The electronic properties of perovskite-type oxides ABO(3) can be characterized by the degree of localization of d-electrons. On the other hand, the complex perovskite oxides A(1-x)A(x)'B1-yBy'O3-delta exhibit ionic conduction through the defects created by partial substitution of metal atom A and (or) B. In the present study, the relationship between the ionic conduction and the nature of electronic transport properties in perovskite-type oxides is discussed by extending the classification scheme of localized and itinerant d-electron diagram used for ABO3 compounds. The classification scheme is based on the potential parameter Z/r, where Z and r are the valence and ionic radii of the cation. From the analysis, it is found that in perovskite oxides, the oxygen ionic conductivity decreases with Z(A)/r(A) of ion A. The result indicates that the nature of the electronic state influences the ionic conduction. An interpretation of the result found in terms of the bond fluctuation model of superionic conductors is given. (C) 2012 Elsevier B.V. All rights reserved.

The heat of transport determined from the thermopower measurement provides important information to know the ion transport processes occurring in solid electrolytes. Recently, we have proposed a theoretical model for the heat of transport in ionic conductors. According to the model, the relationship between the heat of transport and the activation energy of ion conduction is determined by the participation degree of different phonon modes. In the present study, some behavior expected from the model is compared with experimental observations. It is shown that the predictions of the model are consistent with the experimental data.

In complex perovskite oxides, it has been reported that the thermal expansion coefficient increases with the increase in the oxygen ionic conductivity. However, its theoretical background has not been clarified yet. In the present study, a model to understand the relationship is presented. By analyzing the experimental data using the theoretical expression derived, microscopic quantities related to ionic transport has been obtained.

In complex perovskite-type oxides, which have been studied as cathode materials, the thermal expansion coefficient (TEC) increases with the increase in the oxygen ionic conductivity. The aim of the present study is to explain such a behavior from a chemical bond point of view. For the perovskite oxides expressed as A1-x A′ x B1-y B′ y O3-δ and ABO3, the ionicity of A‒O and B‒O bonds and the thermal expansion coefficient were evaluated theoretically by using semiempirical methods. It is found that the thermal expansion coefficient and the oxygen ionic conductivity decrease with the increase in the difference of the ionicity between A‒O and B‒O bonds.

The electronic properties of transition metal oxides ABO3 can be characterized by the degree of localization of d-electrons. On the other hand, the complex oxides A1-xA'x B1-yB'yO3-δ with perovskite structure exhibit high ionic conduction. Is there any relation between the nature of electron localization and the ionic conduction? In the present paper, a preliminary study to answer this question is presented. It is shown that the ionic conductivity correlates with the quantity ZA/rA, where ZA and rA are the effective valence and radius of the cation A. It is also shown that for compounds with rhombohedral structure, the magnitudes of the ionic and electronic conductivities are correlated.

In complex perovskite-type oxides which have been studied as cathode materials, the thermal expansion coefficient increases with the increase in the oxygen ionic conductivity. In the present study, with the aim to explain such a behavior, a research has been carried out from a chemical bond point of view. For oxides A1-xA′xB1-yB′yO with perovskite structure, the ionicity of the individual bond, A-O and B-O, and the thermal expansion coefficient of mixed compounds were estimated by using semiempirical methods. It has been shown that the thermal expansion coefficient and the oxygen ionic conductivity decrease with the increase in the difference of the ionicity between A-O and B-O bonds. It is also found that the tolerance factor and the specific free volume are linearly correlated with the difference of ionicity.

The ion flow caused by a temperature gradient originates the ionic thermopower which is quantified by the heat of transport. Experimentally, it is known that in superionic conductors, the heat of transport Q is nearly equal to the activation energy for ion transport Ea. In the present paper, a model for the heat of transport in ionic conductors has been proposed based on a lattice dynamical theory of diffusion. We have shown that the relationship between Q and Ea is determined by the participation degree of different phonon modes, in particular the short wavelength phonons to the atomic jump processes. The implication of this finding to the transport properties of superionic conductors has been discussed, and it is suggested that the degree of the collective motion in ionic conductors increases with the increase in Q/Ea. The model predicts that good ionic conductors will show large value of Q/Ea. The importance of the acoustic phonons in the ion transport processes has been also pointed out.