An ac conductivity as well as dielectric relaxation property of La2NiO4.1 is reported in the temperature range of 77？K–130？K and in the frequency range of 20？Hz–1？MHz. Complex impedance plane plots show that the relaxation (conduction) mechanism in this material is purely a bulk effect arising from the semiconductive grain. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with the activation energy of ~0.09？eV. The frequency-dependent electrical data are also analyzed in the frame of ac conductivity formalism. The ac conductivity has been found to follow a power-law behavior at a limited temperature and frequency region where Anderson localization plays a significant role in the transport mechanism for La2NiO4.1. 1. Introduction Perovskite oxides with high dielectric constant play an important role in microelectronics [1] and have been used as memory devices and capacitors. In the literature, the dielectric relaxation with extremely high permittivity has been reported in many materials, in which the contribution of conduction carriers to dielectric polarization may play an important role. However, the explanation of this phenomenon is controversial based on different models [2, 3]. The electron localized on an ion can cause displacements of neighboring ions from their positions in the crystal lattice. The quasi-particle formed by an electron and corresponding lattice displacements is called polaron [4, 5]. Crystal chemical considerations indicate that among the ternary transition metal oxides of the type A2BO4, only La2NiO4 should be stable in the K2NiF4 structure [6–8]. The natures and properties of La2NiO4 are highly sensitive to the content of excess oxygen. In fact, La2NiO4+δ exhibits the metal-insulator transition [8]. Although La2NiO4+δ remains semiconducting nature up to , hole doping due to excess oxygen induces increasing structural distortion and changes electronic structures which modify the band gap width [9]. La2NiO4+δ exhibits semiconducting behavior at low temperatures with thermally activated or variable range hopping-type conductivity [10, 11]. The previous experimental results suggest a high possibility that the major carrier at low temperature in La2NiO4+δ is a polaron [10, 11]. However, the details of the transport kinetics are still unknown. Although there are many ways of
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