Study On Giant Dielectric Effect Of Garnet Ferrite Re₃Fe₅O₁₂（Re=Er,Yb,Lu）

With the rapid development of electronic information technology,multifunctional materials have attracted great attention from researchers.Generally,the physical phenomenon of high dielectric constant（ε’>10³）in materials is called the giant dielectric effect.The giant dielectric effect has potential and broad application prospects for the miniaturization of electronic devices such as memory devices,oscillators,waveguide optical isolators and phase shifters.As one of the basic multifunctional materials,rare earth garnet type ferrite(Re₃Fe₅O₁₂)ceramic materials often exhibit the giant dielectric effect in a certain temperature and frequency range.Therefore,this dissertation selects garnet-type ferrite as the research object,and conducts systematic research around finding new types of giant dielectric materials and exploring the causes of giant dielectric effects.The main research results are as follows:（1）The polycrystalline Er₃Fe₅O₁₂ ceramic sample was synthesized by using the solid-phase reaction method.The change curve of dielectric constant with frequency and temperature shows that the sample exhibits a giant dielectric effect in a wide range of temperature and frequency.The results of dielectric-relaxation analysis show that the relaxation in the relatively low temperature range is mainly due to the transition of carriers between Fe²⁺and Fe³⁺,and the dielectric relaxation in the higher temperature range may be mainly related to the oxygen vacancies inside the material.The defect is related.The analysis of the experimental results shows that the giant dielectric effect may originate from the accumulation of carriers at the grain boundaries.（2）The Yb₃Fe₅O₁₂ polycrystalline ceramic sample prepared by the solid-phase reaction method has a giant dielectric effect in a wide temperature and frequency range.The dielectric-relaxation analysis results show that the relaxation in the lower temperature range may be derived from the transition of carriers between Fe²⁺and Fe³⁺;the relaxation in the higher temperature range may be mainly affected by double ion oxygen vacancies.The analysis result of impedance spectroscopy shows that when the temperature is low,the crystal grains have a significant influence on the dielectric relaxation,and when the temperature is high,the crystal grains and the grain boundaries both have a certain influence on the dielectric relaxation.A comprehensive analysis of the experimental results shows that the giant dielectric effect of the sample may be caused by the accumulation of carriers at the grain boundaries.（3）Lu₃Fe₅O₁₂ ceramic samples were synthesized by a solid-phase method.The dielectric measurement results of the samples showed that the Lu₃Fe₅O₁₂ ceramic samples exhibited giant dielectric effects above room temperature（300 K）and a wide frequency range（100 Hz～1 MHz）.The dielectric relaxation analysis results show that the dielectric relaxation in the lower temperature range is mainly related to the transition of carriers between Fe²⁺and Fe³⁺,and the dielectric relaxation in the higher temperature range may be related to the double ion oxygen vacancy and conductivity is related.The impedance spectroscopy-measurement results show that when the grains and grain boundaries contribute to the dielectric relaxation,the influence of the grain boundaries is significant when the frequency is lower,and the influence of the grains is more obvious when the frequency is higher.It is particularly important to note that as the temperature increases,more and more carriers will accumulate at the grain boundaries at lower frequencies.This may be the reason of the giant dielectric effect in the sample.