Annealing effect on surface morphology and electrical transport of PbPdO2 and Pb(Pd,Co)O2

We have studied the ex-situ annealing effects on the surface morphology and electrical transport of gapless semiconductors, PbPdO2 and Pb(Pd,Co)O2 thin films, with varying annealing temperature and time. The annealing process gives rise to better surface morphology in both samples. The optimal annealing conditions are obtained to be 650  °C and 12 h. On the other hand, the electrical properties are differently found for both samples. The electrical conduction is improved for PbPdO2 film by annealing, while it is lowered for Pb(Pd,Co)O2 film. The improvement of electrical conduction for PbPdO2 is well explained by the reduction of lattice imperfections of PdO droplets and Pd or O deficiencies, which is related with the hybridization between the Pd 4d and O 2p bands. However, this tendency is not applied for Pb(Pd,Co)O2 because of the trivalent Co state, which generates the monovalent Pd state, leading to the decrease of electrical conduction as a result of the reduction of Pd(4d)-O(2p) hybridization.