發(fā)布時(shí)間：2018-05-03 00:46

  本文選題：BiFeO_3 + 六角稀土鐵氧體�。� 參考：《浙江大學(xué)》2017年博士論文

【摘要】：近年來,多鐵性材料由于其豐富的物理內(nèi)涵和廣闊的應(yīng)用前景,得到了越來越廣泛的關(guān)注與研究。本論文以BiFeO3和h-LuFeO3兩類Fe基單相多鐵材料為研究對(duì)象,系統(tǒng)研究了其制備、結(jié)構(gòu)與性能調(diào)控,獲得如下主要結(jié)論。通過與Sr0.5Ca0.5TiO3形成固溶體,BiFeO3基陶瓷的結(jié)構(gòu)逐漸由菱方變?yōu)檎唤Y(jié)構(gòu)。該固溶體的形成顯著降低了 BiFeO3陶瓷的電導(dǎo)率,x=0.25及0.3兩組分的鐵電性能得到明顯的改善。鐵電性能的改善可歸因于漏電流密度的降低。最佳磁性能在=0.25時(shí)得到,剩余磁化強(qiáng)度高達(dá)Mr=34.8emu/mol。磁性能的增強(qiáng)主要?dú)w因于Ti4+離子置換Fe3+離子,破壞了空間調(diào)制的螺旋自旋磁結(jié)構(gòu)。Sr/Ca比對(duì)BiFeO3-(Sr,Ca)TiO3陶瓷的結(jié)構(gòu)與性能有顯著的影響。隨著Sr/Ca比的增大,菱方-正交相界逐漸向(Sr,Ca)TiO3一端移動(dòng)。最佳鐵電性能出現(xiàn)在相界附近富菱方相。磁性能主要受B位置換的影響,在B位置換量為20%～25%時(shí)得到最佳磁性能。在(1-x)BiFeO3-x(0.5CaTiO3-0.5SmFeO3)三元系陶瓷中,隨x的增加,陶瓷結(jié)構(gòu)逐漸由菱方的R3c(x≤0.2)變?yōu)檎籔bnm(x≥0.3),且有少量中間相出現(xiàn)。在很寬的一個(gè)成分范圍內(nèi)極性R3c與非極性Pbnm兩相共存,且兩相的含量隨x的變化而改變。介電及DSC分析結(jié)果表明,在x≤0.2的組分中存在明顯的熱滯,這說明主相為R3c的成分是典型的彌散鐵電體,具有一級(jí)鐵電相變的特征。隨著x的進(jìn)一步增加,介電常數(shù)出現(xiàn)明顯的頻率色散,且存在兩個(gè)介電弛豫過程。高溫介電弛豫與晶界相關(guān),低溫介電弛豫與Fe2+和Fe3+之間的電荷轉(zhuǎn)移相關(guān)。鐵電性能在x≤0.2的幾個(gè)成分內(nèi)得到了明顯的增強(qiáng),這與其內(nèi)部的極性相R3c相關(guān)。同時(shí),磁性能測(cè)試表明,磁性能得到了顯著的改善,室溫下最佳磁性能Mr=63.2emu/mol。磁性能的增強(qiáng)主要?dú)w因于Ti離子的置換破壞Fe-O-Fe超交換作用。此外,磁性稀土 Sm離子的置換是低溫磁性能顯著改善的主要原因。在LuFe03中通過In離子置換,獲得了穩(wěn)定的Lu1-xInxFeO3六角鐵氧體陶瓷。XRD及透射電鏡分析結(jié)果表明在x=0.4～0.75成分范圍內(nèi)得到了穩(wěn)定的六角結(jié)構(gòu),且隨著In離子含量的增加,其結(jié)構(gòu)逐漸由極性的P63cm轉(zhuǎn)變?yōu)榉菢O性的P63/mmc。在HAADF像中觀察到了疇界,證實(shí)了其鐵電性,通過模擬計(jì)算其局域自發(fā)極化值約為1.73μC/cm2。同時(shí),該極性相的反鐵磁奈爾溫度高于室溫,證明了其室溫下的反鐵磁序。由于DM相互作用,低溫自旋重取向溫度下表現(xiàn)出弱鐵磁性。低溫自旋重取向轉(zhuǎn)變伴隨介電異常,也證明了其強(qiáng)的自旋晶格耦合,即磁電耦合效應(yīng)。通過對(duì)六角Lu1-xInxFeO3陶瓷介電性能及X射線光電子能譜(XPS)的分析,揭示了其介電響應(yīng)與漏導(dǎo)機(jī)制。其中低溫介電弛豫與Fe3+/Fe2+的電荷躍遷有關(guān)。而高溫介電弛豫是典型的Debye型介電弛豫,其起源與氧空位相關(guān)。Lu1-xInxFeO3陶瓷高電導(dǎo)的起源于Fe3+與Fe2+離子的電荷躍遷。
[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.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ174.1

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本文編號(hào)：1836234