Correlation between hopping conduction and transferred exchange interaction in La2NiO4+delta below 300 K

In order to investigate the correlation between electrical transport proper ties and the transferred exchange interaction between Ni2+ and La3+ in La2N iO4+delta, bulk conductivities and dielectric properties of La2NiO4.02, and La2NiO4.125 have been measured as a function of temperature up to 300 It. The complex-plane impedance analyses determined bulk conductivities. Temper ature dependencies of bulk conductivities, the self-consistent agreement of the energies obtained in the bulk conduction and dielectric relaxation pro cesses, and the electron transferred integrals determined in dielectric mea surements are indicative of the nonadiabatic hopping conduction, although t he conductivity in La2NiO4.125 is very high with a very low hopping energy in comparison with La2NiO4.02. These results have been discussed in terms o f the transferred exchange interaction between Ni(2+)3d(z2) orbital and La( 3+)6s orbital through 2p(z) orbital of apical O2-. With increasing the cont ent of excess oxygen, the decrease in the number of Ni(2+)3d(z2) orbitals, which play an important role in the transferred exchange interaction, chang es remarkably the conduction behaviour in La2NiO4.125 from La2NiO4.02. (C) 1999 Elsevier Science B.V. All rights reserved.