Giant Dielectric Responses In Ln_5/3Sr_1/3NiO₄-Based Ceramics

Since the discovery of CaCu3Ti4O12, materials with giant dielectric response have gained great considerable scientific attentions, and series of theoretical analysis have been proposed to explain that phenomenon. Several kinds of theories were built for ceramics with K2NiF4structures, and they mainly divided into two categories, intrinsic effects and extrinsic effects. Among these theories, the small polaronic hopping model is highlight. In this thesis, the structures and dielectric properties were investigated systematically. The relationship between dielectric properties and structures was discussed deeply, and the origin of the giant dielectric effect was revealed.The structures of La5/3Sri1/3NiO4+δ and Nd5/3Sr1/3NiO4+δ ceramics obtained by sol-gel method were characterized by X-ray diffraction at room temperature, and single tetragonal phases were found in the ceramics. Giant dielectric effect was found in both of the ceramics, and a dielectric relaxation was observed in low temperature (140K). The concentration of oxygen vacancies increased and the dielectric properties changed after post-annealing in a flow of nitrogen. The dielectric behavior of ceramics confirmed the correlation between the dielectric response and oxygen vacancies. After comparing the activation energies of dielectric relaxations and electrical conductivities, the giant dielectric response should be attributed to the adiabatic small polaronic hopping process.The structures of La5/3Sr1/3Ni1-xAlxO4and Nd5/3Sr1/3Ni1-xAlxO4ceramics (x=0.2,0.3) have been investigated through X-ray diffraction. Temperature stable giant dielectric response was observed in all the ceramics. The dielectric permittivity decreased while the loss increased with increasing the amount of Al3+ions. After analyzing the dielectric relaxation behavior and activation energy, the giant dielectric response should be attributed to the adiabatic small polaronic hopping process. Based on the experimental data of ceramics with various x, the relationship between dielectric relaxation and polaronic hopping was confirmed...