PrBi4Fe0.5Co0.5Ti3O15多铁陶瓷的性能研究

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陈春霞, 李浩然, 郑仁奎. PrBi₄Fe_0.5Co_0.5Ti₃O₁₅多铁陶瓷的性能研究 . 无机材料学报, 2015, 30(5): 511-515
CHEN Chun-Xia, LI Hao-Ran, ZHENG Ren-Kui. Properties of Multiferroic PrBi₄Fe_0.5Co_0.5Ti₃O₁₅ Ceramics . Journal of lnorganic Materials,2015, 30(5): 511-515 复制到剪切板

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PrBi₄Fe_0.5Co_0.5Ti₃O₁₅多铁陶瓷的性能研究

陈春霞^1,², 李浩然², 郑仁奎²

1. 安庆师范学院物理与电气工程学院, 安庆246000

2. 中国科学院上海硅酸盐研究所, 上海200050

郑仁奎, 研究员. E-mail:zrk@mail.sic.ac.cn

作者简介: 陈春霞(1969-), 女, 副教授. E-mail: ccxhzq@163.com

基金:国家自然科学基金(51172259)

摘要

采用传统固相反应法与两步合成法制备了PrBi₄Fe_0.5Co_0.5Ti₃O₁₅陶瓷, 研究了Pr与Co共掺杂对Bi₅FeTi₃O₁₅陶瓷的结构、磁性能以及介电性能的影响。X射线衍射分析显示, 传统固相反应法制备的样品比两步法制备的样品更容易形成单相结构。铁电和磁性测量证明样品具有多铁性, 并且Pr与Co共掺杂能大幅提高材料的磁性能, 固相反应法与两步合成法制备的样品在室温下的剩余磁化强度(2 M_r)分别为0.315, 0.576 Am²/kg, 比文献报道的Bi₅FeTi₃O₁₅陶瓷的2 M_r ( 2.7×10^-6 Am²/kg ) 高5个数量级, 比掺Co的Bi₅Fe_0.5Co_0.5Ti₃O₁₅陶瓷2 M_r ( 7.8×10^-3 Am²/kg ) 高2个数量级。

关键词: 多铁陶瓷; 固相反应法; 磁性能; 介电性能

中图分类号:O469;O432 文献标志码:A 文章编号:1000-324X(2015)05-0511-05

Properties of Multiferroic PrBi₄Fe_0.5Co_0.5Ti₃O₁₅ Ceramics

CHEN Chun-Xia^1,², LI Hao-Ran², ZHENG Ren-Kui²

1. School of Physics and Electrical Engineering, Anqing Teacher College, Anqing 246000, China

2. Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

Fund:National Natural Science Foundation of China (51172259)

Abstract

PrBi₄Fe_0.5Co_0.5Ti₃O₁₅ compounds were prepared either by conventional solid-state reaction method or by two-step method. X-ray diffraction analyses indicate that the PrBi₄Fe_0.5Co_0.5Ti₃O₁₅samples which were synthesized by the conventional solid-state reaction method favors the formation of single phase four-layer Aurivillius phase more easily than the samples prepared by the two-step method. The multiferroic properties of the samples at room temperature were demonstrated by ferroelectric and magnetic measurements. The samples exhibit significantly enhanced magnetic properties by Pr/Co co-substitution. The remnant magnetization (2 M_r) of the samples prepared by the conventional solid-state reaction and two-step methods are 0.315 and 0.576 Am²/kg, respectively, approximately five orders larger than that of the reported Bi₅FeTi₃O₁₅ ceramics (2.7×10^-6 Am²/kg) and two orders of the reported Co-doped Bi₅FeTi₃O₁₅ ceramics (7.8×10^-3 Am²/kg).

Keyword: multiferroic ceramics; solid state reaction; magnetic property; dielectric property

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近年来, 多铁材料由于具有基础研究和应用研究的双重价值而受到广泛关注^{[1, 2, 3]}。一方面, 铁电性与铁磁性的共存和相互作用, 使其具有磁电耦合性能, 大大拓宽了材料的应用范围; 另一方面, 自旋、电荷和轨道等自由度相互关联, 为研究强关联系统提供了平台。但是铁磁性和铁电性具有互斥性^[4], 具有磁电耦合效应的单相多铁性材料非常有限, 主要体系有铋系钙钛矿 (以BiFeO₃、BiMnO₃为代表)及稀土锰酸盐钙钛矿(RMnO₃、RMn₂O₅, R=Gd、Tb、Dy、Ho等)两大类^{[5, 6]}。在这些单相多铁性材料中, 多数体系的奈尔温度T_N及居里温度T_C都很低, 并且磁电耦合效应随温度升高很快减弱。BiFeO₃是少数室温下同时存在铁电性和弱铁磁性的单相多铁材料之一, 其铁电居里温度(T_C)约为1100 K, 反铁磁性的奈尔温度(T_N)约为640 K, 但BiFeO₃材料的高漏电流和室温下的弱铁磁性等因素极大地限制了它的应用^{[7, 8]}。

近年来, Bi₅FeTi₃O₁₅(BFTO)作为一个很有应用前景的多铁材料受到广泛关注^{[9, 10]}。BFTO可以看作是由具有良好铁电性的结构单元Bi₄Ti₃O₁₂和具有弱铁磁性的结构单元BiFeO₃在原子层次上沿c轴方向周期性堆积而成。Bi₄Ti₃O₁₂是Aurivillius材料体系中最具代表性的铁电材料之一, 也是无铅压电材料研究中备受关注的候选材料, 其基本结构为相邻的两个铋氧层间有三层钙钛矿结构的TiO₆八面体。铋氧层具有空间电荷库和绝缘层的双重作用, 能够有效地降低多铁材料的电导, 改善漏电流行为, 正是这种作用保持了Bi₄Ti₃O₁₂内在的铁电性能, 也使BFTO在室温下具有较好的铁电性。BFTO的磁性能与其B位的磁性离子Fe³⁺有关, 变温磁性能研究表明该样品的低温磁性来源于反铁磁(AFM)作用背景下的超顺磁态, 因此, 在室温下BFTO的铁电性与反铁磁性共存, 其奈尔温度约为80K。如果要使BFTO可以实际应用, 必须对其磁性能加以改善。一般认为加强磁性离子之间的相互耦合可以提高材料的铁磁性, 如果采用过渡金属磁性离子掺杂取代BFTO中的Fe³⁺, 有望增强样品内不同磁性离子之间的相互耦合, 从而改善磁性能^{[11, 12, 13]}。Mao等^[11]通过Co³⁺对Fe³⁺的取代制备得到Bi₅Fe_0.5Co_0.5Ti₃O₁₅(BFCTO)陶瓷, 使其铁磁性得到明显提高; Yang等^[13]研究发现, 在Co掺杂的基础上, Bi位掺杂Nd能进一步提高材料的磁性。稀土元素Pr离子磁矩相对较高(约为3.5 μ B), 替代BFTO中的Bi³⁺离子, 可以有效提高样品的磁性能; 同时Pr离子具有+3、+4两种价态, 可以抑制氧空位, 改善漏电流, 降低介电损耗, 提高材料介电性能^[14]; 另外, Pr³⁺、Pr⁴⁺离子半径不同, 可能诱导结构相变, 进一步提高BFTO多铁性能^[15]。因此, 本工作采用传统固相法与两步合成法分别制备了PrBi₄Fe_0.5Co_0.5Ti₃O₁₅陶瓷, 以探讨Pr与Co共掺杂对BFTO陶瓷的微结构、铁磁和介电等性能的影响。

1 实验方法

采用传统固相烧结法制备PrBi₄Fe_0.5Co_0.5Ti₃O₁₅-1 (简记为Pr-1 ) 与BFTO样品。选用纯度超过99.9%的Bi₂O₃、TiO₂、Pr₆O₁₁、Fe₂O₃和Co₂O₃粉末为原料, 按化学计量比配好原料, 放入尼龙球磨罐中, 并加入适量的无水乙醇作分散剂, 连续球磨12 h后在800℃预合成8 h。取出预合成粉料再次球磨12 h, 然后加入粘结剂PVA, 充分混合后压成ϕ 10 mm× 1.0 mm的圆片, 在1020℃烧结2 h, 随炉冷却, 得到成瓷良好的样品。

采用两步合成法制备PrBi₄Fe_0.5Co_0.5Ti₃O₁₅-2 (Pr-2)样品。首先, 按Bi₄Ti₃O₁₂的化学计量配比称量高纯Bi₂O₃和TiO₂粉末, 经12 h球磨混合均匀后, 在800℃预烧8 h, 制成Bi₄Ti₃O₁₂粉末备用。然后, 将预合成的Bi₄Ti₃O₁₂、Pr₆O₁₁、Fe₂O₃和Co₂O₃粉末按化学计量比配好, 球磨12 h后在800℃预烧8 h, 再次球磨12 h, 压片后在1020℃烧结2 h制成Pr-2样品。

采用多晶 X射线粉末衍射仪 (Bruker D8 Advance)分析样品成相情况与晶体结构, 采用SQUID magnetometer (Quantum Design, MPMS XL-5)测量样品磁性; 采用介电频谱仪(Agilent E4980)测量样品的变温介电特性; 由铁电分析仪(Radiant Technologies, Multiferroic)测得室温下样品的电滞回线。

2 结果与讨论

图1(a)和(b)分别为Pr-2和Pr-1样品的粉末X射线衍射(XRD)图谱, 为了便于比较, 图1(c)给出了未掺杂的BFTO的 XRD 图谱。BFTO的所有衍射峰均可以按照Bi₅FeTi₃O₁₅的标准谱(JCPDF: 82-0063) 进行指标化。与BFTO衍射谱比较, Pr-1样品的谱线形状与BFTO能较好地对应, 表明样品形成了四层铋系钙钛矿相, 衍射峰的位置有少许移动, 这可能是由于不同离子半径的离子掺杂造成的晶格畸变; 而Pr-2样品的谱线则在10.8° 、27.4° 和38.3° 位置(图中* 表示)出现了明显杂峰, 分析表明这些杂峰归属于Bi₄Ti₃O₁₂相, 说明材料中可能存在部分三层结构, 形成了少量的共生结构。这一结果表明, 传统固相反应法比两步合成法制备的样品更容易形成单相结构。图 2和图3 分别为Pr-1、Pr-2样品在300 K与10 K温度下的磁滞回线图, 为了比较, 图中还给出了BFTO的磁滞回线图。首先, 可以发现两种合成方法得到的样品谱线形状相似, Pr-1、Pr-2 样品在室温下均呈现狭长的磁滞回线图。从局部放大图可以看出(图2插图), Pr-1、Pr-2样品表现出明显的铁磁性, 谱线形状基本一致, 说明这两种合成方法对磁性能的影响并不大, 但相对于BFTO样品近似直线的M-H关系, 磁性能都得到极大的提升。其次, 室温下, Pr-1、Pr-2样品的剩余磁量级^[11], 与Yang等^[13]用Nd取代Bi的BNFCT陶瓷的实验结果基本相同(2M_r约0.33 Am²/kg)。低温下样品磁滞回线明显宽化, 矩形度变好, Pr-1、Pr-2样品2M_r分别为3.118、2.980 Am²/kg(图3)。

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	图1 (a)Pr-2、(b)Pr-1和(c)BFTO粉末样品的XRD图谱Fig. 1 Powder X-ray diffraction patterns of samples (a) Pr-2, (b) Pr-1 and (c) BFTO

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	图2 Pr-1、Pr-2和BFTO样品在300 K时的磁滞回线Fig. 2 Magnetic hysteresis loops of Pr-1, Pr-2 and BFTO samples at 300 K

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	图3 Pr-1、Pr-2和BFTO样品在10 K时的磁滞回线Fig. 3 Magnetic hysteresis loops of Pr-1, Pr-2 and BFTO samples at 10 K

化2M_r分别为 0.315、0.576 Am²/kg, 这比文献报道的BFTO陶瓷2.7 Am²/kg的2M_r高5个数量级^[16], 比BFCTO陶瓷7.8 Am²/kg的2M_r高约2个数

从以上实验结果可以看出, Pr 与Co共掺杂显著地提升了材料的铁磁性, 其原因存在不同的解释。Mao等^[11]认为铁磁性可能来源于 Fe-O-Co 的铁磁耦合相互作用; Yang等^[13]则认为这种提升可能是掺杂导致的结构畸变削弱了反铁磁作用所致。从前述分析可以看到, 稀土Pr掺杂的样品比BFCTO陶瓷的2M_r高约2个数量级, 因此可以认为磁性的提升除了与上述两种因素有关, 可能还由于Pr的离子半径小于Bi的离子半径, Pr掺杂以后引起晶格畸变, 改变了磁性离子耦合键长、键角, 从而提高样品磁性。

图4给出了样品在零磁场下冷却(ZFC)与外加磁场场下冷却(FC)的磁化强度随温度变化关系曲线, 测量所用的磁场强度为3.98 A/m。从图4可以看出, Pr-1、Pr-2样品ZFC与FC磁化强度在温度降低过程中均出现了明显的分离, 并在分离后继续上升, 表明体系中发生了顺磁-铁磁性转变。当温度降到200 K以下时, ZFC开始减小, 到150 K以下, 出现新的平台, 呈现类团簇玻璃态磁特性。究其原因可能是由于掺杂的Co离子进入了两个铋氧层间的钙钛矿结构的晶格位置且随机分布, 从而出现局域的Fe-O-Co铁磁交换作用, 但由于Fe和Co离子总数只占总的过渡金属离子(指Fe、Co和Ti离子)数的1/4, 这意味着Fe-O-Co不能形成长程交换作用, 只能形成局域的铁磁团簇, 从而使得该体系出现类团簇玻璃态的磁特性。值得指出的是, 未掺杂的BFTO样品(图4插图), ZFC与FC曲线几乎重合, 与文献[17]报道的一致, 这一结果再次表明, 掺入Pr与Co改变了BFTO反铁磁特征, 使其呈现明显铁磁性。

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	图4 Pr-1、Pr-2和BFTO样品的ZFC和FC磁化强度与温度关系曲线Fig. 4 ZFC and FC magnetization curves of Pr-1, Pr-2 and BFTO samples

图5为Pr-1、Pr-2样品的电滞回线, 测量频率为100 Hz。从图5可以看出, 虽然在60 kV/cm 的电场作用下, 样品的电滞回线均未达到饱和状态, 但与BFTO样品相比, Pr与Co共掺杂对样品的铁电性能有所改善。

铋层状材料是典型的位移型铁电体, 研究表明其自发极化主要来源于三个方面: (1)B位离子的移动; (2)氧八面体沿c轴倾斜; (3)氧八面体在ab面内的旋转。一般认为A位稀土离子掺杂可以减少高温下由于Bi挥发而产生氧空位的几率, B位掺杂能有效提高材料电阻率, 从而提高材料的铁电性能。在本实验中, 掺杂的优势在提升铁电性能中虽然有所体现, 但所有样品总体铁电性能较弱。为了分析其原因, 实验对样品进行了形貌观察, 图 6 为Pr-1、Pr-2与BFTO陶瓷的场发射扫描电子显微镜(SEM)表面及断面照片, 从表面形貌照片中可以看到晶粒呈典型层状钙钛矿片状结构, 但晶粒大小不均匀, BFTO样品平均晶粒比Pr-1和Pr-2样品的晶粒尺寸要大一倍左右, 同时, 还可发现Pr-1样品晶粒尺寸分布更均匀。从断面形貌还可看到样品均有一些细小的孔洞, BFTO尤其明显, 这也许是导致样品无法进一步提高测试电场, 铁电行为表现不好的主要原因。

图7(a)和(b)分别为1000 Hz下的Pr-1与Pr-2样品的相对介电常数( )与损耗( )温度谱。从图7(a)中可见, 随着温度的升高, 增大, 但在本实验测量范围内, 相对介电常数温度谱没有出现峰值, 说明铁电-顺电相变的居里温度高于425 K。图7(b)表明, 在测量温度范围内, 介电损耗均小于3%, Pr 掺杂未明显损害材料的热稳定性, 且Pr-1比Pr-2介电损耗小, 说明Pr-2结构有更多缺陷, 这点与XRD测量结果存在杂相相一致。

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	图5 Pr-1、Pr-2和BFTO样品的电滞回线Fig. 5 P-E hysteresis loops of Pr-1, Pr-2 and BFTO samples at frequency of 100 Hz

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	图6 Pr-1、Pr-2和BFTO样品表面(a, c, e)与断面(b, d, f)SEM照片Fig. 6 Surface (left) and cross-sectional (right) SEM images for Pr-1, Pr-2 and BFTO Surface SEM images for (a) Pr-1, (c) Pr-2, (e) BFTO; cross-sectional SEM images for (b) Pr-1, (d) Pr-2, (f) BFTO

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	图7 (a)Pr-1与Pr-2样品相对介电常数温度谱; (b)Pr-1与Pr-2样品损耗温度谱Fig. 7 Temperature dependence of (a) dielectric constants (ε _r) and (b) dielectric loss (tanδ) of Pr-1 and Pr-2 samples at 1000 Hz

从损耗曲线还可以看到在330 K附近有一个微小的峰值, 而介电谱上对应温度却没有明显的峰值, 所以损耗曲线上的这个峰值并非对应铁电-顺电相变时的居里温度。这个峰值的出现可以根据德拜公式来解释:

其中为稳态介电系数, 为光频介电系数, 为特征时间, 随温度上升而减小。

结合图7(b)可以看出, 当温度低于250 K时, 较大, 由德拜关系式可知, , 故在此温度范围内, 随着温度上升, 减小, 上升; 当温度升高到350 K左右, 较小, 此时 , 因而 , 在此温度范围内, 随着温度上升, 减小, 减小, 于是在某一温度时, 有极大值, 相应地, 损耗曲线出现峰值; 当温度继续升高到360 K以上, 电导损耗剧烈上升, 也随温度上升急剧上升。

3 结论

采用传统固相法与两步合成法制备了Pr离子与Co离子共掺杂的PrBi₄Fe_0.5Co_0.5Ti₃O₁₅多铁性陶瓷, 铁电和磁性测量证明样品具有多铁性。

1) X射线衍射测试结果表明, 采用传统固相反应法比采用两步法制备的样品更容易形成单相四层Aurivillius结构。

2) 磁性测量结果表明, Pr和Co离子共掺杂后样品的铁磁性能明显改善, 室温下Pr-1、Pr-2的样品的2M_r分别为0.315、0.576 Am²/kg; 在低温下, 该体系呈现类团簇玻璃态磁特性。

3) 介电性能测量显示, 损耗曲线在330 K附近出现一个峰值, 分析认为该峰并非对应于顺电– 铁电相变, 但可以用德拜模型加以解释。

参考文献

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[1]	JEONG JAEHONG, LE MANH DUC, BOURGES P, et al. Temperature-dependent interplay of dzyaloshinskii-moriya interaction and single-ion anisotropy in multiferroic BiFeO₃. Physics Review Letters, 2014, 113(10): 107202. [本文引用:1] [JCR: 7.943]
[2]	WALKER H C, FABRIZI F, PAOLASINI L, et al. Femtoscale magnetically induced lattice distortions in multiferroic TbMnO₃. Science, 2011, 333(6047): 1273-1276. [本文引用:1]
[3]	RAMAZANOGLU M, RATCLIFF II W, YI H T, et al. Giant effect of uniaxial pressure on magnetic domain populations in multiferroic bismuth ferrite, Physics Review Letters, 2011, 107(6): 067203. [本文引用:1] [JCR: 7.943]
[4]	NICOLA A. HILL, Why are there so few magnetic ferroelectrics?J. Phys. Chem. B, 2000, 104(29): 6694-6709. [本文引用:1] [JCR: 3.607]
[5]	ATOU T, CHIBA H, OHOYAMA K, et al. Structure determination of ferromagnetic perovskite BiMnO₃, Journal of Solid State Chemistry, 1999, 145(2): 639-642. [本文引用:1] [JCR: 2.04]
[6]	KIMURA T, LAWES G, GOTO T, et al. Magnetoelectric phase diagrams of orthorhombic RMnO₃ (R=Gd, Tb, and Dy). Physical Review B, 2005, 71(22): 224425. [本文引用:1]
[7]	SONG WEI, WANG XUAN, ZHANG DONG, et al. Preparation and characterization of multiferroics BiFeO₃. Journal of Inorganic Materials, 2012, 27(10): 1053-1057. [本文引用:1] [JCR: 0.537] [CJCR: 1.106]
[8]	DAS S R, CHOUDHARY R N P, HATTACHARYA P B, et al. Structural and multiferroic properties of La-modified BiFeO₃ ceramics. J. Appl. Phys. , 2007, 101(3): 034104-1-7. [本文引用:1]
[9]	SNEDDEN A, HERVOCHES C H, LIGHEFOOT P. Ferroelectric phase transitions in SrBi₂Nb₂O₉ and Bi₅FeTi₃O₁₅: a powder neutron diffraction study, Phys. Rev. B, 2003, 67(9): 092102. [本文引用:1]
[10]	SINGH R S, BHIMASANKARAM T, KUMAR G S, et al. Dielectric and magnetoelectric properties of Bi₅FeTi₃O₁₅. Solid State Commun. , 1994, 91(7): 567-569. [本文引用:1] [JCR: 1.534]
[11]	MAO XIANG-YU, WANG WEI, CHEN XIAO-BING, et al. Multiferroic properties of layer-structured Bi₅Fe_{0. 5}Co_{0. 5}Ti₃O₁₅ ceramics, Appl. Phys. Lett. , 2009, 95(8): 082901. [本文引用:4] [JCR: 3.794]
[12]	MAO XIANG-YU, WANG WEI, SUN HUI, et al. Influence of different synthesizing steps on the multiferroic properties of Bi₅FeTi₃O₁₅ and Bi₅Fe_{0. 5}Co_{0. 5}Ti₃O₁₅ ceramics. J. Mater. Sci. , 2012, 47(6): 2960-2965. [本文引用:1] [JCR: 1.486]
[13]	YANG F J, SU P, WEI C, et al. Large magnetic response in (Bi₄Nd)Ti₃(Fe_{0. 5}Co_{0. 5})O₁₅ ceramic at room-temperature. J. Appl. Phys. , 2011, 110(12): 126102-1-3. [本文引用:4]
[14]	PRAKASH CHANDRA SATI, MANISHA ARORA, SUNIL CHAUHAN, et al. Structural, magnetic, vibrational and impedance properties of Pr and Ti codoped BiFeO₃ multiferroic ceramics. Ceramics International, 2014, 40(6): 7805-7816. [本文引用:1] [JCR: 1.789]
[15]	NEERAJ KUMARA, NEERAJ PANWARB, BHASKER GAHTORIA, et al. Structural, dielectric and magnetic properties of Pr substituted Bi₁-_xPr_xFeO₃(0≤x≤0. 15) multiferroic compounds. Journal of Alloys and Compounds, 2010, 501(2): L29-L32. [本文引用:1] [JCR: 2.39]
[16]	MAO X Y, WANG W, CHEN X B. Electrical and magnetic properties of Bi₅FeTi₃O₁₅ compound prepared by inserting BiFeO₃ into Bi₄Ti₃O₁₂. Solid State Communications, 2008, 147(5/6): 186-189. [本文引用:1] [JCR: 1.534]
[17]	DONG X W, WANG K F, WAN J G, et al. Magnetocapacitance of polycrystalline Bi₅FeTi₃O₁₅ prepared by Sol-Gel Method. J. Appl. Phys. , 2008, 103(9): 094101. [本文引用:1]

2014

7.943

0.0

Physics Review Letters. 2014, 113(10):107202-

Temperature-dependent interplay of dzyaloshinskii-moriya interaction and single-ion anisotropy in multiferroic BiFeO₃.

JEONG JAEHONG , LE MANH DUC , BOURGES P

Low-energy magnon excitations in multiferroic BiFeO 3 were measured in detail as a function of temperature around several Brillouin zone centers by inelastic neutron scattering experiments on single crystals. Unique features around 1 meV are directly associated with the interplay of the Dzyaloshinskii-Moriya interaction and a small single-ion anisotropy. The temperature dependence of these and the exchange interactions were determined by fitting the measured magnon dispersion with spin-wave calculations. The spectra best fit an easy-axis type magnetic anisotropy and the deduced exchange and anisotropy parameters enable us to determine the anharmonicity of the magnetic cycloid. We then draw a direct connection between the changes in the parameters of spin Hamiltonian with temperature and the physical properties and structural deformations of BiFeO 3 .

... 近年来, 多铁材料由于具有基础研究和应用研究的双重价值而受到广泛关注^[1,2,3] ...

2011

0.0

Science. 2011, 333(6047):1273-1276

Femtoscale magnetically induced lattice distortions in multiferroic TbMnO₃.

WALKER H C , FABRIZI F , PAOLASINI L

Magneto-electric multiferroics exemplified by TbMnO 3 possess both magnetic and ferroelectric long-range order. The magnetic order is mostly understood, whereas the nature of the ferroelectricity has remained more elusive. Competing models proposed to explain the ferroelectricity are associated respectively with charge transfer and ionic displacements. Exploiting the magneto-electric coupling, we used an electric field to produce a single magnetic domain state, and a magnetic field to induce ionic displacements. Under these conditions, interference between charge and magnetic x-ray scattering arose, encoding the amplitude and phase of the displacements. When combined with a theoretical analysis, our data allow us to resolve the ionic displacements at the femtoscale, and show that such displacements make a substantial contribution to the zero-field ferroelectric moment.

... 近年来, 多铁材料由于具有基础研究和应用研究的双重价值而受到广泛关注^[1,2,3] ...

2011

7.943

0.0

Physics Review Letters. 2011, 107(6):067203-

Giant effect of uniaxial pressure on magnetic domain populations in multiferroic bismuth ferrite,

RAMAZANOGLU M , RATCLIFF II W , YI H T

Neutron diffraction is used to show that small ( ∼ 7 MPa , or 70 bar) uniaxial pressure produces significant changes in the populations of magnetic domains in a single crystal of 2% Nd-doped bismuth ferrite. The magnetic easy plane of the domains converted by the pressure is rotated 60° relative to its original position. These results demonstrate extreme sensitivity of the magnetic properties of multiferroic bismuth ferrite to tiny (less than 10 − 4 ) elastic strain, as well as weakness of the forces pinning the domain walls between the cycloidal magnetic domains in this material.

... 近年来, 多铁材料由于具有基础研究和应用研究的双重价值而受到广泛关注^[1,2,3] ...

2000

3.607

0.0

J. Phys. Chem. B. 2000, 104(29):6694-6709

HILL, Why are there so few magnetic ferroelectrics?

NICOLA A.

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

... 但是铁磁性和铁电性具有互斥性^[4], 具有磁电耦合效应的单相多铁性材料非常有限, 主要体系有铋系钙钛矿 (以BiFeO₃、BiMnO₃为代表)及稀土锰酸盐钙钛矿(RMnO₃、RMn₂O₅, R=Gd、Tb、Dy、Ho等)两大类^[5,6] ...

1999

2.04

0.0

Journal of Solid State Chemistry. 1999, 145(2):639-642

Structure determination of ferromagnetic perovskite BiMnO₃,

ATOU T , CHIBA H , OHOYAMA K

Structure of feromagnetic BiMnO 3 synthesized at high pressure has been determined by electron diffraction and neutron powder diffraction. This structure is related to a heavily distorted perovskite structure, having monoclinic symmetry, space group C 2, with a =9.5323(6) Å, b =5.6064(3) Å, C = 9.8535(7) Å, and β =110.667(5)°. The distortion is caused by a polarized Bi 6 s 2 lone pair. Every trivalent manganese cation reveals the Jahn–Teller distortion and ordering of a vacant d x 2 − y 2 orbital is suggested to play an important role for the ferromagnetism.

2005

0.0

Physical Review B. 2005, 71(22):224425-

Magnetoelectric phase diagrams of orthorhombic RMnO₃ (R=Gd, Tb, and Dy).

KIMURA T , LAWES G , GOTO T

Magnetoelectric phase diagrams have been investigated for rare-earth manganites with orthorhombically distorted perovskite structure, R MnO 3 ( R = Gd , Tb, and Dy). A variety of magnetic and electric phases emerge with varying R -site ion, temperature, and magnetic field in these systems. The magnetoelectric phase diagram varies sensitively with the direction of a magnetic field relative to the crystallographic axes. Although the ground state of GdMnO 3 with the largest ionic radius of R ( r R ) is not ferroelectric in zero magnetic fields ( H = 0 ) , a ferroelectric phase with electric polarization ( P ) along the a axis appears by applying H ( > ∼ 1 T ) along the b axis. Both TbMnO 3 and DyMnO 3 show a ferroelectric order with P along the c axis even at H = 0 below a lock-in transition temperature where nonzero wave vectors for magnetic and lattice modulations become nearly constant. These systems also exhibit a flop of the ferroelectric polarization ( P ∥ c to P ∥ a ) when H is applied along the a or b axis. By contrast, the application of H above ∼ 10 T along the c axis completely suppresses the ferroelectricity in TbMnO 3 . Possible origins of the observed evolution of magnetoelectric phases are discussed in consideration of magnetism and lattice distortion in the perovskite rare-earth manganites.

2012

0.537

1.106

... BiFeO₃是少数室温下同时存在铁电性和弱铁磁性的单相多铁材料之一, 其铁电居里温度(T_C)约为1100 K, 反铁磁性的奈尔温度(T_N)约为640 K, 但BiFeO₃材料的高漏电流和室温下的弱铁磁性等因素极大地限制了它的应用^[7,8] ...

2007

0.0

2003

0.0

Phys. Rev. B. 2003, 67(9):092102-

Ferroelectric phase transitions in SrBi₂Nb₂O₉ and Bi₅FeTi₃O₁₅: a powder neutron diffraction study,

SNEDDEN A , HERVOCHES C H , LIGHEFOOT P.

Structural phase transitions in the Aurivillius phase ferroelectrics SrBi 2 Nb 2 O 9 and Bi 5 Ti 3 FeO 15 , containing two and four perovskite layers, respectively, have been studied using powder neutron diffraction. At temperatures below the ferroelectric Curie temperature both materials crystallize in the polar orthorhombic space group A 2 1 am . On passing through T C , both phases appear to transform directly to a tetragonal paraelectric phase, space group I 4 / m m m . This behavior contrasts with that of the analogs Sr 0.85 Bi 2.1 Ta 2 O 9 and SrBi 4 Ti 4 O 15 , both of which have been shown unambiguously to transform via an intermediate paraelectric orthorhombic phase, space group Amam .

... 近年来, Bi₅FeTi₃O₁₅(BFTO)作为一个很有应用前景的多铁材料受到广泛关注^[9,10] ...

1994

1.534

0.0

Solid State Commun.. 1994, 91(7):567-569

Dielectric and magnetoelectric properties of Bi₅FeTi₃O₁₅.

SINGH R S , BHIMASANKARAM T , KUMAR G S

Ceramic samples of Bi 5 FeTi 3 O 15 were prepared by the solid state reaction method. The samples were characterized by X-ray diffraction. Dielectric measurements were performed from room temperature to 850°C. Magnetoelectric measurements were performed under d.c. fields up to 8 kOe. The results are discussed.

... 近年来, Bi₅FeTi₃O₁₅(BFTO)作为一个很有应用前景的多铁材料受到广泛关注^[9,10] ...

2009

3.794

0.0

Appl. Phys. Lett.. 2009, 95(8):082901-

Multiferroic properties of layer-structured Bi₅Fe_0.5Co_0.5Ti₃O₁₅ ceramics,

MAO XIANG-YU , WANG WEI , CHEN XIAO-BING

Layer-structured, single phase Bi 5 Fe 0.5 Co 0.5 Ti 3 O 15 ceramics was synthesized following a multicalcination procedure. Magnetic moment increases more than three times by substituting half Fe sites by Co ions. The material exhibits an Aurivillius phase with a four-layer unit cell structure, and presents a remarkable coexistence of ferroelectricity and ferromagnetism above room temperature. The measured 2 P r and 2 M r are 13 μ C / cm 2 and 7.8 m emu / g , respectively. The material’s magnetic behavior below 275 ° C is relaxationlike and its magnetic Curie temperature is ∼ 345 ° C .

... 一般认为加强磁性离子之间的相互耦合可以提高材料的铁磁性, 如果采用过渡金属磁性离子掺杂取代BFTO中的Fe³⁺, 有望增强样品内不同磁性离子之间的相互耦合, 从而改善磁性能^[11,12,13] ...

... Mao等^[11]通过Co³⁺对Fe³⁺的取代制备得到Bi₅Fe_{0 ...}

... 其次, 室温下, Pr-1、Pr-2样品的剩余磁量级^[11], 与Yang等^[13]用Nd取代Bi的BNFCT陶瓷的实验结果基本相同(2M_r约0 ...

... Mao等^[11]认为铁磁性可能来源于 Fe-O-Co 的铁磁耦合相互作用 ...

2012

1.486

0.0

J. Mater. Sci.. 2012, 47(6):2960-2965

Influence of different synthesizing steps on the multiferroic properties of Bi₅FeTi₃O₁₅ and Bi₅Fe_0.5Co_0.5Ti₃O₁₅ ceramics.

MAO XIANG-YU , WANG WEI , SUN HUI

The compounds Bi 5 FeTi 3 O 15 (BFTO) and Bi 5 Fe 0.5 Co 0.5 Ti 3 O 15 (BFCT) were prepared by incorporating BiFeO 3 (BFO) and BiFe 0.5 Co 0.5 O 3 (BFCO) into the host Bi 4 Ti 3 O 12 (abbreviated as BFTO-1 and BFCT-1) and by the conventional solid-state reaction method (abbreviated as BFTO-2 and BFCT-2). X-ray analysis indicates a four-layer Aurivillius phases with an orthorhombic symmetry. At room temperature, the remnant polarization (2 P r ) of BFTO-1, BFTO-2, BFCT-1, and BFCT-2 samples are measured to be 11.0, 3.5, 13, and 6.3 μC/cm 2 , respectively, and the corresponding remnant magnetization (2 M r ) are about 2.72 × 10 −3 memu/g, 1.51 × 10 −3 memu/g, 7.6 and 2.1 memu/g, respectively. Both BFTO-1 and BFCT-1 samples exhibit the dielectric peaks at around 755 and 772 °C in their ε – T curves, respectively.

2011

0.0

... Yang等^[13]研究发现, 在Co掺杂的基础上, Bi位掺杂Nd能进一步提高材料的磁性 ...

... 其次, 室温下, Pr-1、Pr-2样品的剩余磁量级^[11], 与Yang等^[13]用Nd取代Bi的BNFCT陶瓷的实验结果基本相同(2M_r约0 ...

... Yang等^[13]则认为这种提升可能是掺杂导致的结构畸变削弱了反铁磁作用所致 ...

2014

1.789

0.0

Ceramics International. 2014, 40(6):7805-7816

Structural, magnetic,vibrational and impedance properties of Pr and Ti codoped BiFeO₃ multiferroic ceramics.

PRAKASH CHANDRA SATI , MANISHA ARORA , SUNIL CHAUHAN

Single-phase (Bi 1− x Pr x )(Fe 1− x Ti x )O 3 ceramics ( x =0.03, 0.06, and 0.10 as BPFT-3, BPFT-6 and BPFT-10, respectively) were synthesized by conventional solid state reaction method. The effect of varying Pr and Ti codoping concentration on the structural, magnetic, dielectric and optical properties of the BPFT ceramics have been investigated. X-ray diffraction indicated pure rhombohedral phase formation for BPFT-3 and BPFT-6 ceramics, however, a structural phase transition from a rhombohedral to an orthorhombic phase has been observed for BPFT-10 ceramic. The maximum remnant magnetization of 0.1824 emu/g has been observed in BPFT-6. With increasing codoping concentration the room temperature dielectric measurements showed enhancement in dielectric properties with reduced dielectric loss. UV–vis diffuse reflectance spectra demonstrated the strong absorption of light in the visible region for a band gap variation 2.31–2.34 eV. Infrared spectroscopy indicated the shifting of Bi/Pr–O and Fe/Ti–O bonds vibrations and change in Fe/Ti–O bond lengths. Decrease in the conductivity on increasing Pr and Ti concentration in BFO is attributed to an enhancement in the barrier properties leading to suppression of lattice conduction path arising due to lattice distortion as confirmed from impedance analysis.

... 同时Pr离子具有+3、+4两种价态, 可以抑制氧空位, 改善漏电流, 降低介电损耗, 提高材料介电性能^[14] ...

2010

2.39

0.0

Journal of Alloys and Compounds. 2010, 501(2):L29-L32

Structural, dielectric and magnetic properties of Pr substituted Bi₁-_xPr_xFeO₃(0#cod#x02264;x#cod#x02264;0.15) multiferroic compounds.

NEERAJ KUMARA , NEERAJ PANWARB , BHASKER GAHTORIA

Here we report the structural, dielectric, electric polarization and magnetic properties of Bi 1− x Pr x FeO 3 (0 ≤ x ≤ 0.15) ceramic compounds. The samples have been synthesized by conventional solid state reaction method at 815 °C and it was observed that they crystallize in the rhombohedral structure. Rietveld refinement was carried out with two possible space groups viz. R 3 C and P 1. With an increase in Pr content the dielectric constant increases, whereas the dielectric loss decreases. Pristine and substituted BiFeO 3 compounds exhibited substantial ferroelectric polarization at room temperature. An optimum or saturation like scenario was noticed with x = 0.12 sample. Isothermal magnetization (M-H) plots of pristine BiFeO 3 indicated weak ferromagnetic (FM) character presumably due to the presence of minute Bi 25 FeO 39 secondary phase. It is also observed that the magnetic Neel temperature ( T N ) increases with increasing Pr content. Interestingly, with Pr substitution at Bi-site the impurity phase tends to disappear and the antiferromagnetic (AFM) nature appears at 300 K.

... 另外, Pr³⁺、Pr⁴⁺离子半径不同, 可能诱导结构相变, 进一步提高BFTO多铁性能^[15] ...

2008

1.534

0.0

Solid State Communications. 2008, 147(5/6):186-189

Electrical and magnetic properties of Bi₅FeTi₃O₁₅ compound prepared by inserting BiFeO₃ into Bi₄Ti₃O₁₂.

MAO X Y , WANG W , CHEN X B.

A novel four-layer Bi 5 FeTi 3 O 15 (BFTO) compound was synthesized via sintering the mixture of Fe 2 O 3 , Bi 2 O 3 oxides and already-prepared Bi 4 Ti 3 O 12 powders. At room temperature, the remnant polarization (2 P r ) ( 2 P r ) and the coercive field (2 E c ) ( 2 E c ) of Bi 5 FeTi 3 O 15 samples were about 11.8 μC/cm 2 and 270 kV/cm, respectively. The BFTO samples show a weak ferromagnetism with M r ≈ 1.36 × 1 0 − 6 emu / g . A sharp dielectric peak was found, showing that the arrangement of iron ions in each crystal unit may be relatively in order. Two peaks were found in the tanδ−T tan δ − T curves. The peak at lower temperature (∼400 ∘ C) behaves relaxation characteristic, with the activation energy (H) ( H ) of about 1.62 eV and the upper peak is frequency independent.

... 7 Am²/kg的2M_r高5个数量级^[16], 比BFCTO陶瓷7 ...

2008

0.0

J. Appl. Phys.. 2008, 103(9):094101-

Magnetocapacitance of polycrystalline Bi₅FeTi₃O₁₅ prepared by Sol-Gel Method.

DONG X W , WANG K F , WAN J G

Bi 5 Ti 3 Fe O 15 bulk ceramic and thin film samples are prepared using the sol-gel method. The dielectric, ferroelectric, and magnetic behaviors of these samples are measured in order to investigate the possible multiferroiceffect. The superparamagnetic behavior with dominant antiferromagnetic(AFM) interaction background for the as-prepared Bi 5 Ti 3 Fe O 15 samples is revealed. The clearly identified magnetocapacitance effect at low temperature is argued to originate from the suppression of the AFM interaction by external magnetic field.