Correlation between hopping conduction and transferred exchange interaction in La 2NiO 4+ δ below 300 K

Abstract

In order to investigate the correlation between electrical transport properties and the transferred exchange interaction between Ni 2+ and La 3+ in La 2NiO 4+ δ , bulk conductivities and dielectric properties of La 2NiO 4.02 and La 2NiO 4.125 have been measured as a function of temperature up to 300 K. The complex-plane impedance analyses determined bulk conductivities. Temperature dependencies of bulk conductivities, the self-consistent agreement of the energies obtained in the bulk conduction and dielectric relaxation processes, and the electron transferred integrals determined in dielectric measurements are indicative of the nonadiabatic hopping conduction, although the conductivity in La 2NiO 4.125 is very high with a very low hopping energy in comparison with La 2NiO 4.02. These results have been discussed in terms of the transferred exchange interaction between Ni 2+3d z 2 orbital and La 3+6s orbital through 2p z orbital of apical O 2−. With increasing the content of excess oxygen, the decrease in the number of Ni 2+3d z 2 orbitals, which play an important role in the transferred exchange interaction, changes remarkably the conduction behaviour in La 2NiO 4.125 from La 2NiO 4.02.