between 0.075 and 0.1. The results of Hall-effect measurements indicate that holes are introduced depending on the Na contents. Paramagnetic behavior with an increase of the susceptibility at low temperature was observed for all specimens. No abrupt shrinking of the lattice was observed near the insulator–metal transition. The insulator–metal transition seems to arise not in the form of a Mott transition but by a process in which Na-substitution directly introduces mobile carriers into the valence band, establishing a metallic state for specimens with x>0.75. This must be due to the semimetallic character of the electronic band structure of SrPd3O4.