引用本文
张发强, 李永祥. 铋层状结构铁电体的研究进展. 无机材料学报, 2014, 29(5): 449-460ZHANG Fa-Qiang, LI Yong-Xiang. Recent Progress on Bismuth Layer-structured Ferroelectrics. Journal of Inorganic Materials, 2014, 29(5): 449-460
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铋层状结构铁电体的研究进展
张发强1,2, 李永祥1
1. 中国科学院 上海硅酸盐研究所, 信息功能材料与器件研究中心, 上海 200050
2. 中国科学院大学, 北京100049
通讯作者：李永祥, 研究员. E-mail:yxli@mail.sic.ac.cn
作者简介：张发强(1986-), 男, 博士研究生. E-mail:zhangfq@student.sic.ac.cn
基金:国家自然科学基金重点项目(50932007);国际科技部973项目(2009CB613305);
摘要
铋层状结构铁电体 (BLSF) 作为一种类钙钛矿无铅铁电压电材料, 由于其在高温、高频以及非易失性铁电随机存储器等领域具有突出的综合优势, 因而受到广泛关注。本文以BLSF的综合特征为基础, 对其结构设计和微结构研究中存在的问题进行了详细探讨, 并重点总结了近二十年来其在性能优化和薄膜制备中取得的进展。此外, 本文还对一些以铁电为背景的新的研究方向做了介绍。最后提出了BLSF在未来发展中值得关注的几个重要问题。
关键词:
铋层状结构; 铁电体; 无铅压电陶瓷; 非易失性铁电随机存储器; 综述
中图分类号:TQ174
文献标志码:A
文章编号:1000-324X(2014)05-0449-12
Recent Progress on Bismuth Layer-structured Ferroelectrics
ZHANG Fa-Qiang1,2, LI Yong-Xiang1
1. The Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
Fund:National Natural Science Foundation of China (50932007);The Ministry of Science and Technology Project 973(2009CB613305);
Abstract
As an improtant lead-free ferroelectric/piezoelectric system, the past few decades have attracted increasing attention of bismuth layer structured-ferroelectrics (BLSF) due to its comprehensive advantages in the areas of high temperature, high frequency and ferroelectric random access memory (FRAM). In this paper, the recent progresses on the study of this system were reviewed. Firstly, as the basic of other researches, the key issues in strucutre design and microstructure study were dicussed in detail. Then special emphasis was put on ferroelectric/ piezoelectric performance and film technology. Additionally, some new research fields that were closely related to ferroelectric were introduced. In the end, the research directions were also extracted according to the authors’ knowledge.
Keyword:
bismuth layered structure; ferroelectric; lead-free piezoelectric; ferroelectric random access memory; review
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0 引言铁电材料作为一类重要的信息功能材料, 同时具有压电效应、热释电效应和电光效应等, 在众多领域具有重要的应用。含氧八面体结构作为铁电材料中最大, 也是最重要的一个家族, 可以按其氧八面体的排列方式分为钙钛矿型、铌酸锂型、钨青铜型、焦绿石型和铋层状型等五类。相比而言, 对钨青铜型、焦绿石型以及含铋层状化合物型的非钙钛矿结构或类钙钛矿结构的功能器件的研究与应用比较少, 这主要是由于类钙钛矿结构的组成和晶体结构的复杂性, 但是这类材料大多无毒性, 且具有特殊的性能和特定的应用, 因此仍是不容忽视的重要材料体系。
铋层状结构由Aurivillius等[1,2,3]于1949年发现, 因此又称为Aurivillius相, 截至上世纪70年代该族被发现的化合物已超过50种[4]。从结构上看, 铋层状材料的价带由Bi6s和O2p轨道杂化而成, 这种强的相互作用降低了结构的对称性, 并以偶极子的形式表现出来, 从而引起了一些与偶极子密切相关的性能, 包括铁电、压电和非线性光学性能等[5], 也使其作为光催化材料时具有较高的氧化活性和电荷流动性[6,7]。同时, 铋层状材料结构中本征及非本征氧空位的存在又促使其具有优异的氧离子导电性[8], 这是固态离子导电领域的一大研究对象。
在铋层状结构材料的诸多性能中, 铁电压电性能是最受关注的一个方向。如表1所示, 相比包括钙钛矿结构在内的其它体系, BLSF在各类压电传感器应用中表现出明显的综合优势, 这种高居里温度、低介电常数、低老化率、高击穿场强、高机械品质因数和优异的谐振频率稳定性使其在高温、高频以及信息存储领域有着重要的应用前景[9,10,11]。本文试图从结构、性能及近来研究动向三个角度综述铋层状结构铁电体的相关研究与进展, 希望能为今后的研究提供一定的借鉴。
1 结构设计与微结构研究1.1 晶体结构如图1所示, BLSF的结构由类萤石结构的(Bi2O2)2+层(铋氧层)和(A m-1B mO3 m+1)2-层(类钙钛矿层)沿 c轴方向交替排列而成。结构中A位为适合12配位的一、二、三、四价阳离子, 如K+、Na+、Ca2+、Sr2+、Pb2+、Ba2+、Ln3+、Bi3+、Ce4+等, B位为适合6配位的三、四、五、六价阳离子, 如Fe3+、Cr3+、Ti4+、Nb5+、Ta5+、W6+、Mo6+等; 除一些不常用的表达外, m通常为一整数, 代表了类钙钛矿层中氧八面体的层数, 据推测 m不大于12~13, 当 m大于8时, 已很难获得BLSF纯相[12]。就结构而言, BLSF本身属于一类共生结构[13], 是众多共生结构中的一个经典体系, 但通常在BLSF家族中共生结构则专指一类特殊的超晶格结构, 如图1, 这种结构基本都以 m值相邻的BLSF单层为基元沿c轴方向交替排列而成, 按照晶体结构中出现的钙钛矿层数, 这种化合物可以表示为 m+ n结构, 也有少数学者表示为( m+ n)/2结构。
1.2 铋层状结构—— 一类典型的钙钛矿衍生结构如图2所示[13], 通常BLSF和Dion-Jacobson相(DJ phase)、Ruddlesden-Popper相(RP phase)同属于钙钛矿结构的层状衍生结构, 它们之间有着类似的特征, 都可以看成在钙钛矿结构中沿 c方向周期性的插入了某种结构, DJ相插入了一层碱金属或碱土金属阳离子, RP相插入了两层碱金属阳离子, 而BLSF则插入了一层(Bi2O2)2+层。这种类钙钛矿的特征决定了BLSF的研究中大量存在着钙钛矿影子, 如结构设计、稳定性讨论以及第一性原理中模型的建立等。
研究显示, 在这三种相中, 除了钙钛矿层天然的可设计性外, 钙钛矿层之间的插层结构同样具有一定的可操作性。一方面, RP相(图2c)和DJ相(图2g)中的插层阳离子可以在硝酸盐熔盐中被离子半径更小的碱金属阳离子所取代。这种特性使得BLSF与DJ相、RP相之间乃至与钙钛矿之间具备相互转换的能力, 其重要意义在后面讨论织构化时能够看到。而另一方面, 这三种结构中的插层离子也可以被H+取代, 转变为准RP相(图2d)和准DJ(图2f)相, 在溶液中表面活性剂的作用下, 这两种结构会分解出各自钙钛矿层(图2k), 即二维钙钛矿层状纳米结构, 这一特点既对最大限度地开发这类材料的性能有重要意义, 也对人工设计新型钙钛矿超结构有深远影响。
1.3 BLSF的结构限制在BLSF的研究中, 固溶、掺杂以及新结构设计等作为性能调控的重要手段被广泛采用, 但和其它材料一样, 这种调控必然受到材料本征特性的限制。作为一种类钙钛矿结构, BLSF的结构研究沿用了容差因子( t)的概念, 但对其结构的调控不仅需要考虑钙钛矿层作为独立单元的稳定性, 在很大程度上还需要考虑钙钛矿层与(Bi2O2)2+层之间的匹配问题, 因此变得更为复杂。
表1Table 1表1(Table 1) 表1 各类压电材料性能对比 Table 1 Parameters relevant to sensor applications for various piezoelectric materialsMaterialsSensitivityResistivity QMTemperature stabilityMax use temp./℃AgingPerovskiteHighLow-mid20-2000Low<< TCYesBLSFMediumMedium500-8000Medium<< TCLowPLS*LowHigh-High<< TCLowLiNbO3MediumLow1000-3000Medium<500Lowα-SiO2LowHighHighHigh~300N/ATourmalineLowHighHighHigh~900N/ALi2B4O7LowLow-Medium~500N/AAlN/GaNLowHigh-High~700N/A*PLS — Perovskite layer structure
表1 各类压电材料性能对比 Table 1 Parameters relevant to sensor applications for various piezoelectric materials
图1Fig. 1Figure OptionViewDownloadNew Window 图1 铋层状及共生铋层状结构模型Fig. 1 Structural models of bismuth-layered structure and corres--po--nding intergrowth structure
Armstrong等[14]收集了大量钙钛矿结构的晶格参数并总结出计算理想钙钛矿MRO3点阵常数 ap的经验公式:
Å (1)
式中, rR、 rM分别代表六配位和八配位阳离子的半径。对比理想的(Bi2O2)2+层的点阵常数, 发现钙钛矿层和(Bi2O2)2+层之间确实存在失配以及相互的弛豫。
对钙钛矿层稳定性的讨论, 主要借助于容差因子( t)。在纯钙钛矿ABO3型结构中, 若以 rA、 rB和 rO分别代表A离子、B离子以及氧离子的半径, 则容差因子 t表示为:
(2)
当 t值在0.77~1.10时, 钙钛矿结构都很稳定[15]。但对于BLSF而言, 由于类钙钛矿层与(Bi2O2)2+层是共生的, 两者间横向尺寸的失配必然引起各自结构的失稳, 从而限制容差因子的取值范围。Subbarao[16]研究发现, 当 m=2、4和5时, t值范围分别为0.81~ 0.93、0.85~0.89和0.86~0.87。也就是说, 随着 m增大, 容差因子 t取值范围不断缩小。
图2Fig. 2Figure OptionViewDownloadNew Window 图2 各层状钙钛矿材料结构模型及其相互转换规律[13]Fig. 2 Ion-exchange and intercalation reactions of layered perovskites that involve discrete interlayer cations[13]
对钙钛矿层与(Bi2O2)2+层之间失配问题的研究主要借用了弹性应变能的概念。弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功。基于弹性模式, Kikuchi等[20]给出了BLSF中在 a- b面内失配应变能的计算公式:
其中 a、 aB′、 aP′为已知晶格参数, VB′为未受约束的(Bi2O2)2+层的单胞体积。计算表明在特定组分的BLSF系统中, m值的增加将提高体积差变(Δ V)和应变能( E), 从而降低结构稳定性低。
就目前的研究来看, 可以认为只要满足钙钛矿层中离子堆积的几何规则以及层间链接的弹性应变条件, m值从1到无穷大( m=∞, 对应纯的钙钛矿结构)都是可能的[22]。然而, 目前实际发现的化合物对应的 m值一般为1~5。Kikuchi等[20]曾试图在Pb系和Na系中分别合成 m>7和 m>5的化合物, 但均未成功。而其它一些体系, 如Bi4Ti3O12-BiFeO3[23,24]虽然能制备出 m值达9的结构, 但当 m>5时已很难获得纯相, 而且其热稳定性相对 m≤5的结构会明显降低。这些现象的存在说明仍然存在某些尚不明确的机制制约着 m值进一步增大, 有待进一步的研究。
1.4 铋层状结构中的晶格缺陷与有序-无序问题随着上世纪60、70年代透射电镜的迅速发展, 透射电镜很快被应用到BLSF的结构研究中。人们在BLSF中观察到了各种形式的缺陷, 它们的存在既和前述的结构稳定性问题紧密联系, 也为人们认识和设计BLSF提出了新的思路。
Hutchison等[27,28]在Ba2Bi4Ti5O18( m=5)中频繁地观察到所谓超位错(super-dislocation)的存在, 这种超位错由局部多插入一层氧八面体引起, 会在晶粒内导致连锁错位, 表现为大量台阶缺陷, Hutchison认为这些现象的产生同(Bi2O2)2+层与类钙钛矿层之间晶格失配有关。另外, 如图3(a), Zhou等[25,29]在一系列Bi-W-Nb-O结构中观察到规律分布的台阶缺陷(step-like defects), 并指出这种缺陷的形成是由于类钙钛矿层中B位原子Nb5+/W6+取代破坏了局部电荷平衡进而引起的结构变化。
与位错相伴, 层错也是BLSF中一种普遍存在的缺陷。确切地说, BLSF中的层错也是一种超层错, 是结构中错排的BLSF单层。事实上, 正如Ding等[26]在SrBi2Ta2O9( m=2)中观察到的(图3(b)), 一定程度上也可将超位错看成是没有贯穿的层错, 由于层错的 m值与基体的 m值不相等, 于是在晶粒内导致一连串的位错或台阶(图3(c))。
图3Fig. 3Figure OptionViewDownloadNew Window 图3 Bi8W2Nb2O23晶粒中规律分布的超位错(a)[25]和SrBi2Ta2O9晶粒中未贯穿的超层错及其引起的系列台阶缺陷(b, c)[26]Fig. 3 HRTEM image of the Bi8W2Nb2O23 grain with regularly distributed super-dislocations(a)[25] and HRTEM images of a broken super-stacking fault and the caused step-like faults in SrBi2Ta2O9 grain(b, c)[26]
就现象而言, 那些 m值对成分比较敏感的体系更容易观察到层错和台阶。Hutchison等[27]在 m=8的Bi9Ti3Fe5O27结构中就观察到了 m=4和 m=5的层错, 而 m=5的Ba2Bi4Ti5O18中观察到大量的台阶必然也和层错的存在有关。除了这类 m值比较大的普通铋层状结构外, 共生铋层状结构也是层错和台阶频发的一类体系。Kobayashi等[30,31]在Bi4Ti3O12- BaBi4Ti4O15(BiT-BBTi, m=3+4)单晶中观察到局部多插入BiT层形成的层错。如图4, Gao等[32]在Bi3TiNbO9-Bi4Ti3O12(BTN-BiT, m=2+3)陶瓷频繁的观察到各种形式的BTN、BiT型层错, 并发现低温样品中的层错会明显高于高温样品。同时, 他们研究还发现BiT型层错中存在Nd的固溶, 暗示了层错与成分的密切关系[33]。
从本质上讲, 层错的形成原因仍然难以回答。基体中层错含量的增加会使其结构变得复杂, 当层错增加到一定程度时甚至无法定义结构本身。如图4所示, 层错间时有时无的相对位置关系更将其本质变得格外混乱。事实上, 从Rao等[34,35]关于共生结构的综述可以看出, 层错本身是贯穿各共生体系的一个重要现象, 它的存在引出了共生体系中有序-无序的问题。一方面在那些能形成长程有序共生结构的体系仍会出现无序结构, 另一方面在所谓的无序共生结构中也能频繁地在局部观察到几个周期的有序。这些现象的存在既与前述的结构稳定性问题相联系, 同时也衍生出一些新的问题, 比如: 重复多少个周期可以认定为一个相？所谓的无序共生结构该如何理解？其形成原因是什么？热力学还是动力学？其对性能有何影响？
图4Fig. 4Figure OptionViewDownloadNew Window 图4 Bi3TiNbO9-Bi4Ti3O12(BTN-BiT, 2+3)晶粒中的BTN型层错以及由此引起的新的堆垛周期[32]Fig. 4 HRTEM image of BTN stacking faults in BTN-BiT grain and the caused new orderings[32]
2 铋层状材料的铁电压电性能2.1 对称性与自发极化BLSF在居里点以上为四方顺电相, 空间群为I4/mmm; 在居里点以下, 绝大多数为正交相, 且当 m为奇数时空间群为B2cb, 为偶数时空间群为A21am[4]。Bi4Ti3O12作为一个特例, 在低温下为单斜相, 对应空间群为m[36,37]。从对称性角度讲, BLSF这种非中心对称的结构特征决定了其铁电压电性。
就价键理论中离子特性而言[38], 在孤对电子的影响下, Bi3+离子与O2-离子成键时会表现出明显的各向异性, 从而造成结构的畸变。同时, 过渡金属离子的d0或d1电子会使得离子同周围O2-离子以非对称的方式进行成键, 在这两个因素的作用下结构中正负电荷中心不再重合, 从而表现出极性。如图5, 以Bi3TiNbO9为例, 其结构畸变中存在平行于(001)和(100)面的原子运动[22]:
1) Nb、Ti原子沿 a轴偏离氧八面体中心, 同时氧八面体绕着 c轴旋转以满足Bi(1)成键, 这导致 a、 b参数的减小和正交畸变( b< a)的发生。
2) 同样为了满足Bi3+的成键要求, 氧八面体绕 a轴旋转, 这一旋转会因Bi(2)-O(2)键的作用而进一步增强, 同时这也导致了O(2)的过价(over-bonding), 为了抵消这一作用氧八面体会在 c方向被拉长, 最终导致 c轴的变长。
图5Fig. 5Figure OptionViewDownloadNew Window 图5 Bi3TiNbO9沿<100>方向的投影图[22]Fig. 5 Projection of Bi3TiNbO9 along <100> direction[22]
BLSF是一种典型的位移型铁电体, 目前研究显示其自发极化主要来自三部分贡献: I) B位离子的移动; II) 氧八面体沿 c轴倾侧; III) 氧八面体在 a- b面内的旋转。
而各离子对极化的作用, 可以通过结构中每个离子相对顺电相的偏移量来计算, 公式如下[39,40]:
(4)
其中 m i是各位重复度, 为原子相对于顺电相的偏移量, Q i e为第 i种离子的电荷数, V是单胞体积。通过计算发现, 不同体系极化产生根源的不同, 如CaBi2Ta2O9结构氧八面体中的O(5)2-离子的偏移对自发极化的贡献很大; 而在SrBi2Ta2O9结构中, (Bi2O2)2+中的Bi3+也对极化有很大的贡献[40]。
2.2 性能及其优化BLSF虽然有许多优势, 但也存在着剩余极化小、压电活性低、矫顽场大以及高温介电损耗高等缺点, 使其应用受到一定的限制。为了提高其性能, 人们进行了大量探索并积累了丰富的经验。目前常用的方法包括掺杂改性、构筑共生结构以及织构化等。
2.2.1 掺杂改性
掺杂取代是BLSF最常用的改性方法之一。早期的研究表明, BLSF的居里温度( Tc)与类钙钛矿层中A位离子有关: A位离子半径越小或电负性越大, 居里温度越高[41]。但压电活性受取代离子半径、电负性等多重因素影响, 关系较为复杂[42,43]。
A位掺杂在BLSF改性的报道近年来层出不穷, 镧系元素是最常用的掺杂取代离子[39,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]。镧系元素可以不同程度地提高Bi4Ti3O12的铁电性, 并且对其疲劳特性的改善亦有明显效果[44,45]。一般研究认为是类钙钛矿层中A位的Bi3+被取代, 减少了高温下由于铋的挥发而产生氧空位的几率。另外, Chon等[45]通过解析Nd3+掺杂的BiT的晶体结构, 发现Nd3+掺杂使Ti4+的偏移方向发生了变化, 即自发极化主要沿 c轴分布。Yau等[61]通过Raman光谱在掺La3+的BiT中也得到了类似结论。
B位掺杂在 m=2、3层的铋层状化合物中也得到广泛研究[62,63]。对未掺杂BiT研究表明其容易产生氧空位[64], 且为p型半导体[65], 其漏电流相对较大, 对极化不利。采用B位施主元素掺杂可以有效提高BiT电阻率[66,67,68,69,70], 从而提高其铁电压电性能。
对A、B位复合掺杂也有较多研究[71,72,73,74,75]。Takayuki等[74]通过La3+, Nd3+与V5+复合掺杂, 发现复合掺杂后的薄膜相对于未掺杂或者单一元素掺杂的薄膜具有更高的剩余极化。因此, 他们提出了位置工程(site engineering)的概念, 认为A位离子掺杂降低材料的居里温度至沉积温度以下, B位掺杂能解钉扎, 因此, A、B位复合掺杂可以有效提高薄膜的铁电性能。另外有人通过对铋层状陶瓷的A、B位同时掺杂取代, 得到了高压电活性和较高 Tc的材料[71]。
2.2.2 构筑共生结构
如前所述, 不同层数的BLSF可以沿 c轴交替排列形成一种超晶格结构, 利用这两种不同结构单元之间的相互作用, 能够提高BLSF的铁电性能[30-31, 76,77]。如Noguchi等[76]首先报道了Bi4Ti3O12-SrBi4Ti4O15共生铁电陶瓷的剩余极化为15 µC/cm2, 高于在同样工艺条件下制备的Bi4Ti3O12和SrBi4Ti4O15。Kobayashi等[30,31]对比研究了BiT、BaBi4Ti4O15(BaBT)和BiT-BaBT, 发现无论是陶瓷还是单晶, BiT-BaBT的剩余极化都要比BiT和BaBT大, 且单晶BiT-BaBT沿 a( b)方向的剩余极化达到了52 µC/cm2。从结构出发, Yi等[77]对比分析了Bi3TiNbO9-Bi4Ti3O12、Bi3TiNbO9和Bi4Ti3O12结构中氧八面体的旋转方式, 发现沿 a- c面相对 c轴的倾角α x的增加对共生结构的铁电性有重要贡献, 虽然BTN-BiT的自发极化低于BiT, 但相对BTN大的自发极化特别是比BiT更容易进行的畴反转行为使得BTN-BiT陶瓷表现出比BTN和BiT要大的剩余极化。
2.2.3 织构化
受对称性的影响, BLSF的晶粒通常呈片状, 其电学性能亦具有极为明显的各向异性, 自发极化主要位于 a- b面内。晶粒方向随机分布的陶瓷难以最大限度地利用其性能, 因此织构化技术被引入到BLSF的改性中。常采用的织构化方法可简单分为两类: 一类是基于热、力、电、磁场的热锻/压、SPS、磁定向等方法[78,79,80,81,82,83]; 一类是基于原料形状的模板法[84,85,86,87,88,89]。
Takenaka等[78,79]采用热压处理得到明显织构的BiT陶瓷, 其垂直于织构化方向的 Pr达37 μC/cm2, 远大于普通BiT陶瓷的9.3 μC/cm2。在热压基础上, Fuierer等[80]将电场引入到BiT陶瓷的织构化过程中, 发现在电场作用下陶瓷实现了三个方向的织构, 表现出类似单晶体的性能特征。Shen等[81]则巧妙地利用纳米陶瓷颗粒在脉冲电场/电流下超塑性变形这一特性, 采用SPS实现了BiT陶瓷的织构化, 其 Pr达27 μC/cm2。除此之外, Chen等[82,83]对强磁场处理过的BiT陶瓷织构化行为进行了研究, 发现在灌浆成型时毛细管力的作用下, 样品上表面到下表面逐渐表现出不同的织构特性, 且这种影响随初始晶粒形状的变化而变化。
模板法制备织构化BLSF陶瓷也是一种常用方法。Duran等[86]以片状KSr2Nb5O15为模板, 采用流延-叠层的方法制备出织构化的Sr0.9Nd0.1Bi2Nb2O9陶瓷, 其 Pr达20.3 μC/cm2, d33最高达84 pC/N。Takeuchi等[84,85]则采用反应模板法, 以片状BiT为模板, 利用BiT与Bi2O3、CaCO3、TiO2和Na2CO3的反应获得了织构化的CaBi4Ti4O15和Na0.475Ca0.05Bi0.4475Ti4O15陶瓷, 对比普通陶瓷, 前者的 d33增加了200%, 达到45 pC/N, 后者则增加了238%, 达到44 pC/N。
值得一提的是, BLSF在其它一些钙钛矿及类钙钛矿陶瓷的织构化中也有重要应用。2004年Saito等[90]以片状NaNbO3为模板, 制备出 d33达416 pC/N的(K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3织构化陶瓷, 这一结果作为铌酸盐体系压电性能研究的一个重大突破, 一度吸引了大量学者关注[91]。在这一研究中, Bi2.5Na3.5Nb5O18( m=5)作为前驱体在熔盐法制备片状NaNbO3模板的过程中起到了不可取代的作用[92]。相关研究显示[93], 这一方法也适合于制备片状的Na0.5Bi0.5TiO3模板。此外, 直接以片状的铋层状粉体为反应模板也是常用的方法, Wu等[94]以BiT为模板制备出了织构化的(Na0.5Bi0.5)0.94Ba0.06TiO3陶瓷。
3 BLSF铁电薄膜BLSF薄膜的研究最早始于上世纪70年代初, Takei等[95]采用二极反应溅射法分别在Pt和MgO衬底上制备出BiT薄膜。Wu和Sugibuchi等[96,97]先后将BiT薄膜应用于铁电场效应晶体管(Field Effect Transistor, FET), 在硅基片上制备出可循环读写105次而不表现出疲劳的FET, 并发现其具有低的开路电压以及优异的集成电路兼容性, 因而认为BiT在只读存储器领域有着重要的应用前景。然而由于种种原因, 这一结果在之后的20年间并没有得到足够的重视, 直到上世纪1995年, De Araujo等[98]在Nature期刊上发表了一篇关于非易失性铁电存储器的文章, 报道SrBi2Ta2O9(SBT)和BaBi2Ta2O9(BBT)薄膜经1012次读写仍不表现疲劳, 同时其漏电流低于相同条件下PZT薄膜的百分之一, 这一结果从此在铋层状铁电薄膜乃至陶瓷领域中掀起了一股以非易失性铁电存储器为背景的研究热潮, 并取得了大量成果。
在材料体系上, 1999年Park等[44]首先报道了剩余极化达12 μC/cm2且经3×1010循环读写之后仍不出现疲劳的Bi3.25La0.75Ti3O12(BLT)薄膜。之后, 2002年同样是在BiT体系上, Chon等[45]通过Nd掺杂制备出 Pr达51.5 μC/cm2, 且经6.5×1010循环读写之后仍不出现疲劳的Bi3.25Nd0.75Ti3O12(BNT)薄膜, 从而为BLSF在非易失性铁电存储器领域中的应用奠定了基础。
在机制上, 如何解释BLSF这种优异的抗疲劳性从一开始就受到了广泛关注。Ding等[99,100,101]分别在抗疲劳性能优异的SBT和BLT晶粒中观察到了大量反相畴界(APB), 并通过原位观察发现这些反相畴有助于极化反转时在薄膜内部诱发新畴的形核, 能够有效地减轻电极附近区域的形核负担, 从而降低这一区域的过早疲劳, 因此认为APB的存在是铋层状铁电薄膜优异的抗疲劳性的根源。此外, Su等[102]发现90°畴密度较高的材料对应的疲劳性好, 他们认为90°畴在极化过程中会吸收电荷缺陷, 90°畴密度低的材料其畴壁很快被钉扎, 从而影响到抗疲劳性能。
薄膜制备上, BLSF晶粒通常为 c轴取向或随机取向, 这既对薄膜的极化性能不利, 也对纳米尺度下记忆单元间极化特性的一致不利, 因此制备一致的非 c轴取向, 特别是具有 a( b)轴取向的薄膜显得尤为重要。虽然大量文献[102-107]报道了类似(118)、(104)取向的BLT薄膜和(116)、(103)取向的SBT薄膜, 但具有 a( b)轴取向的薄膜则相对少见。Moon等[108]报道具有 a( b)轴取向的SBT薄膜, 但这一薄膜并非生长在电极材料之上, 因此不具备实用性。此后, Lee等[109]以SrRuO3为底电极, 在Y稳定的ZrO衬底上成功制备出了具有 a( b)轴取向的BLT薄膜(图6), 从而攻克了这一难题。
4 BLSF的拓展性研究在传统铁电压电性能研究的同时, 近年来在BLSF的研究中出现了一些与其铁电压电性相关的新的研究方向, 包括以多铁为背景的磁-电性能研究以及以太阳能电池为背景的铁电光伏特性研究。
多铁性研究主要集中在以Bi5Ti3FeO15 (BTF, m=4)结构为基的体系上, 由于Fe3+-O-Fe3+负的超交换作用, 因而BTF理论上表现出反铁磁性。Mao等[110]报道BTF陶瓷的 Pr=5.9 μC/cm2, 并发现其表现出弱的铁磁性, 认为结构中少量的Fe2+离子是导致这一现象的根本原因。利用Co3+-O-Fe3+间正的交互作用, Mao、Hu和Wang等分别[111,112,113]对Co掺杂BTF (BFCT) 陶瓷的磁-电性能进行了研究, 均发现Co掺杂可以将剩余磁化强度提高3个数量级, 并能在一定范围内增加材料剩余极化。而Sun等[114]对Bi5Fe0.5Co0.5Ti3O15薄膜的研究显示, 其 Pr=15.8 μC/cm2, Mr=2.6 emu/cm3, 且观察到了磁介电效应, 0.6 T/ 100 kHz下对应MDC=0.39%。在Co掺杂的基础上, Yang和Mao等分别[115,116]对稀土Nd、La掺杂BFCT(BNFCT, BLFCT)薄膜的磁-电性能进行了报道, BNFCT薄膜的 Mr=165 memu/g, Yang等[115]认为如此大的剩余磁化强度可能和小半径的Nd3+和Co3+离子的取代有关, 但仍需进一步研究。BLFCT薄膜的 Mr=25.6 memu/g, Pr=7.7 μC/cm2, 且在室温下表现出明显的磁介电效应, 1 T/1 kHz下MDC=8.1%, 远远大于BFCT薄膜。从这些结果可以看出, BLSF在多铁领域有着重要的应用前景, 但目前还处于起步阶段, 大量工作有待开展。
图6Fig. 6Figure OptionViewDownloadNew Window 图6 c-轴取向Bi3.25La0.75Ti3O12(BLT)多晶薄膜AFM形貌照片(a)和BLT晶粒<010>方向高分辨像(b)[109]Fig. 6 AFM topography image of BLT film (a) and HRTEM image of the BLT grain along <010> direction (b)[109]
铁电光伏效应是光生电子-空穴在铁电体内电场作用下发生分离形成稳定光生电流或开路电压的现象, 这一现象在上世纪70年代被发现[118], 由于铁电体内电场比p-n节内建电场大一个数量级, 且作为一种特殊体效应其光伏电压比p-n结光伏电池高2~4个数量级, 达103~105V/cm, 近年来受到广泛关注[119,120,121,122,123]。但受其较大禁带宽度的影响, 铁电体内部电子-空穴处于紧束缚状态很容易发生复合, 体电导很低, 光伏效应一直比较差, 因此设计具有窄禁带宽度的铁电体成为一个研究重点。近年来, BLSF在这方面的应用开始受到关注, Choi等[124]对LaTMO3(TM=Al、Ti、V、Cr、Mn、Co、Ni)系列掺杂Bi4Ti3O12薄膜的禁带宽度进行了研究, 发现LaCoO3掺杂产生显著作用, 能够将禁带宽度降低近1 eV。如图7显示[117], LaCoO3掺杂时La部分取代了 (Bi2O2)2+中一侧的Bi, 采用第一性原理计算发现禁带宽度的减小是Co填充O空位附近的B位后引起周围Bi离子6p轨道能态降低的结果, 而对薄膜光电导性能的测试也表明铋层状结构是一类值得进一步开发的光电子材料。
总体而言, 无论是多铁研究还是铁电光伏特性的研究本质上都需要克服相同的矛盾, 即磁性/体电导的提高以及铁电性的保留, 这就要求在材料设计中必须充分考虑到这一矛盾, BLSF作为这两个领域开发较晚的材料体系, 应该在充分利用其结构优势的同时引入其它体系中较为成熟的理论, 这样才能实现更合理的设计。
图7Fig. 7Figure OptionViewDownloadNew Window 图7 Bi4Ti3O12(BiT)、Bi4Ti3O12-2CoLaO3(1B2L)原子分辨率Z衬度像以及1B2L局部EELS面扫(a)和第一性原理计算BiT及Co掺杂BiT结构电子态密度(b)[117]Fig. 7 Atomic resolution Z-contrast STEM images of BiT and 1B2L. The elemental maps of 1B2L for Ti and La visualized by EELS are also shown(a) and the caculated electronic density of states for BiT and Co-doped BiT structure(b)[117]
5 总结与展望本文简要介绍了BLSF的研究背景和研究内容, 从结构、性能及研究动态三个方面构建了BLSF的研究框架, 并详细分析了各方向的进展以及遗留问题。我们认为BLSF至少在以下几方面还有待进一步的研究:
1) 结构的认识和新结构的设计。结构是一切研究的基础, 随着研究的积累, 对铋层状结构的认识不断深入, 但其结构稳定性问题仍是一个核心问题。随着 m值的增大, 铋层状结构特别是其共生结构的超晶格有望逐渐表现出纳米异质结的某些特点[12], 这在一定程度上促使了一些新结构的诞生, 但受结构稳定性的影响, 相关的设计并不十分顺利。同时, 有序-无序一直都是铋层状结构乃至其它共生体系中一个普遍的现象[34,35], 但却未得到很好的解释, 对这个问题的研究既有利于加深对结构或物相的认识, 也有利于新结构的设计。
2) 铁电薄膜关键问题的突破。虽然BLSF铁电薄膜在诸多方面表现出了相对优异的性能, 但仍存在一些问题和技术障碍, 包括较高的制备加工温度、仍需解决的疲劳和老化问题以及有待深入研究的相关物理问题等等[125]。
3) 性能裁剪。就结构而言, 铋层状结构特别是其共生结构有着天然的可裁剪性, 这对材料的多功能化有着重要的意义, 但这一特质到目前为止尚未得到很好利用。BLSF在多铁及铁电光伏特性中的应用可以说是不同应用领域交叉的产物, 从这两个研究方向面临的问题来说, 如何在借鉴成熟的理论方法的同时充分利用铋层状结构的优势(如可裁剪性)是一个值得考虑的问题; 而就方法而言, 将BLSF的铁电性进一步拓展到其它的领域中有可能获得意想不到的效果。
4) 第一性原理计算的应用。第一性原理计算是揭示组成-构-性能之间内在联系的一种有效方法, 可以应用于前述三个方面的研究, 帮助人们理解一些现象的本质[126], 甚至实现真正意义上的材料设计。由于BLSF十分复杂, 单胞原子数大多几十甚至远远超过一百, 计算量很大, 因此第一性原理在BLSF中的应用并不普遍。但随着信息技术的迅猛发展, 这种方法也越来越多的被用于BLSF的研究, 相信在不久的将来其必定能在BLSF的研究中发挥更加突出的作用。
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1
1950
0.0
0.0
... 铋层状结构由Aurivillius等[1,2,3]于1949年发现, 因此又称为Aurivillius相, 截至上世纪70年代该族被发现的化合物已超过50种[4] ...
1
1950
0.0
0.0
... 铋层状结构由Aurivillius等[1,2,3]于1949年发现, 因此又称为Aurivillius相, 截至上世纪70年代该族被发现的化合物已超过50种[4] ...
1
1950
0.0
0.0
... 铋层状结构由Aurivillius等[1,2,3]于1949年发现, 因此又称为Aurivillius相, 截至上世纪70年代该族被发现的化合物已超过50种[4] ...
2
1971
1.913
0.0
Materials Research Bulletin. 1971, 6(10):null-null
Structural basis of ferroelectricity in bismuth titanate family
... 铋层状结构由Aurivillius等[1,2,3]于1949年发现, 因此又称为Aurivillius相, 截至上世纪70年代该族被发现的化合物已超过50种[4] ...
... 在居里点以下, 绝大多数为正交相, 且当m为奇数时空间群为B2cb, 为偶数时空间群为A21am[4] ...
1
2007
4.593
0.0
Inorganic Chemistry. 2007, 46(10):3839–3850-null
Structure and Bonding in SnWO4, PbWO4, and BiVO4: Lone Pairs vs Inert Pairs
Matthew W. Stoltzfus , Patrick M. Woodward ,* Ram Seshadri , † Jae-Hyun Klepeis , ‡ and Bruce Bursten §
Three ternary oxides, SnWO4, PbWO4, and BiVO4, containing p-block cations with ns2np0 electron configurations, so-called lone pair cations, have been studied theoretically using density functional theory and UV−visible diffuse reflectance spectroscopy. The computations reveal significant differences in the underlying electronic structures that are responsible for the varied crystal chemistry of the lone pair cations. The filled 5s orbitals of the Sn2+ ion interact strongly with the 2p orbitals of oxygen, which leads to a significant destabilization of symmetric structures (scheelite and zircon) favored by electrostatic forces. The destabilizing effect of this interaction can be significantly reduced by lowering the symmetry of the Sn2+ site to enable the antibonding Sn 5s−O 2p states to mix with the unfilled Sn 5p orbitals. This interaction produces a localized, nonbonding state at the top of the valence band that corresponds closely with the classical notion of a stereoactive electron lone pair. In compounds containing Pb2+ and Bi3+ the relativistic contraction of the 6s orbital reduces its interaction with oxygen, effectively diminishing its role in shaping the crystal chemical preferences of these ions. In PbWO4 this leads to a stabilization of the symmetric scheelite structure. In the case of BiVO4 the energy of the Bi 6s orbital is further stabilized. Despite this stabilization, the driving force for a stereoactive lone pair distortion appears to be enhanced. The energies of structures exhibiting distorted Bi3+ environments are competitive with structures that possess symmetric Bi3+ environments. Nevertheless, the “lone pair” that results associated with a distorted Bi3+ environment in BiVO4 is more diffuse than the Sn2+ lone pair in β-SnWO4. Furthermore, the distortion has a much smaller impact on the electronic structure near the Fermi level.
... 从结构上看, 铋层状材料的价带由Bi6s和O2p轨道杂化而成, 这种强的相互作用降低了结构的对称性, 并以偶极子的形式表现出来, 从而引起了一些与偶极子密切相关的性能, 包括铁电、压电和非线性光学性能等[5], 也使其作为光催化材料时具有较高的氧化活性和电荷流动性[6,7] ...
1
2004
1.594
0.0
... 从结构上看, 铋层状材料的价带由Bi6s和O2p轨道杂化而成, 这种强的相互作用降低了结构的对称性, 并以偶极子的形式表现出来, 从而引起了一些与偶极子密切相关的性能, 包括铁电、压电和非线性光学性能等[5], 也使其作为光催化材料时具有较高的氧化活性和电荷流动性[6,7] ...
1
2012
0.531
1.106
Journal of Inorganic Materials. 2012, 27(1):11-18 DOI:10.3724/SP.J.1077.2012.00011
Recent progress on the bismuth containing complex oxide photocatalysts
(Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China)
Photocatalysts scould utilize solar energy to remedy environmental pollutions thus attract world wide attention. Some bismuth-containing complex oxides could be activated by visible light and mineralize organic pollutants. In this paper we reviewed recent progresses on the development of Bi2WO6, BiVO4 and Bi2MoO6 photocatalysts. By controlling the particle size, morphology, crystallinity and other microstructures via different methods, the photocatalytic activities in the degradation of organic dyes, colorless model pollutants such as phenol and acetaldehyde, and disinfection of these visible light induced photocatalysts were greatly enhanced. Through further development, bismuth- containing complex oxides are hopeful to be applied in the field of environmental remediation.
光催化材料因可以利用太阳能净化环境, 受到广泛关注. 一些含铋复合氧化物半导体可直接被可见光激发, 更有效地利用太阳能, 实现有机污染物的矿化, 成为近期光催化材料研究领域的热点之一. 本文概述了Bi2WO6、BiVO4和Bi2MoO6三种常见的含铋复合氧化物可见光催化材料体系的近期研究进展. 通过合成方法的优选、晶粒成核和生长的调节, 实现晶粒尺寸、形貌、结晶度等微结构的控制, 从而获得小尺寸、高表面积的光催化材料, 无论是在有机染料、苯酚和乙醛等多种模拟污染物的矿化, 还是抗菌等方面, 它们皆呈现出优秀的可见光催化性能. 通过进一步发展, 含铋复合氧化物有望实现在环境净化领域的应用.
... 从结构上看, 铋层状材料的价带由Bi6s和O2p轨道杂化而成, 这种强的相互作用降低了结构的对称性, 并以偶极子的形式表现出来, 从而引起了一些与偶极子密切相关的性能, 包括铁电、压电和非线性光学性能等[5], 也使其作为光催化材料时具有较高的氧化活性和电荷流动性[6,7] ...
1
1996
8.238
0.0
Chemistry of Materials. 1996, 8(3):642–649-null
Recent Developments in Oxide Ion Conductors: Aurivillius Phases
Kurt R. Kendall , Carlos Navas , Julie K. Thomas , and Hans-Conrad zur Loye *
Recent advances in the study of Aurivillius phases (Bi2An-1BnO3n+3, n = 1−5) as oxide ion conductors are presented. The structures of modified Aurivillius phases containing extrinsic oxygen vacancies as well as Aurivillius phases containing intrinsic oxygen vacancies are surveyed. A detailed discussion of the conductivity behavior of these Aurivillius phases is given.
... 同时, 铋层状材料结构中本征及非本征氧空位的存在又促使其具有优异的氧离子导电性[8], 这是固态离子导电领域的一大研究对象 ...
1
2011
2.107
0.0
Journal of the American Ceramic Society. 2011, 94(10):3153-3170
Piezoelectric Materials for High Temperature Sensors
Shujun Zhang * andFapeng Yu
Materials Research Institute, Pennsylvania State University, University Park, PA
*Author to whom correspondence should be addressed. e-mails: soz1@psu.edu or shujunzhang@gmail.com
>Piezoelectric materials that can function at high temperatures without failure are desired for structural health monitoring and/or nondestructive evaluation of the next generation turbines, more efficient jet engines, steam, and nuclear/electrical power plants. The operational temperature range of smart transducers is limited by the sensing capability of the piezoelectric material at elevated temperatures, increased conductivity and mechanical attenuation, variation of the piezoelectric properties with temperature. This article discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available and those that are under development. Compared to ferroelectric polycrystalline materials, piezoelectric single crystals avoid domain-related aging behavior, while possessing high electrical resistivities and low losses, with excellent thermal property stability. Of particular interest is oxyborate [ReCa4O (BO3)3] single crystals for ultrahigh temperature applications (>1000°C). These crystals offer piezoelectric coefficients deff, and electromechanical coupling factors keff, on the order of 3–16 pC/N and 6%–31%, respectively, significantly higher than those values of α-quartz piezocrystals (~2 pC/N and 8%). Furthermore, the absence of phase transitions prior to their melting points ~1500°C, together with ultrahigh electrical resistivities (>106 Ω·cm at 1000°C) and thermal stability of piezoelectric properties (< 20% variations in the range of room temperature ~1000°C), allow potential operation at extreme temperature and harsh environments.
... 如表1所示, 相比包括钙钛矿结构在内的其它体系, BLSF在各类压电传感器应用中表现出明显的综合优势, 这种高居里温度、低介电常数、低老化率、高击穿场强、高机械品质因数和优异的谐振频率稳定性使其在高温、高频以及信息存储领域有着重要的应用前景[9,10,11] ...
1
1998
1.143
0.0
Journal of Electroceramics. 1998, 2(4):257-272
Piezoelectric Sensors and Sensor Materials
James F. Tressler (1) , Sedat Alkoy (1) , Robert E. Newnham (1)
1.Materials Research Laboratory, The Pennsylvania State University, University Park, PA, 16802
This paper reviews the current trends and historical development of piezoelectric sensors and sensor materials technology. It begins with a discussion of the bases of piezo- and ferroelectric activity, followed by an overview of the most commonly used piezoelectric ceramic: lead zirconate titanate (PZT). A discussion of the properties and applications of piezoelectric crystals and additional piezoelectric ceramics is followed by a description of several sensor configurations prepared from bulk ceramics. An extensive review and comparison of piezoelectric ceramic—polymer composite sensors based on the connectivity of the constituent phases is also presented. We conclude our discussion of sensor configurations with recent examples of piezoelectric ceramic—metal composite sensors, and expected future developments in the area of piezoelectric sensors.
... 如表1所示, 相比包括钙钛矿结构在内的其它体系, BLSF在各类压电传感器应用中表现出明显的综合优势, 这种高居里温度、低介电常数、低老化率、高击穿场强、高机械品质因数和优异的谐振频率稳定性使其在高温、高频以及信息存储领域有着重要的应用前景[9,10,11] ...
1
2000
0.531
1.106
Journal of Inorganic Materials. 2000, 15(2):209-220
Structures and properties of bismuth layer-structured piezoelectric ceramics with high TC
Shanghai Institute of Ceramics; Chinese Academy of Sciences; Shanghai 200050; China
This paper reviewed the structures and properties of bismuth layer-structured piezoelectric ceramics. The structures of bismuth layer-structured piezoelectric ceramics are built up by the regular intergrowth of (Bi2O2)2+ layers and perovskite (Am-1BmO3m+1)2- slabs where A is a combination of cations adequate for 12-coordinated interstices, B is a combination of cations well suited to octahedral coordinated, and m is an integer usually lying to the range 1-5. By comparison with barium titanate (BaTiO_3) or lead zirconate titanate (PZT) ceramics, the bismuth layer-structured piezoelectric ceramics are characterized by: (1) lower dielectric constant; (2) higher Curie temperature; (3) stronger anisotropy in electromechanical coupling factors; (4) lower ageing rate; (5) higher resistivity; …etc.. Previous studies showed that Curie temperature depends on atomic displacement of polarization cations, spontaneous polarization, bismuth content in the cubooctahedral cavities, and the nature of the substituting cations such as inonic radius, electronegativities and electronic configuration. An essentially weak point of bismuth layer-structured piezoelectric ceramics is low piezoelectric activity which can be solved by chemical substitution or fabrication methods for orientating the grains in ceramics. It is necessary to study the relationships between structures and properties of bismuth layer-structured piezoelectric ceramics in order to develop the materials.
综述了铋层状压电陶瓷的结构特点及性能研究．铋层状压电陶瓷的结构由（Ｂｉ２Ｏ２）２＋层和钙钛矿层（Ａｍ－１ＢｍＯ３ｍ＋１）２－按一定规则共生排列而成．此处 Ａ为适合干 １２配位的离子；Ｂ为适合于八面体配位的离子，ｍ为一整数，其值一般为１～５．与钛酸钡（ＢａＴｉＯ３）或锆钛酸铅（ＰＺＴ）陶瓷相比，铋层状压电陶瓷具有以下特点：低介电常数、高Ｔｃ、机电耦合系数各向异性明显、低老化率、高电阻率等． 先前研究证明，居里温度不仅与极化原子位移、自发极化强度、Ａ位Ｂｉ含量有关，而且还与取代离子的特性诸如离子半径、电负性、核外电子排布有关．压电活性低是铋层状陶瓷的本质缺点，通常发展该材料的途径为化学取代或晶粒取向技术．研究材料结构与性能之间的关系有助于发展铋层状压电陶瓷材料．
... 如表1所示, 相比包括钙钛矿结构在内的其它体系, BLSF在各类压电传感器应用中表现出明显的综合优势, 这种高居里温度、低介电常数、低老化率、高击穿场强、高机械品质因数和优异的谐振频率稳定性使其在高温、高频以及信息存储领域有着重要的应用前景[9,10,11] ...
2
2006
0.376
0.0
Inorganic Materials. 2006, 42(2):189-195 DOI:10.1134/S0020168506020142
Properties of aurivillius phases in the Bi4Ti3O12-BiFeO3 system
1.Russian Academy of Sciences Grebenschikov Institute of Silicate Chemistry ul. Odoevskogo 24/2 St. Petersburg 199155 Russia ul. Odoevskogo 24/2 St. Petersburg 199155 Russia
A number of new Bi m+1Fe m−3TiO3m+3 compounds with integer and fractional m values are identified in the Bi4Ti3O12-BiFeO3 system. All of the compounds are shown to have Aurivillius-type structures. The phase-transition and decomposition temperatures of the new and earlier known compounds of the Bi4Ti3O12-BiFeO3 system are determined. The linear thermal expansion coefficients of the synthesized compounds are evaluated using dilatometry, and their sintering onset temperatures are determined.
... 除一些不常用的表达外, m通常为一整数, 代表了类钙钛矿层中氧八面体的层数, 据推测m不大于12~13, 当m大于8时, 已很难获得BLSF纯相[12] ...
... 随着m值的增大, 铋层状结构特别是其共生结构的超晶格有望逐渐表现出纳米异质结的某些特点[12], 这在一定程度上促使了一些新结构的诞生, 但受结构稳定性的影响, 相关的设计并不十分顺利 ...
2
2002
8.238
0.0
Chemistry of Materials. 2002, 14(4):1455–1471-null
Perovskites by Design: A Toolbox of Solid-State Reactions
Raymond E. Schaak and Thomas E. Mallouk *
In recent years, many soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions. Simple ion-exchange and intercalation reactions replace or modify the interlayer cations of layered perovskites, and more complex metathesis reactions replace interlayer cations with cationic structural units. Topochemical condensation reactions that involve dehydration and reduction provide access to a variety of metastable structural features in three-dimensional perovskites, and similar reactions can be used to convert among higher order layered perovskite homologues. Other techniques, such as high pressure and anion intercalation/deintercalation, also yield interesting metastable phases. When combined, the individual reactions complement each other, and a powerful toolbox of solid-state reactions emerges. By using layered perovskites as templates, it is possible to retrosynthetically design new product perovskites that retain the structural features of the precursor layered phases. The toolbox of reactions was used to synthesize a new Ruddlesden−Popper phase, Na2Sr2Nb2MnO10, and to demonstrate the first example of a complete cycle of reactions of layered perovskites. In addition, topochemical dehydration and reduction were combined to synthesize the new A-site defective cubic perovskite Ca0.67Eu1.33La0.67Ti3O9. It should be possible to extend the toolbox to include more complex systems using layer-by-layer assembly of perovskite thin films, which provide access to “made to order” stacking sequences.
... 就结构而言, BLSF本身属于一类共生结构[13], 是众多共生结构中的一个经典体系, 但通常在BLSF家族中共生结构则专指一类特殊的超晶格结构, 如图1, 这种结构基本都以m值相邻的BLSF单层为基元沿c轴方向交替排列而成, 按照晶体结构中出现的钙钛矿层数, 这种化合物可以表示为m+n结构, 也有少数学者表示为(m+n)/2结构 ...
... 一类典型的钙钛矿衍生结构如图2所示[13], 通常BLSF和Dion-Jacobson相(DJ phase)、Ruddlesden-Popper相(RP phase)同属于钙钛矿结构的层状衍生结构, 它们之间有着类似的特征, 都可以看成在钙钛矿结构中沿c方向周期性的插入了某种结构, DJ相插入了一层碱金属或碱土金属阳离子, RP相插入了两层碱金属阳离子, 而BLSF则插入了一层(Bi2O2)2+层 ...
1
1972
1.913
0.0
Materials Research Bulletin. 1972, 7(10):null-null
Bismuth titanate solid solutions
... Armstrong等[14]收集了大量钙钛矿结构的晶格参数并总结出计算理想钙钛矿MRO3点阵常数ap的经验公式: ...
1
1996
0.0
0.0
... 10时, 钙钛矿结构都很稳定[15] ...
1
1962
2.107
0.0
Journal of the American Ceramic Society. 1962, 45(4):166-169
Crystal Chemistry of Mixed Bismuth Oxides with Layer-Type Structure
E. C. SUBBARAO
Research laboratories, Westinghouse Electric Corporation, Pittsburgh, Pennsylvania
>Several compounds with m= 2, 3, 4, and 5 in the general formula (Me2′O2)2+ (Mem–1 RmO3m+1)2– were synthesized, a number of them for the first time. They possess a layer-type crystal structure. Bi3+ may be the only suitable ion for the Me′ sites; R may be Gas+, Ti4+, Nb5+, or Ta5+. The restrictions on the size of Me ions increases with increasing value of m. Lattice parameter data for the compounds and indexed X-ray powder patterns for m= 5 compounds are presented.
... Subbarao[16]研究发现, 当m=2、4和5时, t值范围分别为0 ...
1
1973
1.527
0.0
Journal of Physics and Chemistry of Solids. 1973, 34(12):null-null
Ordering of crystallographic shear planes-theory of regular arrays
... 弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功 ...
1
1977
0.0
0.0
... 弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功 ...
1
1978
1.534
0.0
Solid State Communications. 1978, 25(8):null-null
On infinitely adaptive crystal structures.
... 弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功 ...
3
1979
1.913
0.0
Materials Research Bulletin. 1979, 14(12):null-null
Stability of layered bismuth compounds in relation to the structural mismatch
... 弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功 ...
... 基于弹性模式, Kikuchi等[20]给出了BLSF中在a-b面内失配应变能的计算公式: ...
... Kikuchi等[20]曾试图在Pb系和Na系中分别合成m& ...
1
1980
2.04
0.0
J. Solid State Chem.. 1980, 32(2):null-null
The elastic strain-energy of crystallog-raphic shear planes in reduced tungsten trioxide
... 弹性模型是处理外延生长中晶格失配常用的一种方法, 最早由Stoneham、Ramasesha、Kittel、Kikuchi、Iguchi等[17,18,19,20,21]将其引入到一系列共生结构的研究中, 用于讨论共生结构的形成机理并获得了成功 ...
2
1992
2.39
0.0
J. Alloys. Compd.. 1992, 188(1/2):null-null
The crystal-chemistry and dielectric-prop-erties of the aurivillius family of complex bismuth oxides with perovs-kite-like layered structures
... , 对应纯的钙钛矿结构)都是可能的[22] ...
... 如图5, 以Bi3TiNbO9为例, 其结构畸变中存在平行于(001)和(100)面的原子运动[22]: ...
1
2011
0.417
0.0
Russian Journal of Inorganic Chemistry. 2011, 56(4):616-620 DOI:10.1134/S0036023611040188
Phase states in the Bi4Ti3O12-BiFeO3 section in the Bi2O3-TiO2-Fe2O3 system
1.Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia
2.St. Petersburg State Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 190013 Russia
Specific features of the thermal behavior of Bi m + 1Fe m−3Ti3O3m + 3 layered perovskite-like compounds (where m takes integer and some fractional values between 3 and 9) were considered, and the temperature limits of stability of these compounds were determined. The phase diagram of the Bi4Ti3O12-BiFeO3 section through the Bi2O3-TiO2-Fe2O3 system was constructed.
... 而其它一些体系, 如Bi4Ti3O12-BiFeO3[23,24]虽然能制备出m值达9的结构, 但当m>5时已很难获得纯相, 而且其热稳定性相对m#cod#x02264 ...
1
2002
0.376
0.0
Inorganic Materials. 2002, 38(7):723-729 DOI:10.1023/A:1016252727831
Synthesis of Am-1Bi2MmO3m+3 compounds in the Bi4Ti3O12-BiFeO3 system
1.Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences
New ferroelectric compounds with a layered perovskite-like structure are obtained in the Bi4Ti3O12–BiFeO3 system. The mechanism of the formation of Am – 1Bi2MmO3m + 3 compounds by solid-state reactions is discussed.
... 而其它一些体系, 如Bi4Ti3O12-BiFeO3[23,24]虽然能制备出m值达9的结构, 但当m>5时已很难获得纯相, 而且其热稳定性相对m#cod#x02264 ...
1
2002
2.04
0.0
J. Solid State Chem.. 2002, 163(2):null-null
Microstructures of some Bi-W-Nb-O phases
... 另外, 如图3(a), Zhou等[25, 29]在一系列Bi-W-Nb-O结构中观察到规律分布的台阶缺陷(step-like defects), 并指出这种缺陷的形成是由于类钙钛矿层中B位原子Nb5+/W6+取代破坏了局部电荷平衡进而引起的结构变化 ...
1
2002
2.21
0.0
... 事实上, 正如Ding等[26]在SrBi2Ta2O9(m=2)中观察到的(图3(b)), 一定程度上也可将超位错看成是没有贯穿的层错, 由于层错的m值与基体的m值不相等, 于是在晶粒内导致一连串的位错或台阶(图3(c)) ...
2
1977
0.0
0.0
... Hutchison等[27,28]在Ba2Bi4Ti5O18(m=5)中频繁地观察到所谓超位错(super-dislocation)的存在, 这种超位错由局部多插入一层氧八面体引起, 会在晶粒内导致连锁错位, 表现为大量台阶缺陷, Hutchison认为这些现象的产生同(Bi2O2)2+层与类钙钛矿层之间晶格失配有关 ...
... Hutchison等[27]在m=8的Bi9Ti3Fe5O27结构中就观察到了m=4和m=5的层错, 而m=5的Ba2Bi4Ti5O18中观察到大量的台阶必然也和层错的存在有关 ...
1
1981
0.0
0.0
... Hutchison等[27,28]在Ba2Bi4Ti5O18(m=5)中频繁地观察到所谓超位错(super-dislocation)的存在, 这种超位错由局部多插入一层氧八面体引起, 会在晶粒内导致连锁错位, 表现为大量台阶缺陷, Hutchison认为这些现象的产生同(Bi2O2)2+层与类钙钛矿层之间晶格失配有关 ...
1
1990
14.829
0.0
Advanced Materials. 1990, 2(2):94-97
Aurivillius phases: Non-superconducting materials?
Dr. Wuzong Zhou
Interdisciplinary Research Centre in Superconductivity University of Cambridge Madingley Road, Cambridge CB3 OHE (UK)
... 另外, 如图3(a), Zhou等[25, 29]在一系列Bi-W-Nb-O结构中观察到规律分布的台阶缺陷(step-like defects), 并指出这种缺陷的形成是由于类钙钛矿层中B位原子Nb5+/W6+取代破坏了局部电荷平衡进而引起的结构变化 ...
2
2004
1.067
0.0
Japanese Journal of Applied Physics. 2004, 43(9S):6653-null
Polarization Properties of Superlattice-Structured Bi4Ti3O12-BaBi4Ti4O15 Single Crystals and Ceramics: Comparison with Bi4Ti3O12 and BaBi4Ti4O15
Tomo Kobayashi 1 , Yuji Noguchi 1,2 and Masaru Miyayama 1
1Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
2PRESTO, Japan Science and Technology Corporation (JST), 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
Superlattice-structured Bi4Ti3O12-BaBi4Ti4O15 (BiT-BBTi) ceramics and single crystals were prepared, and their crystal structure and polarization properties were compared with those of constituent BiT and BBTi. The Curie temperature (TC) of the BiT-BBTi crystals was 540°C, which was 40°C higher than that of the BiT-BBTi ceramics with the stoichiometric composition. The BiT-BBTi ceramics had a remanent polarization (Pr) of 12 µC/cm2, while the spontaneous polarization (Ps) along the a axis of the BiT-BBTi crystals was 52 µC/cm2, which was larger than those of BiT and BBTi crystals. The large Ps observed for the BiT-BBTi crystals is suggested to originate from the ferroelectric displacements of the Bi of Bi2O2 layers as well as from the Bi substitution for Ba induced by compositional deviation.
... Kobayashi等[30,31]在Bi4Ti3O12- BaBi4Ti4O15 (BiT-BBTi, m=3+4)单晶中观察到局部多插入BiT层形成的层错 ...
... Kobayashi等[30,31]对比研究了BiT、BaBi4Ti4O15 (BaBT)和BiT-BaBT, 发现无论是陶瓷还是单晶, BiT-BaBT的剩余极化都要比BiT和BaBT大, 且单晶BiT-BaBT沿a(b)方向的剩余极化达到了52 #cod#x000b5 ...
2
2005
3.794
0.0
... Kobayashi等[30,31]在Bi4Ti3O12- BaBi4Ti4O15 (BiT-BBTi, m=3+4)单晶中观察到局部多插入BiT层形成的层错 ...
... Kobayashi等[30,31]对比研究了BiT、BaBi4Ti4O15 (BaBT)和BiT-BaBT, 发现无论是陶瓷还是单晶, BiT-BaBT的剩余极化都要比BiT和BaBT大, 且单晶BiT-BaBT沿a(b)方向的剩余极化达到了52 #cod#x000b5 ...
1
2011
2.163
0.0
Journal of Materials Science. 2011, 46(16):5423-5431 DOI:10.1007/s10853-011-5483-y
Structural evolution of the interg-rowth bismuth-layered Bi7Ti4NbO21
AbstractA series of intergrowth bismuth-layered ferroelectric Bi7Ti4NbO21 materials are reactive-sintered at 1050 to 1150 °C from Bi3TiNbO9 and Bi4Ti3O12 parent phases to infer their structural characters and microstructure relations. Various types of stacking faults are revealed in the intergrowth structure with extra Bi3TiNbO9 or Bi4Ti3O12 layer(s) by high-resolution transmission electron microscopy; some faults with even spacing form locally new intergrowths of Bi10Ti5Nb2O30 and Bi11Ti7NbO33. Co-growth of Bi7Ti4NbO21 epitaxially grown onto the remaining Bi4Ti3O12 grains is found in the low temperature sintered samples, while the Bi4Ti3O12 co-growth onto the intergrowth grains is also found in the high temperature samples. Both co-growths are created from intergranular melts during a solution-precipitation process, which is consistent with the anisotropic growth of the intergrowth structure and the presence of a Bi-rich intergranular phase. The populations of different stacking faults are found to decrease with the increase of their thickness and also with the increase of sintering temperature, indicating that they are remnants survived from dissolution to imbed via precipitation into the intergrowth structure, which should be created from the smaller but much abundant one-layered remnants of the parent phases. This leads to a new model of structural reorganization by such one-layered units to form the intergrowth structure in this solution-precipitation process. Such incomplete dissolution is initiated by the preferential melting of interleaved [Bi2O2]2+ sheets to enable the exfoliation of perovskite layers to re-order into the intergrowth structure. This reorganization model re-defines the reactive sintering as an evolution process of Bismuth-layered structures.
... 如图4, Gao等[32]在Bi3TiNbO9-Bi4Ti3O12 (BTN-BiT, m=2+3)陶瓷频繁的观察到各种形式的BTN、BiT型层错, 并发现低温样品中的层错会明显高于高温样品 ...
1
2013
0.531
1.106
Journal of Inorganic Materials. 2013, 28(5):561-565 DOI:10.3724/SP.J.1077.2013.12716
Nb Solution within Bi4Ti3O12 sub-structure in the intergrowth bismuth-layered compound Bi7Ti4NbO21
(1. State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China; 2. The Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China; 3. University of Chinese Academy of Sciences, Beijing 100039, China)
In intergrowth bismuth-layered compound Bi7Ti4NbO21, growth defects, such as disordered intergrowth with extra layers of Bi4Ti3O12 or Bi3NbTiO9 constituent sub-structures, or as the co-growth of Bi7Ti4NbO21 onto Bi4Ti3O12 grains, were frequently observed using high-resolution transmission electron microscope (HRTEM)[1]. In order to further find evidence to support the re-ordering picture that was proposed to explain formation of the intergrowth and associated defects, we employ the low- and medium-resolution high-angle annular-dark-field (HAADF) imaging combined with the quantitative energy dispersive X-ray spectroscope (EDXS) analysis to probe into a heavily defected intergrowth structure. A gradual transformation from the ordered intergrowth of both sub-structures to the dominance of Bi4Ti3O12 sub-structure was observed. A substantial level of Nb solution could be detected in n-layered (n≥2) Bi4Ti3O12 sub-structure by spatially-resolved compositional quantification to differentiate the contribution from the adjacent single Bi3NbTiO9 layer. The presence of a finite Nb concentration in the Bi4Ti3O12 sub-structure indicates a substantial and uniform cations inter-change occurred between the two sub-structures, which is inherited most likely from the parent phases via the partially dissolved sintering melts[1].
采用常规高分辨透射电镜(HRTEM)在层状共生化合物Bi7Ti4NbO21中可经常观察到大量生长缺陷:比如插入额外的Bi3TiNbO9或Bi4Ti3O12层而产生的无序共生结构, 以及由共生相Bi7Ti4NbO21和母相Bi4Ti3O12在同一晶粒内形成的共相体[1]。为了给先前提出的共生结构重组生长模型提供更充分的依据, 采用低/中分辨率下的高角环暗场像(HAADF)配合X射线能谱(EDXS)定量分析来研究共生缺陷的产生原因。观察到一种共生缺陷可以从共生相到Bi4Ti3O12母相发生结构渐变。用空间分辨的能谱测量可以排除相邻Bi3TiNbO9层所带来的干扰, 其结果表明Bi4Ti3O12层中固溶了相当含量的Nb。一定量Nb的固溶进一步表明, 在形成共生结构的过程中两种亚结构层之间发生了普遍的阳离子互换过程, 而这一过程应该通过重组模型中的部分溶解液相来实现[1]。
... 同时, 他们研究还发现BiT型层错中存在Nd的固溶, 暗示了层错与成分的密切关系[33] ...
2
1985
0.0
0.0
Bulletin of Materials Science. 1985, 7(3-4):155-178
Intergrowth structures in inorganic solids: A new class of materials
C N R Rao (1)
1.Solid State and Structural Chemistry Unit and Materials Research Laboratory, Indian Institute of Science, 560 012, Bangalore, India
An increasing number of inorganic solids forming long-period structures due to recurrent intergrowth of two chemically distinct but structurally related units are getting to be known in recent years. These novel structures have given rise to new chemistry at solid-solid interfaces. Besides intergrowth structures with long-range order, many solids with random intergrowth (similar to stacking faults in polytypes) are known. Ordered integrowth gives rise to homologous series of structures in many systems. Barium ferrites, the Aurivillius family of oxides and other perovskite-related oxides, siliconiobates, and tungsten oxide bronzes are some of the systems exhibiting ordered intergrowth structures. Both ordered and disordered intergrowths are fruitfully investigated by high resolution electron microscopy. The main emphasis in this article is on intergrowth structures where the component units are compositionally different. These systems are obviously most fascinating since compositional change occurs across each interface (intergrowth plane), unlike in polytypic materials where the composition remains constant. Even in ordered intergrowth structures, there is always some disorder. If order in an intergrowth structure does not prevail over large distances, but occurs only over shorter stretches (say, a few repeats of the sequence), it becomes difficult to describe the solid except in terms of the gross composition and where possible, the unit cell dimensions. Structures with occasional intergrowths are found in a variety of materials such asβ-alumina, Magnéli phases, silicates, ferrites and several other oxide systems. In addition to examining the structural features of various intergrowths, the origin of the intergrowth phenomenon is discussed.
... 事实上, 从Rao等[34,35]关于共生结构的综述可以看出, 层错本身是贯穿各共生体系的一个重要现象, 它的存在引出了共生体系中有序-无序的问题 ...
... 同时, 有序-无序一直都是铋层状结构乃至其它共生体系中一个普遍的现象[34,35], 但却未得到很好的解释, 对这个问题的研究既有利于加深对结构或物相的认识, 也有利于新结构的设计 ...
2
1985
20.833
0.0
Accounts of Chemical Research. 1985, 18(4):113–119-null
Intergrowth structures: the chemistry of solid-solid interfaces
C. N. R. Rao , John M. Thomas
... 事实上, 从Rao等[34,35]关于共生结构的综述可以看出, 层错本身是贯穿各共生体系的一个重要现象, 它的存在引出了共生体系中有序-无序的问题 ...
... 同时, 有序-无序一直都是铋层状结构乃至其它共生体系中一个普遍的现象[34,35], 但却未得到很好的解释, 对这个问题的研究既有利于加深对结构或物相的认识, 也有利于新结构的设计 ...
1
1971
0.415
0.0
... Bi4Ti3O12作为一个特例, 在低温下为单斜相, 对应空间群为m[36,37] ...
1
1990
0.0
0.0
... Bi4Ti3O12作为一个特例, 在低温下为单斜相, 对应空间群为m[36,37] ...
1
2009
41.298
0.0
Chemical Reviews. 2009, 109(12):6858–6919-null
Recent Developments in the Methods and Applications of the Bond Valence Model
Ian David Brown *
... 就价键理论中离子特性而言[38], 在孤对电子的影响下, Bi3+离子与O2-离子成键时会表现出明显的各向异性, 从而造成结构的畸变 ...
2
1999
0.0
0.0
... 而各离子对极化的作用, 可以通过结构中每个离子相对顺电相的偏移量来计算, 公式如下[39,40]: ...
... A位掺杂在BLSF改性的报道近年来层出不穷, 镧系元素是最常用的掺杂取代离子[39, 44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60] ...
2
2000
0.0
0.0
Physical Review B. 2000, 61(10):chrome=1" http-equiv="X-UA-Compatible"/>