Research On The Dielectric Properties Of La_2-xSr_xNiO_4-δ

Solid dielectric material is the one that transfer electromagnetic signals by induced polarization and it plays an important role in scientific research and practical applications. Not only it can be used as insulator but also used to make of capacitors, piezoelectric device and so on. Dielectric constant is one of important parameters reflecting the dielectric properties. To miniaturization of electronic components, high precision, high stability and high energy reservoir with the continuous progresses of information society, researchers are forced to explore new solid dielectric materials having high dielectric constants and low losses.At present, the high dielectric materials were mainly some perovskite materials and transition metal oxides. In this thesis, we have synthesized La_2-xSr_xNiO_4-δ(x=1/2,x=1/3)materials with high dielectric constant. From XRD results, the samples are good single-phase. Temperature dependant impedance spectra were measured to study the polarization of the samples. Further, in order to explore the mechanisms of the high dielectric constant, we also investigated the annealing effects with 600℃and 800℃at high vacuum 7×10-4 Pa.From the analysis, La_2-xSr_xNiO_4-δ(x=1/2,x=1/3)materials have high dielectric constant. At the same time we find the dielectric constant of x=1/2 was larger than x=1/3, indicating that the performance of x=1/2 was much better than x=1/3. The dielectric constant of the sample with x=1/2 is about 105 at room temperature. But it has leakage current losses and so inhibits its application. From the research and analysis, we proposed that the high dielectric constant may originate from grain boundaries and grains. The dielectric constant decreases after vacuum annealing with the reason that some Ni³⁺ transformed to Ni²⁺ since the decrease of oxygen content. The above investigations indicate that the high dielectric constant would be correlated with the arrangement of Ni³⁺ and Ni²⁺.