Fe基单相室温多铁陶瓷的结构与性能

发布时间：2018-05-03 00:46

本文选题：BiFeO_3 + 六角稀土铁氧体　；参考：《浙江大学》2017年博士论文

【摘要】：近年来,多铁性材料由于其丰富的物理内涵和广阔的应用前景,得到了越来越广泛的关注与研究。本论文以BiFeO3和h-LuFeO3两类Fe基单相多铁材料为研究对象,系统研究了其制备、结构与性能调控,获得如下主要结论。通过与Sr0.5Ca0.5TiO3形成固溶体,BiFeO3基陶瓷的结构逐渐由菱方变为正交结构。该固溶体的形成显著降低了 BiFeO3陶瓷的电导率,x=0.25及0.3两组分的铁电性能得到明显的改善。铁电性能的改善可归因于漏电流密度的降低。最佳磁性能在=0.25时得到,剩余磁化强度高达Mr=34.8emu/mol。磁性能的增强主要归因于Ti4+离子置换Fe3+离子,破坏了空间调制的螺旋自旋磁结构。Sr/Ca比对BiFeO3-(Sr,Ca)TiO3陶瓷的结构与性能有显著的影响。随着Sr/Ca比的增大,菱方-正交相界逐渐向(Sr,Ca)TiO3一端移动。最佳铁电性能出现在相界附近富菱方相。磁性能主要受B位置换的影响,在B位置换量为20%～25%时得到最佳磁性能。在(1-x)BiFeO3-x(0.5CaTiO3-0.5SmFeO3)三元系陶瓷中,随x的增加,陶瓷结构逐渐由菱方的R3c(x≤0.2)变为正交Pbnm(x≥0.3),且有少量中间相出现。在很宽的一个成分范围内极性R3c与非极性Pbnm两相共存,且两相的含量随x的变化而改变。介电及DSC分析结果表明,在x≤0.2的组分中存在明显的热滞,这说明主相为R3c的成分是典型的弥散铁电体,具有一级铁电相变的特征。随着x的进一步增加,介电常数出现明显的频率色散,且存在两个介电弛豫过程。高温介电弛豫与晶界相关,低温介电弛豫与Fe2+和Fe3+之间的电荷转移相关。铁电性能在x≤0.2的几个成分内得到了明显的增强,这与其内部的极性相R3c相关。同时,磁性能测试表明,磁性能得到了显著的改善,室温下最佳磁性能Mr=63.2emu/mol。磁性能的增强主要归因于Ti离子的置换破坏Fe-O-Fe超交换作用。此外,磁性稀土 Sm离子的置换是低温磁性能显著改善的主要原因。在LuFe03中通过In离子置换,获得了稳定的Lu1-xInxFeO3六角铁氧体陶瓷。XRD及透射电镜分析结果表明在x=0.4～0.75成分范围内得到了稳定的六角结构,且随着In离子含量的增加,其结构逐渐由极性的P63cm转变为非极性的P63/mmc。在HAADF像中观察到了畴界,证实了其铁电性,通过模拟计算其局域自发极化值约为1.73μC/cm2。同时,该极性相的反铁磁奈尔温度高于室温,证明了其室温下的反铁磁序。由于DM相互作用,低温自旋重取向温度下表现出弱铁磁性。低温自旋重取向转变伴随介电异常,也证明了其强的自旋晶格耦合,即磁电耦合效应。通过对六角Lu1-xInxFeO3陶瓷介电性能及X射线光电子能谱(XPS)的分析,揭示了其介电响应与漏导机制。其中低温介电弛豫与Fe3+/Fe2+的电荷跃迁有关。而高温介电弛豫是典型的Debye型介电弛豫,其起源与氧空位相关。Lu1-xInxFeO3陶瓷高电导的起源于Fe3+与Fe2+离子的电荷跃迁。
[Abstract]:In recent years, due to its rich physical connotation and broad application prospects, multi ferromagnetic materials have been paid more and more attention and research. This paper has studied the preparation, structure and performance regulation of two kinds of Fe based single-phase multi iron materials of BiFeO3 and h-LuFeO3, and obtained the following main conclusions. Through the formation of Sr0.5Ca0.5TiO3 The structure of BiFeO3 based ceramics gradually changed from siderite to orthogonal structure. The formation of the solid solution significantly reduced the electrical conductivity of BiFeO3 ceramics. The ferroelectric properties of x=0.25 and 0.3 two components were obviously improved. The improvement of ferroelectric properties could be attributed to the decrease of leakage current density. The optimum magnetic energy was obtained at =0.25 and the residual magnetization was obtained. The enhancement of the magnetic energy of up to Mr=34.8emu/mol. is attributed to the replacement of Fe3+ ions by Ti4+ ions, which destroys the spatial modulation of the spiral spin magnetic structure.Sr/Ca on the structure and performance of BiFeO3- (Sr, Ca) TiO3 ceramics. With the increase of the Sr/Ca ratio, the diamond square orthogonal phase boundary is gradually moving towards (Sr, Ca) TiO3. The best ferroelectric performance appears. The magnetic energy is rich near the phase boundary. The magnetic energy is mainly affected by the displacement of B bit. The best magnetic properties are obtained when the displacement of B bit is 20% ~ 25%. In the (1-x) BiFeO3-x (0.5CaTiO3-0.5SmFeO3) three system ceramics, the ceramic structure gradually changes from the R3c (x < 0.2) to the orthogonal Pbnm (x > 0.3) with the increase of X, and a small number of intermediate phases appear. It is very wide. The content of polar R3c and non polar Pbnm is coexisting in one component range, and the content of the two phase changes with the change of X. The dielectric and DSC analysis results show that there is obvious thermal hysteresis in the components of x < 0.2. This indicates that the component of the main phase is R3c is a typical dispersion ferroelectrics with the characteristics of the first order ferroelectric phase transition. With the further increase of X, dielectric There are two dielectric relaxation processes with apparent frequency dispersion and two dielectric relaxation processes. The dielectric relaxation is related to the grain boundary. The low temperature dielectric relaxation is related to the charge transfer between Fe2+ and Fe3+. The ferroelectric property is obviously enhanced in several components of X less than 0.2, which is related to its internal polarity phase. The improvement of the magnetic energy of the best magnetic energy Mr=63.2emu/mol. at room temperature is attributed to the substitution of Ti ions to destroy the Fe-O-Fe super exchange. In addition, the replacement of the magnetic rare earth Sm ions is the main reason for the significant improvement of the magnetic properties at low temperature. The stable Lu1-xInxFeO3 six angles are obtained by In separation in LuFe03. The.XRD and transmission electron microscope analysis of ferrite ceramics showed that a stable six angle structure was obtained within the range of x=0.4 to 0.75, and with the increase of In ion content, the structure gradually changed from polar P63cm to non polar P63/mmc. in the HAADF image, and the domain boundary was observed in the HAADF image. The ferroelectric property was confirmed and the local spontaneous pole was calculated by simulation. The antiferromagnetic Nair temperature of the polar phase is higher than room temperature, and the antiferromagnetic Nair temperature of the polar phase is higher than room temperature. It is proved that the antiferromagnetic order at room temperature. Because of the DM interaction, the low temperature spin reorientation temperature shows weak ferromagnetism. The transition of the low temperature spin reorientation is accompanied by the dielectric anomaly, and the strong spin lattice coupling, that is, the magnetoelectric coupling effect is also proved. Through the analysis of dielectric properties and X ray photoelectron spectroscopy (XPS) of six angle Lu1-xInxFeO3 ceramics, the dielectric response and leakage mechanism are revealed. The dielectric relaxation at low temperature is related to the charge transition of Fe3+/Fe2+. High temperature dielectric relaxation is a typical Debye type dielectric relaxation, and its origin is related to the high conductivity of.Lu1-xInxFeO3 ceramics related to oxygen vacancy. The charge transition of Fe3+ and Fe2+ ions is derived.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ174.1

【参考文献】