【作者】 俞超；

【导师】 吴勇军；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2012， 硕士

【摘要】 作为一类应用广泛的微波磁性材料和磁光材料,稀土铁石榴石的各种磁性能及磁光特性已经被广泛地研究。近年来,随着多铁性研究的兴起,其介电性能和磁介电性能也越来越受到关注。本论文研究了一系列离子部分置换的稀土铁石榴石陶瓷的结构与相变,分析了其宽温宽频范围内的介电弛豫现象,探讨了离子置换对其磁介电效应的影响规律。Y3Fe5.xAl,O12(x=0,0.5,1,2,3)陶瓷中,Al3+离子优先占据四面体空隙。其在测试温度(133-573 K)和频率(10 Hz-1 MHz)范围内均观察到了巨介电效应。随着Al置换量的增加,Fe2+-Fe3+之间的电荷跃迁所对应的低温介电弛豫的激活能增加。其饱和磁化强度和磁有序温度也随着Al置换量的增加而逐渐降低。Bi置换降低了Y3-χBiχFe5O12(x=0,0.5,1)陶瓷的介电常数与介电损耗,使其饱和磁化强度降低,磁有序温度升高。且随着Bi置换量的增加,非本征因素(Maxwell-Wagner效应和磁阻效应等)和本征因素(Fe2+-Fe3+偶极子的重新排列和磁致伸缩效应等)对磁介电效应的贡献都降低,共同导致了陶瓷磁介电效应的减弱。Ti置换使Y3Fe5-χTixO12+x/2(x=0,0.1,0.2)陶瓷在低温区除了与Fe2+-Fe3+之间的电荷跃迁相关的介电弛豫外,还出现了一个与Ti3+-Ti4+之间的电荷跃迁相关的介电弛豫,且弱化了与Maxwell-Wagner效应相关的中温介电弛豫。随着Ti置换量的增加,非本征效应对磁介电效应的贡献降低,本征效应对磁介电效应的贡献增强,使其磁介电系数随着置换量的增加先减小后增加。在Ln3Fe5O12(Ln=Sm, Y, Yb)陶瓷中,随着稀土离子半径的减小,Fe-O-Fe结构更加松散,自身的耦合作用减弱,对外加磁场的响应增强,导致磁介电效应的增强。更多还原

【Abstract】 Rare earth iron garnet (RIG), a ferrimagnetic material known as microwave ferrite, has been widely applied in passive microwave devices and magneto-optical devices. Its magetic and magneto-optical properties have been widely investigated. Recently, the investigations of dielectric properties and magnetodielectric effects in RIG have been attracting much interest. In this work, structure, dielectric response, magnetic properties and magnetodielectric properties of rare earth iron garnet ceramics were investigated.In Y3Fe5.χAlχ-O12(x=0,0.5,1,2,3) ceramics, Rietveld refinement of XRD data suggests that Al3+substitutes for Fe3+at tetrahedral sites. All the samples show a giant dielectric response which originates from the charge carrier hopping between the Fe2+ and Fe3+. The activation energy of the hopping process increases with increasing Al substitution. The a-d super-exchange interaction becomes weak as the content of Al increases, which results in the decrease of saturation magnetizations and magnetic ordering temperatures.It was found that the dielectric constant and dielectric loss of Y3.rBiχFe5O12(χ=0, 0.5,1) ceramics decrease with increasing Bi amount. The saturation magnetization decreases and the magnetic ordering temperature increases as the amount of Bi increases. The contribution of the intrinsic and extrinsic effects to magnetodielectric effects decreases with increase of Bi, which results in the decrease of magnetodielectric coefficient of Y3-χBiχFe5O12ceramics.Ti substitution induces a low temperature dielectric relaxation which comes from the charge carrier hopping between Ti3+and Ti4+for Y3Fe5-χTiχO12+χ/2(χ=0,0.1,0.2) ceramics. The Maxwell-Wagner effect related dielectric relaxation becomes weak as the content of Ti increases. The contribution of the extrinsic effects to MD effect decreases and the contribution of the intrinsic effects to MD effect increases with increasing Ti amount, so the magnetodielectric coefficient first decreases and then increases.The coupling becomes weak with ionic radius decreases for Ln3Fe5Oi2(Ln=Sm, Y. Yb) ceramics, which enhances the response when magnetic field is applied. As a result, the magnetodielectric effect increases.更多还原