钛酸钡粉体的水热合成实验报告

钛酸钡粉体的水热合成实验报告以下是一份钛酸钡粉体的水热合成实验报告:实验目的：本实验旨在通过水热合成法制备钛酸钡粉体，并研究反应温度、反应时间、反应体系中钡钛比和钡浓度、钛酸四丁酯水解程度以及乙醇用量等因素对钛酸钡粉体颗粒特征的影响。

实验材料：1. 八水合氢氧化钡 (Ba(OH)2·8H2O)2. 钛酸四丁酯 (Ti(OC4H9)4)3. 二氧化钛 (TiO2,30% 金红石型和 70% 锐钛矿型)4. 氨水5. 乙醇和水6. 氯化钠溶液实验步骤：1. 制备钡钛酸盐溶液：将 Ba(OH)2·8H2O 和 Ti(OC4H9)4 分别溶解于水中，然后用氨水调 pH 值为 8-9，制得钡钛酸盐溶液。

2. 制备模板：将一定量的 TiO2 粉体溶解于水中，然后用氢氧化钠溶液调 pH 值为 8-9，制得模板。

3. 模板上生长钛酸钡晶体：将模板放入钡钛酸盐溶液中，调节温度为 (30±2)°C，反应时间为 24 小时。

4. 分离和纯化钛酸钡晶体：将生长好的钛酸钡晶体从模板上取下，用乙醇清洗，然后过滤，用乙醇浸泡，最后离心分离，得到纯化的钛酸钡晶体。

实验结果：通过控制反应温度、反应时间、反应体系中钡钛比和钡浓度、钛酸四丁酯水解程度以及乙醇用量等因素，可以得到不同形状的钛酸钡粉体。

研究发现，随着反应温度的升高，钛酸钡粉体的颗粒大小逐渐减小，平均粒径从 (423.33±11.68) 纳米下降到 (257.33±10.16) 纳米;反应时间的延长有利于钛酸钡由立方相向四方相的转变，但同时也会导致颗粒大小减小。

在最佳的体积比为VTi(OC4H9)4VH2O1.7,VCH3CN2OHVTi(OC4H9)40.6 的情况下，得到的钛酸钡粉体具有最小的平均粒径 (257.33±10.16) 纳米，并且呈现出四方相。

此外，在反应体系中加入适量的氯化钠溶液可以提高钛酸钡粉体的纯度。

化学化工学院材料化学专业实验报告实验实验名称：压电陶瓷材料钛酸钡的制备年级:2015级材料化学日期：2017/09/27姓名：汪钰博学号：222015316210016同组人:向泽灵一、预习部分钛酸钡（BaTiO3）是经典的铁电、压电陶瓷材料，由于其具有高的介电常数，良好的铁电、压电、耐压及绝缘性能，主要用于制作高电容电容器、多层基片、各种传感器、半导体材料和敏感元件；在电子陶瓷、化学化工、国防军事、航空航天等诸多领域中有着极为广泛的应用。

随着现代科学技术的飞速发展和电子元件的小型化、高度集成化，需要制备与合成符合发展要求的高质量的钛酸钡基陶瓷粉体。

目前钛酸钡的主要制备方法有固相法，即氧化物固相烧结法；液相法，即溶胶－凝胶法、水热法和共沉淀法等。

由于固相法无法对钛酸钡生产过程中粉体微观结构和性能进行物理、化学方法的有效控制，从8O年代开始，液相法逐渐成为各国普遍重视的方法。

水热法制备的粉体，由于特殊的反应条件，具有粒度小、分布均匀，团聚较少的优点，且其原料便宜，易得到符合化学计量比并具有完整晶形的产物；同时粉体无需高温煅烧处理，避免了晶粒长大、缺陷的形成和杂质的引入，具有较高的烧结活性等。

但这些工作或者合成的BaTiO3为亚稳态的立方相结构而非四方相，无法满足电子元件性能的需要；或者水热所需的温度高，时间长，从而导致设备成本过高；又或者水热合成需要使用有机钛为原料，从而导致生产成本过高。

这些原因导致无法实现四方相BaTiO3纳米粉末水热合成的规模化生产。

同时水热法在粉体中存在杂质，也限制了该法的应用，因此，尚未见该法在工业上应用的报道，基本上处于实验室探索的阶段。

溶胶---凝胶法多采用蒸馏或重结晶技术保证原料的纯度，工艺过程中不引入杂质粒子，所得粉体粒径小、纯度高、粒径分布窄。

但其原料价格昂贵、有机溶剂具有毒性以及高温热处理会使粉体快速团聚，并且其反应周期长，工艺条件不易控制，产量小，难以放大和工业化。

收稿日期:2005204204 基金项目:国家自然科学基金资助项目(50372039) 作者简介:董敏(19812),男,山西晋城人,硕士生,主要从事水热合成粉体及功能材料的研究。

文章编号:100422474(2006)0520566203镝掺杂钛酸钡纳米粉体的水热合成董　敏1,苗鸿雁1,蒲永平1,2,谈国强1(1.陕西科技大学材料科学与工程学院,陕西咸阳712081;2.西安交通大学电力设备电气绝缘国家重点实验室,陕西西安710049) 摘　要:以BaCl 2・2H 2O 、TiCl 4为反应物,NaO H 为矿化剂,Dy 2O 3为添加剂,水热合成了镝掺杂钛酸钡纳米粉体。

运用X 2射线衍射(XRD )、扫描电镜分析(SEM )等手段研究了镝的掺杂形式、粉体的粒度、微观形貌,讨论了水热处理温度和时间对产物的影响。

结果表明,在220～280℃下水热反应10～16h ,获得粒径为89nm 的Dy 掺杂Ba TiO 3粉体。

所得粉体晶相单一,纯度高,发育完整,团聚少;微量Dy 掺杂时,发生Ba 位取代,掺杂量较高时,部分Dy 3+占据Ti 4+的位置。

关键词:镝掺杂;钛酸钡;纳米粉体;水热合成中图分类号:TQ174 文献标识码:AH ydrothermal Synthesis of Dysprosium Doped B ariumTitanate N anometer PowdersDONG Min 1,MIAO H ong 2yan 1,PU Yong 2ping 1,2,TAN G uo 2qiang 1(1.School of Material Science &Engineering ,Shaanxi University of Science &Technology ,Xianyang 712081,China ;2.State Key Lab.of Electric Insulation for Power Equipment ,Xi ’an Jiaotong University ,Xi ’an 710049,China ) Abstract :Using BaCl 2・2H 2O 、TiCl 4as the basic raw materials ,NaO H as mineralizer and Dy 2O 3as additive ,dysprosium doped barium titanate nanometer powders were prepared by the hydrothermal method.Doping types of dysprosium ,crystallite and micro 2appearance were analyzed by means of XRD and SEM.And the effects of temper 2ature and time of hydrothermal process on products were also discussed.Dysprosium doped barium titanate nanome 2ter particles with the particle size of 89nm ,which are highly pure ,well 2crystallized ,little reunited ,are prepared at the condition of 220～280℃,10～16h.Ba site is substituted by Dy if a little Dy 2O 3is doped but when the Dy 2O 3contents increases ,some Dy 3+ions would take up the positions of Ti 4+.K ey w ords :dysprosium doped ;barium titanate ;nanometer powders ;hydrothermal synthesis Ba TiO 3材料具有良好的介电性能,是电子陶瓷领域应用最广泛的材料之一。

1 前言钛酸钡是电子陶瓷材料的基础原料, 被称为电子陶瓷业的支柱。

它具有高介电常数、低介电损耗、优良的铁电、压电、耐压和绝缘性能, 被广泛的应用于制造陶瓷敏感元件, 特别是正温度系数热敏电阻(PTC)、多层陶瓷电容器(MLCCS)、热电元件、压电陶瓷、声纳、红外辐射探测元件、晶体陶瓷电容器、电光显示板、记忆材料、聚合物基复合材料以及涂层等。

钛酸钡具有钙钛矿晶体结构, 用于制造电子陶瓷材料的粉体粒径一般要求在100nm以内。

因此BaTiO3粉体粒度、形貌的研究一直是国内外关注的焦点。

钛酸钡粉体制备方法有很多, 如固相法、化学沉淀法、溶胶—凝胶法、水热法、超声波合成法等。

最近几年制备技术得到了快速发展, 本文综述了国内外具有代表性的钛酸钡粉体的合成方法, 并在此基础上提出了研究展望。

2 钛酸钡粉体的制备工艺2.1 固相合成法固相法是钛酸钡粉体的传统制备方法, 典型的工艺是将等量碳酸钡和二氧化钛混合, 在1 500℃温度下反应24h, 反应式为: BaCO3+TiO2→BaTiO3+CO2↑。

该法工艺简单, 设备可靠。

但由于是在高温下完成固相间的扩散传质, 故所得BaTiO3粉体粒径比较大(微米), 必须再次进行球磨。

高温煅烧能耗较大, 化学成分不均匀, 影响烧结陶瓷的性能, 团聚现象严重, 较难得到纯BaTiO3晶相, 粉体纯度低, 原料成本较高。

一般只用于制作技术性能要求较低的产品。

2.2化学沉淀法2.2.1 直接沉淀法在金属盐溶液中加入适当的沉淀剂, 控制适当的条件使沉淀剂与金属离子反应生成陶瓷粉体沉淀物团。

如将Ba(OC3H7)2和Ti(OC5H11)4溶于异丙醇中, 加水分解产物可得沉淀的BaTiO3粉体。

该法工艺简单, 在常压下进行, 不需高温, 反应条件温和, 易控制, 原料成本低, 但容易引入BaCO3、TiO2等杂质, 且粒度分布宽, 需进行后处理。

2.2.2 草酸盐共沉淀法将精制的TiCl4和BaCl2的水溶液混合, 在一定条件下以一定速度滴加到草酸溶液中, 同时加入表面活性剂, 不断搅拌即得到BaTiO3的前驱体草酸氧钛钡沉淀BaTiO(C2O4)4·4H2O(BTO)。

化学化工学院材料化学专业实验报告实验名称：压电陶瓷钛酸钡的制备年级：09级材料化学日期：2011-9-7 姓名：蔡鹏学号：222009316210096 同组人：邹磊一、预习部分电子陶瓷用钛酸钡粉体超细粉体技术是当今高科技材料领域方兴未艾的新兴产业之一。

由于其具有的高科技含量，粉体细化后产生的材料功能的特异性，使之成为新技术革命的基础产业。

钛酸钡粉体是电子陶瓷元器件的重要基础原料，高纯超细钛酸钡粉体主要用于介质陶瓷、敏感陶瓷的制造，其中的多层陶瓷电容器、PTC热敏电阻器件与我们的日常生活密切相关，如PTC热敏电阻在冰箱启动器、彩电消磁器、程控电话机、节能灯、加热器等领域有着广泛的应用；MLC多层陶瓷电容在大规模集成电路方面应用广泛。

主要制备方法1，固相法，即氧化物固相烧结法2，液相法，即溶胶---凝胶法，水热法和共沉淀法等固相法简介：以氢氧化钡和钛酸丁酯为原料，采用固相研磨和低温煅烧技术相结合的方法制得钛酸钡纳米材料粉体。

用XRD、TEM、IR和ICP对粉体进行表征结果表明，所得钛酸钡粉体的粒径约为15—20nm，粒子形状近似为球形，晶体结构为立方相，钛钡物质的量比约为1.0.样品制备：称取４．６７９Ｂａ（ＯＨ）２・８Ｈ２０于研钵中研细后，为６６８～８９２℃时，存在于晶格中的羟基被除去。

加人１ｍｌ无水乙醇，拌匀，使Ｂａ（０Ｈ）２・８ＨｚＯ被乙醇充分湿润，然后加入５．ｏｍｌ钛酸丁酯（使反应物中钡与钛的物质的量之比为１．０１ｔ１．ｏ）．混匀后，研磨３０ｍｉｎ，得白色糊状物，放置２４ｈ，变为白色粉末状体。

研细后，置于马弗炉中在不同温度下煅烧３ｈ（将１马弗炉加热到所需温度后再放入样品），产物冷却后。

用５０ｍｌ０．１ｍｏｌ／Ｌ的ＨＡｃ溶液浸泡１ｈ（洗去反应过程中Ｂａ（ＯＨ）２吸收空气中的Ｃ０２生成的ＢａＣ０３），离心分离。

先用蒸馏水洗涤３次，再用蒸馏水和无水乙醇交替洗涤２次，置于恒温干燥箱中于８０℃干燥６ｈ，得ＢａＴｉＯ。

化学化工学院材料化学专业实验报告实验实验名称：压电陶瓷材料钛酸钡的制备年级:材料化学日期：2013-9-26一、预习部分1、前言电子陶瓷用钛酸钡粉体超细粉体技术是当今高科技材料领域方兴未艾的新兴产业之一。

由于其具有的高科技含量，粉体细化后产生的材料功能的特异性，使之成为新技术革命的基础产业。

钛酸钡粉体是电子陶瓷元器件的重要基础原料，高纯超细钛酸钡粉体主要用于介质陶瓷、敏感陶瓷的制造，其中的多层陶瓷电容器、PTC热敏电阻器件与我们的日常生活密切相关，如PTC热敏电阻在冰箱启动器、彩电消磁器、程控电话机、节能灯、加热器等领域有着广泛的应用；MLC多层陶瓷电容在大规模集成电路方面应用广泛。

钛酸钡(BaTiO3)是最早发现的一种具有ABO3型钙钛矿晶体结构的典型铁电体,它具有高介电常数,低的介质损耗及铁电,压电和正温度系数效应等优异的电学性能,被广泛应用于制备高介陶瓷电容器,多层陶瓷电容器,PTC热敏电阻,动态随机存储器,谐振器,超声探测器,温控传感器等,被誉为"电子陶瓷工业的支柱". 近年来,随着电子工业的发展,对陶瓷元件提出了高精度,高可靠性,小型化的要求. 为了制造高质量的陶瓷元件,关键之一就是要实现粉末原料的超细,高纯和粒径分布均匀. 研究可以制备粒径可控, 粒径分布窄及分散性好的钛酸钡粉体材料的方法且能够大量生产成为了一个研究热点.2 钛酸钡粉体的制备工艺2.1 固相合成法固相法是钛酸钡粉体的传统制备方法，典型的工艺是将等量碳酸钡和二氧化钛混合，在1 500℃温度下反应24h，反应式为：Ba CO3+TiO2→BaTiO3+CO2↑。

该法工艺简单，设备可靠。

但由于是在高温下完成固相间的扩散传质，故所得BaTiO3粉体粒径比较大(微米)，必须再次进行球磨。

高温煅烧能耗较大，化学成分不均匀，影响烧结陶瓷的性能，团聚现象严重，较难得到纯BaTiO3晶相，粉体纯度低，原料成本较高。

汤黎辉,张群飞,马金明,肖长江,栗正新(河南工业大学材料科学与工程学院,郑州450001)BaTiO 3纳米粉体的合成方式及合成粉末的样本表征,采取水热法合成方法,合成得到钛酸钡。

通过X 射线衍射、扫描电子显微镜表征手段以及JADE 、Origin 等软件的分析,得出其物相、晶体结构、颗粒大小以及外观形貌。

经过实验,使用水热法合成方式,能够制备出高品质的钛酸钡纳米粉末。

结果表明:用水热法得到了纯的钛酸钡粉体,粉体的晶粒大小较均匀,晶粒尺寸约为39.51nm,粉体的晶体结构为四方结构,形貌为类球形。

;纳米粉体;水热法;晶体结构;晶粒尺寸由于具有出色的介电性能，钛酸钡（BaTiO 3）已经成功地发展出了各种电子器件，如多层陶瓷电容器、正温度系数热敏电阻、动态随机存储器、声呐传感器、压电换能器以及各种光电子元件，从而在电子领域发挥着重要的作用，并且已经成为电子陶瓷领域的主要原材料[1,2]。

目前制备钛酸钡粉体最常用的方法主要有固相法、共沉淀法、微乳液合成方法、水解溶胶-凝胶法等。

固相法作为一种传统的合成工艺，具有制备产率高，操作简单等优点，但是，这种合成方法在制备过程中存在合成温度高、合成的粉体颗粒粗大、较高的杂质含量以及组分均匀度不高等缺点，一般作为低端产品合成时的首选工艺。

共沉淀法制备钛酸钡粉体难以形成均匀的沉淀物，而且颗粒容易团聚，粒径分布宽，产品质量不稳定[3]。

微乳液合成方法制备产物需要大量助剂、改性剂和有机剂，导致成本较高，而且还易引入杂质且产能有限，所以该合成方法目前还没有被广泛的使用，仅仅处于实验室研究中[4]。

凝胶法虽然可行，但由于技术复杂、时间较久，使得它的水解效果不易掌握。

相比之下，水热法更加经济实惠，可以在较短的时间内完成钛酸钡的生产，同时也能够保证产品的质量，能够满足更严格的质量标准[5]。

水热法合成粉体，能够在低温水溶液中得到分散性好的BaTiO 3超细粉体，合成的粉体晶粒发育比较完整，并且在水热法实验过程中，不需要经历高温的煅烧以及后期的球磨过程，进而可以避免了杂质的引入和球磨对粉体结构的破坏，从而有效地消除了杂质及其他形态问题，故文章实验采用水热法制备BaTiO 3纳米粉体，并对其进行深入研究。

Hydrothermal Synthesis of Barium Titanate:Effect of Titania Precursor and Calcination Temperature on Phase TransitionNatarajan Sasirekha,Baskaran Rajesh,and Yu-Wen Chen*Department of Chemical Engineering,Nanocatalysis Research Center,National Central Uni V ersity,Chung-Li320,Taiwan,Republic of ChinaNanosized barium titanate powders were synthesized by a hydrothermal method.The effect of titania precursorson the phase transition of BaTiO3with respect to Ba/Ti ratio,reaction temperature,reaction time,and calcinationtemperature was investigated.The synthesized materials were characterized by X-ray diffraction,scanningelectron microscopy,and transmission electron microscopy.BaTiO3in pure cubic phase with sphericalmorphology was observed with a lower calcination temperature,Ba/Ti ratio,reaction temperature,and time.Increase in the tetragonal phase was ascertained in treatments at higher reaction temperature with a longerreaction time.The lattice hydroxyl release is believed to be the reason for tetragonality at high reaction andcalcination temperatures.To prepare tetragonal BaTiO3using HClO4-TiO2,the optimum synthesis conditionsviz.,Ba/Ti ratio,reaction temperature,and reaction time,are1.2,160°C,and3h,respectively,at a calcinationtemperature of1150°C.The reaction time and reaction temperature for the cubic-tetragonal phasetransformation of BaTiO3shifted toward shorter reaction time and lower reaction temperature when TiO2was synthesized by hydrolysis using HClO4as the acid catalyst.1.IntroductionBarium titanate(BaTiO3),one of the most well-known ferroelectrics,has played an important part in the modern ceramic industry since the discovery of ferroelectric properties in the tetragonal phase of BaTiO3during the1940s.1It has been broadly used as a dielectric material in multilayer ceramic capacitors(MLCCs),2-4printed circuit boards(PCBs),5,6dy-namic random access memory(DRAM),positive temperature coefficient of resistance thermistors(PTCRs),piezoelectric sensors for ultrasonic and measuring devices,pressure transduc-ers,infrared detectors,and electrooptic devices7-9due to its unique perovskite structure(ABO3)and exceptionally high dielectric[(2-5)×103]10and piezoelectric properties at room temperature.However,these outstanding behaviors mainly depend on the crystal structure,shape,size,stoichiometry, homogeneity,and surface properties of BaTiO3,which in turn depends on the synthesis method.Among the crystal structures of BaTiO3,the cubic phase exhibits paraelectric properties,while the tetragonal phase shows ferroelectric properties.The direct generation of tetragonal BaTiO3is of considerable interest. The conventional synthesis of barium titanate compounds typically involves high-temperature(∼1200°C)calcinations of a BaCO3and TiO2powder mixture,which often results in low purity and polydispersity due to high reaction temperature and heterogeneous solid-phase reaction.11,12Nevertheless,fine Ba-TiO3ceramics can be prepared by wet-chemistry synthesis techniques,including the coprecipitation method,13coprecipi-tation in combination with the inverse microemulsion method,14,15 sol-gel processing,16,17the hydrothermal method,18-21spray pyrolysis,22the oxalate route,23the high-temperature ceramic route,the microwave hydrothermal method,24-27and the polymeric precursor method.28Hydrothermal synthesis for the preparation of crystalline BaTiO3has gained popularity recently.29-33It involves the chemical reactions of Ba(OH)2,TiO2,or gels of Ba-Ti acetate mixtures at a high temperature.It has the advantage of producing finer particles with more uniform size.In addition,the interac-tion between the solid and fluid phases determines the physical characteristics of BaTiO3,and hence,the synthesis allows one to control the particle size by adjusting the synthesis parameters, such as the reaction temperature,time,and pH values.The synergistic effect of solvent,temperature,and pressure on the ionic reaction equilibrium in the hydrothermal reaction medium can stabilize the formation of BaTiO3and retards the formation of impurities.Also,the precursors for the preparation of BaTiO3 by hydrothermal synthesis are readily available,inexpensive, and easy to handle,which makes the hydrothermal synthesis an easy and effective method to adopt for the synthesis of BaTiO3.Although the hydrothermal synthesis has the above-mentioned advantages,the formation and growth mechanisms in BaTiO3synthesis have not been well understood.There are a few articles about the study of phase transformation of BaTiO3 with preparation conditions.However,so far there is no report about the effect of titania precursor,which plays a vital role in the growth mechanism of BaTiO3synthesis,on the phase transformation of BaTiO3.In this paper,a systematic investiga-tion on the effect of titania precursor on phase transformation of BaTiO3with respect to Ba/Ti ratio,reaction temperature, reaction time,and calcination temperature is presented.2.Experimental Section2.1.Hydrothermal Synthesis of BaTiO3.Barium titanate powders were synthesized by hydrothermal method.All the reagents used were of analytical grade.Hydrothermally produced TiO2particles34prepared using hydrochloric acid and perchloric acid as acid precursors were used as the titania source.The detailed characteristics of these materials have been presented in our previous paper.34Ba(OH)2‚8H2O(Showa Chemical Co., Ltd.)and TiO2powder(rutile)34were mixed with a Ba/Ti ratio (1.2,1.4,1.6,1.8,2.0)in a50mL autoclave with45mL of deionized water.The autoclave was sealed,shaken,and placed in an oven at160°C for a variable reaction period ranging from*To whom correspondence should be addressed.Tel.:(886)3422751,ext34203.Fax:(886)34252296.E-mail:ywchen@cc.ncu.edu.tw.1868Ind.Eng.Chem.Res.2008,47,1868-187510.1021/ie070986m CCC:$40.75©2008American Chemical SocietyPublished on Web02/16/20083to 24h.After cooling naturally to room temperature,the contents of the autoclave were diluted in 90mL of 0.1M formic acid with stirring for 5min in an attempt to remove any BaCO 3formed and the addition of excess Ba 2+to the starting solution.The mixture was filtered and washed with distilled water (500mL)three times,and the residue was dried in oven at 100°C for 24h.2.2.Characterization.The crystalline phase of BaTiO 3was analyzed by powder X-ray diffraction (XRD)using a Siemens D500automatic powder diffractometer.Nickel-filtered Cu K R radiation (λ)0.15418nm)was used with a generator voltage of 40kV and a current of 29mA.Bragg -Brentano focusing geometry was employed with an automatic divergence slit (irradiated sample length was 12.5nm),a receiving slit of 0.1nm,a fixed slit of 4°,and a proportional counter as a detector.It was operated in the step scan mode,at scanning speeds of 0.1°2θ/s and 1s step time in the range 20-80°for barium titanate.Scherrer’s equation 35was used to calculate the crys-tallite size of barium titanate crystals from the full width at half-maximum of the XRD peak.The morphology of the particles was analyzed by scanning electron microscopy (SEM)and transmission electron micros-copy (TEM).SEM images were acquired with a Hitachi S-800field emission microscope using an acceleration voltage of 20kV.The samples were coated with Au prior to analysis and imaged directly.TEM images were obtained on a JEOL JEM-2000FX Πmicroscope using an electron beam generated by a tungsten filament and an accelerating voltage of 160kV,a beam diameter of approximately 1-2µm,and an objective lens aperture of 20µm.The sample grids were prepared via sonication of powdered sample in ethanol for 10min and evaporating 1drop of the suspension onto a carbon-coated,porous film supported on a 3mm,200-300mesh copper grid.TEM images were recorded at a magnification of 100000-400000×.The magnification was calibrated in pixels per nanometer on the camera.3.Results and Discussion3.1.Effect of Ba/Ti Ratio.BaTiO 3powder,prepared with Ba/Ti ratio in the range of 1.2-2.0,was characterized by XRD,SEM,and TEM techniques to study the cubic -tetragonal phase transformations and surface modifications of BaTiO 3.The ratio of Ba/Ti was chosen to be greater than 1to avoid contamination of BaTiO 3(s)with excess TiO 2(s)under the conditions of hydrothermal synthesis.24Furthermore,Ba/Ti >1increases the pH of the solution,which is an important thermodynamicvariable for the synthesis of perovskite materials,and helps to avoid the addition of an alkaline mineralizer to facilitate the formation of BaTiO 3.According to the thermodynamic calcula-tions of stability diagrams for the hydrothermal Ba -Ti system,high pH and Ba/Ti >1are necessary for the synthesis of high-purity BaTiO 3crystals.28XRD patterns of the as-synthesized BaTiO 3,with Ba/Ti ratios of 1.2,1.4,1.6,1.8,and 2.0,showed the characteristic peaks of both cubic BaTiO 3(JCPDS File No.79-2263)and those of BaCO 3for both TiO 2precursors.Modest BaCO 3contamination was noted in almost all the samples due to the introduction of airborne CO 2,which would dissolve as CO 32-and reacts with Ba 2+to form BaCO 3during the posttreatment.26,36The formation of BaCO 3,observed in this work,is quite common in the hydrothermal processing as BaCO 3can precipitate at lower pH values than those needed to precipitate BaTiO 3.24AccordingtoFigure 1.XRD patterns of BaTiO 3synthesized at various Ba/Ti ratios using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors and washed with formic acid followed by calcination at 900°C (2h).Table 1.Effect of Ba/Ti Ratio and Calcination Temperature on the Crystalline Phase of BaTiO 3calcination temp (°C)Ti precursor Ba/Ti ratio synthesis temp (°C)synthesis time (h)9001150crystalline phase HCl-TiO 21.21606--cubic 1.41606--cubic 1.61606--cubic 1.81606--cubic2.01606--cubic HClO 4-TiO 21.21606--cubic 1.41606--cubic 1.61606--cubic 1.81606--cubic2.01606--cubic HCl-TiO 21.21606yes -cubic 1.41606yes -cubic 1.61606yes -cubic 1.81606yes -cubic2.01606yes -cubic HClO 4-TiO 21.21606yes -cubic 1.41606yes -cubic 1.61606yes -cubic 1.81606yes -cubic2.01606yes -cubic HCl-TiO 21.21606-yes cubic 1.41606-yes cubic 1.61606-yes cubic 1.81606-yes cubic2.01606-yes cubic HClO 4-TiO 21.21606-yes tetragonal 1.41606-yes tetragonal 1.61606-yes tetragonal 1.81606-yes tetragonal2.01606-yestetragonalInd.Eng.Chem.Res.,Vol.47,No.6,20081869the thermodynamic stability diagram of Ba -Ti systems,BaCO 3precipitates at lower pH values than those needed to precipitate BaTiO 3.28Moreover,the formation of BaCO 3is more predomi-nant in BaTiO 3prepared using HClO 4-TiO 2,which indicates its lower pH compared with those prepared using HCl-TiO 2.The relative pH of HClO 4is lower than that of HCl as the p K a values of HClO 4and HCl are -10and -7,respectively.37The XRD results of the as-synthesized BaTiO 3illustrate the absence of apparent peak splitting at 2θ)45°,which corre-sponds to the tetragonal phase of BaTiO 3(JCPDS Card No.5-0626)and hence confirmed the cubic structure with symmetry Pm 3m .In order to remove BaCO 3,the powders were washed with formic acid and calcined at 900°C for 2h.Figure 1shows XRD patterns of BaTiO 3chemically treated with formic acid and calcined at 900°C,which confirms the removal of BaCO 3from BaTiO 3prepared using HCl-TiO 2and HClO 4-TiO 2.Moreover,it indicates that there is no change in the cubic phase of BaTiO 3upon treatment with formic acid.The effect of Ba/Ti ratio and calcination temperature on the crystal structure of BaTiO 3is summarized in Table 1.It can be observed that,even at a Ba/Ti molar ratio of 2without heat treatment,the tetragonal splitting of the diffraction peaks corresponding to the (200)and (002)planes of the perovskite BaTiO 3could not be distinguished,indicating the presence of pure cubic crystalline phase.Shi et al.36observed tetragonal BaTiO 3crystallites when the precursor with high Ba/Ti molar ratio of 3was used,which reduces the probability of forming barium vacancies and stabilized tetragonal phase.The influence of calcination temperature at various Ba/Ti ratios on the cubic -tetragonal phase transition of BaTiO 3can be observed by comparing Figures 1and 2.Figure 2shows the XRD patterns of BaTiO 3prepared using HCl-TiO 2and HClO 4-TiO 2,subjected to calcination at 1150°C.For BaTiO 3samples prepared using HCl-TiO 2,the XRD results show that the crystalline phase is metastable cubic phase for all the samples at 900and 1150°C.The peaks are very sharp,indicating that the crystalline structure is well developed.Generally,the tetragonality of BaTiO 3is deduced from the plane spacing of (002)over that of (200);the corresponding peak appears near 45°in the XRD patterns.Because the peak splitting at 45°is a predominant one to confirm the formation of tetragonal phase,tetragonal splitting of the peaks corresponding to (200)and (002)planes have been chosen to verify the formation of tetragonal phase.Normally,BaTiO 3cubic -tetragonal phase changes begin at 900and 1150°C,but for BaTiO 3prepared using HCl-TiO 2the phase transformation does not proceed to completion even at 1150°C.In the case of BaTiO 3prepared using HClO 4-TiO 2and calcined at 900°C,the XRD patterns are almost identical irrespective of Ba/Ti ratio and cubic phase is observed.However,tetragonal phase was observed at 2θ)45°for the powders synthesized at Ba/Ti ratios of 1.2,1.4,1.6,1.8,and 2.0and calcined at 1150°C for 2h,as shown in Figure 2b.A slight increase in the intensity of tetragonal phase with Ba/Ti ratio may be due to the removal of barium vacancies (charge compensator of OH -defect)by excess barium content,which stabilizes tetragonality.Figures 3and 4show the SEM pictures of BaTiO 3samples prepared using HCl-TiO 2and HClO 4-TiO 2,respectively,at various Ba/Ti ratios of 1.2,1.4,1.6,and 1.8.The particles agglomerated in a spherical shape with ca.0.05-0.15µm (ca.50-150nm)diameters.A possible mechanism for the formation of BaTiO 3by hydrothermal synthesis is the dissolution-Figure 2.XRD patterns of BaTiO 3synthesized at various Ba/Ti ratios using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors and calcined at 1150°C (2h).Figure 3.SEM micrographs of as-synthesized BaTiO 3prepared using HCl-TiO 2at various Ba/Ti ratios:(a)1.2,(b)1.4,(c)1.6,and (d)1.8.1870Ind.Eng.Chem.Res.,Vol.47,No.6,2008precipitation method,38in which there is a chemical equilibrium between TiO 2and [Ti(OH)x ]4-x .[Ti(OH)x ]4-x ,which is a highly active species,can combine with Ba 2+to form a new nucleus,and hence,with an increase in Ba/Ti ratio the chance for the formation of a new nucleus by [Ti(OH)x ]4-x increases and leads to a decrease in the particle size of BaTiO 3.Figure 3shows the decrease in the particle size of BaTiO 3with an increase in Ba/Ti ratio,which is in accord with the dissolution -precipitation mechanism.TEM results show that the primary particles of the sample prepared at Ba/Ti ratios of 1.2and 1.4using HCl-TiO 2as precursor are spherical in shape with 50-60nm diameters,as shown in Figure 5a,b,whereas the particle sizes of BaTiO 3prepared using HClO 4-TiO 2are in the range of 40-50nm diameters (Figure 5c,d).Moreover,it can be ascertained from TEM images that the Ba/Ti ratio increases the cluster size of primary particles.Besides,it should be noted that the stability of cubic and tetragonal phases depends on the critical size of BaTiO 3particles and the critical size was reported to be ∼50nm.39The crystallite size of BaTiO 3is a principal factor controlling tetragonality because the surface defects of nanoc-rystallites are predominant over the bulk ones below a certain critical size of BaTiO 3.The surface defects can prevent the completion of phase transformation,leading to high strains within the crystal.Increase in the cluster size of primary particles reduces the strain within the cubic structure for distortion.It can be concluded that the phase transition of cubic BaTiO 3occurs at 1150°C irrespective of Ba/Ti ratio when HClO 4-TiO 2was used as the TiO 2precursor.Moreover,the primaryparticleFigure 4.SEM micrographs of as-synthesized BaTiO 3prepared using HClO 4-TiO 2at various Ba/Ti ratios:(a)1.2,(b)1.4,(c)1.6,and (d)1.8.Figure 5.TEM micrographs of BaTiO 3prepared using (a)HCl-TiO 2,Ba/Ti )1.2;(b)HCl-TiO 2,Ba/Ti )1.4;(c)HClO 4-TiO 2,Ba/Ti )1.2;and (d)HClO 4-TiO 2,Ba/Ti )1.4.Figure 6.XRD patterns of BaTiO 3synthesized at various temperatures using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors calcined at 900°C (2h).Ind.Eng.Chem.Res.,Vol.47,No.6,20081871size of BaTiO 3prepared using HClO 4-TiO 2is smaller than that prepared using HCl-TiO 2,which can be ascribed to the smaller particle size of TiO 2prepared by HClO 4.34The agglomeration of BaTiO 3nanoparticles at higher calcination temperature promotes the stability of the tetragonal phase.3.2.Effect of Synthesis Temperature.To study the influence of synthesis temperature on the phase of BaTiO 3and particle morphology,BaTiO 3was prepared at 80,120,160,180,and 200°C while keeping the rest of the process parameters as Ba/Ti )1.2and the synthesis time as 6h.The XRD patterns of BaTiO 3obtained at different reaction temperatures and calcined at 900°C are given in Figure 6.The XRD results illustrated well-developed cubic crystalline phase and the intensity of the peaks increased with reaction temperature.There is a possibility of decrease in the unit-cell volume and decrease in density with an increase in the reaction temperature due to the release of lattice hydroxyls.20The influence of calcination temperature withsynthesis temperature is compiled in Table 2.Figure 7depicts the XRD patterns of BaTiO 3calcined at 1150°C.With increased synthesis temperature,the diffraction peaks related to the (200)and (002)planes of the tetragonal BaTiO 3separated and the c /a ratio of the lattice increased,confirming the cubic -tetragonal phase transition with synthesis temperature.The splitting of the (200)reflection is apparent for the samples synthesized at 180and 200°C,suggesting the tetragonal phase.The intensity ratio of 45°peaks significantly increased as the synthesis temperature increased.The presence of shoulders at 80and 120°C represents the formation of partially tetragonal phase in cubic BaTiO 3.The stabilization of tetragonal phase with increase in temperature may be due to the removal of hydroxyl groups in the BaTiO 3lattice.Figure 8depicts the SEM micrographs of BaTiO 3prepared using HCl-TiO 2at 80,120,180,and 200°C for 24h.The particles agglomerated into a spherical shape,and the particle sizes estimated from the SEM micrographs are within 0.05-0.15µm in diameter.When the synthesis temperature increased from 80to 200°C and with reacting for 24h,the particle size of BaTiO 3increased to 0.09-0.15µm.The shape of the particles was observed to be spherical independent of treated tempera-tures.The increase in the synthesis temperature leads to an increase in the particle size,which may explain the stronger agglomeration at higher temperature.However,for BaTiO 3prepared using HClO 4-TiO 2(Figure 9),the secondary particle size increased from 0.05to 0.10µm with an increase in the reaction temperature from 80to 200°C for 24h,confirming that the particle size of BaTiO 3was dependent on synthesis temperature.The overall shape of the agglomerated secondary particle size was estimated to be 0.05-0.10µm in diameter.As shown in Figure 10,the particles consist of near-monodis-perse spherical nanoparticles of BaTiO 3.The agglomeration of primary particles with an increase in the reaction temperature can be identified from TEM images,as shown in Figure 10.The clusters of primary particles observed for HClO 4-TiO 2precursor are more than those of HCl-TiO 2.This result suggested that the crystallite size is one of the vital factors that control tetragonality.At a higher reaction temperature,the phase transition has occurred from cubic to tetragonal.3.3.Effect of Calcination Temperature.The stability of the cubic phase in BaTiO 3prepared by hydrothermal synthesis at room temperature may be accounted for by the presence of weakly bound water molecules absorbed onto the surface of the particles and the more strongly bonded structural water as lattice OH -ions.The content of barium vacancy as well as OH -defects in the cubic crystallites is higher than that inTable 2.Effect of Synthesis Temperature and Calcination Temperature on the Crystalline Phase of BaTiO 3calcination temp (°C)Ti precursor Ba/Ti ratio synthesis temp (°C)synthesis time (h)9001150crystalline phase HCl-TiO 21.2806--cubic 1.21206--cubic 1.21606--cubic 1.21806--cubic 1.22006--cubic HClO 4-TiO 21.2806--cubic 1.21206--cubic 1.21606--cubic 1.21806--cubic 1.22006--cubic HCl-TiO 21.2806yes -cubic 1.21206yes -cubic 1.21606yes -cubic 1.21806yes -cubic 1.22006yes -cubic HClO 4-TiO 21.2806yes -cubic 1.21206yes -cubic 1.21606yes -cubic 1.21806yes -cubic 1.22006yes -cubic HCl-TiO 21.2806-yes cubic 1.21206-yes cubic 1.21606-yes cubic 1.21806-yes tetragonal 1.22006-yes tetragonal HClO 4-TiO 21.2806-yes cubic 1.21206-yes cubic 1.21606-yes tetragonal 1.21806-yes tetragonal 1.22006-yestetragonalFigure 7.XRD patterns of BaTiO 3synthesized (Ba/Ti )1.2)at various temperatures using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors and calcined at 1150°C (2h).1872Ind.Eng.Chem.Res.,Vol.47,No.6,2008tetragonal phase.The cubic -tetragonal phase transformation at higher reaction temperature and calcination temperature is due to the elimination of OH -vacancies from the lattice with heat treatment,which leads to the tetragonal stability.At the Curie point,where BaTiO 3undergoes a phase transition,the relative displacement of cation sublattice to O 2-sublattice causes the phase transition of BaTiO 3from cubic to tetragonal.The oxygen vacancies have significant mobility above 650°C,whereas the cation vacancies acquire measurable mobility only above 1050°C.24Moreover,the decrease in the lattice parameter of the crystallites with temperature led to the conclusion that the removal of OH -defects caused the enlargement of the unit cell and released the lattice strain to form the tetragonal phase.3.4.Effect of Synthesis Time.The effect of synthesis time on the formation of crystalline BaTiO 3was also studied by performing the experiments at different reaction times ranging from 3to 24h at 160°C with Ba/Ti )1.2.The crystalline form at shorter periods of time,viz.,3and 6h,is primarily the metastable cubic form.SEM micrographs indicated no signifi-cant difference in the morphology.The cluster size was larger by extending the processing time,but the particle size has no significant difference.BaTiO 3powders prepared by using HClO 4-TiO 2as the precursor resulted similarly to those prepared by using HCl-TiO 2as the precursor.The XRD patterns as shown in Figure 11confirm the cubic phase of BaTiO 3prepared using HCl-TiO 2and HClO 4-TiO 2calcined at 900°C.Figure 12a shows the typical phase transformation of BaTiO 3prepared using HCl-TiO 2.When BaTiO 3prepared using HCl-TiO 2was treated for 12h,a noticeable peak splitting appeared.With increasing reaction time from 12to 24h,the intensity and sharpness of the tetragonal peak splitting increased,indicating an increase in the crystallinity of the tetragonal phase along with anincreaseFigure 8.SEM micrographs of BaTiO 3synthesized using HCl-TiO 2at various temperatures:(a)80,(b)120,(c)180,and (d)200°C.Figure 9.SEM micrographs of BaTiO 3synthesized using HClO 4-TiO 2at various temperatures:(a)80,(b)120,(c)180,and (d)200°C.Figure 10.TEM micrographs of BaTiO 3prepared using (a)HCl-TiO 2,120°C;(b)HCl-TiO 2,180°C;(c)HClO 4-TiO 2,120°C;and (d)HClO 4-TiO 2,180°C.Ind.Eng.Chem.Res.,Vol.47,No.6,20081873in the particle size of BaTiO 3.The results are summarized in Table 3.The tetragonal BaTiO 3can be synthesized from HCl-TiO 2at reaction times of 12and 24h using Ba/Ti ratio of 1.2,synthesis temperature of 160°C,and calcination temperature at 1150°C for 2h.However,even at 3h reaction time,BaTiO 3prepared using HClO 4-TiO 2achieved the cubic -tetragonal phase transformation (Figure 12b).The reason can be ascribed to the acidic nature of HClO 4,which leads to the formation of BaTiO 3with fewer defects so as to stabilize the tetragonal phase apart from the possible influence of Cl -ions present in the reaction mixture.The presence of chloride ions is speculated to influence the diffusion of Ba 2+ions and retard the crystal growth process,thereby stabilizing the tetragonal phase by forming larger crystals.40In the early stage of reaction,chloride ions produce more nuclei and form smaller particles,which grow larger at prolonged time.Sun and Li 41reported that BaTiO 3particles synthesized in the presence of chloride ions are slightly larger than the particles synthesized in the absence of chloride ions,however,with an enhanced tetragonality compared to the latter.The physicochemical properties of TiO 2prepared from HCl and HClO 4make the difference in the properties of BaTiO 3.34Therefore,it is concluded that the BaTiO 3tetragonal phase can be successfully synthesized using HClO 4-TiO 2as the precursor at a [H +]/[Ti 4+]ratio of 1.2,synthesis temperature of 160°C,and calcination temperature of 1150°C (2h).344.ConclusionIn the present study,the morphology and phase transformation of BaTiO 3prepared using HCl-TiO 2and HClO 4-TiO 2with respect to reaction temperature,reaction time,Ba/Ti ratio,and calcination time were investigated.Increase in Ba/Ti ratio,temperature,and reaction time increases the possibility of cubic phase transformations.Well-crystallized tetragonal BaTiO 3powders of high purity were obtained using HCl-TiO 2as the precursor at optimum conditions of Ba/Ti ratio )1.2,temper-Figure 11.XRD patterns of BaTiO 3synthesized at various reaction times using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors calcined at 900°C (2h).Figure 12.XRD patterns of BaTiO 3synthesized at various reaction times using (a)HCl-TiO 2and (b)HClO 4-TiO 2precursors.Conditions:reaction temperature )160°C;Ba/Ti )1.2;calcination temperature )1150°C (2h).Table 3.Effect of Synthesis Time and Calcination Temperature on the Crystalline Phase of BaTiO 3calcination temp (°C)Ti precursor Ba/Ti ratio synthesis temp (°C)synthesis time (h)9001150crystalline phase HCl-TiO 21.21603--cubic 1.21606--cubic 1.216012--cubic 1.216024--cubic HClO 4-TiO 21.21603--cubic 1.21606--cubic 1.216012--cubic 1.216024--cubic HCl-TiO 21.21603yes -cubic 1.21606yes -cubic 1.216012yes -cubic 1.216024yes -cubic HClO 4-TiO 21.21603yes -cubic 1.21606yes -cubic 1.216012yes -cubic 1.216024yes -cubic HCl-TiO 21.21603-yes cubic 1.21606-yes cubic 1.216012-yes tetragonal 1.216024-yes tetragonal HClO 4-TiO 21.21603-yes tetragonal 1.21606-yes tetragonal 1.216012-yes tetragonal 1.216024-yestetragonal1874Ind.Eng.Chem.Res.,Vol.47,No.6,2008ature)180°C,synthesis time)6h,and calcination at 1150°C for2h.However,the phase transformation of BaTiO3 prepared using HClO4-TiO2occurred at lower reaction temper-ature(160°C)and synthesis time(3h)than BaTiO3particles prepared using HCl-TiO2.BaTiO3particles are agglomerated to a spherical shape with ca.80-90nm and BaTiO3particles synthesized with HClO4-TiO2were smaller than those prepared by HCl-TiO2.The stabilization of cubic BaTiO3is caused by defects including OH-defects and barium vacancies.The formation of tetragonal BaTiO3is promoted by the use of high reaction temperature,calcination temperature,and reaction time, which reduces the probability of forming OH-vacancies.In summary,the precursor has a strong influence on the size and morphology of BaTiO3.BaTiO3prepared from HClO4-TiO2 indeed increases the transformation of cubic-to-tetragonal phase at lower reaction conditions without significant particle growth. 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实验8 钛酸钡粉体的水热合成一、实验目的1. 熟悉水热法的实验操作方法与注意事项。

2. 掌握钛酸钡的性质、应用和水热合成方法。

二、实验原理钛酸钡(BaTiO3)，又称偏钛酸钡，属于钙钛矿(ABO3)结构。

钛酸钡具有良好铁电、压电性能、高的介电常数、耐压及绝缘性能，广泛应用于小体积、容量大的微型电容器、电子计算机记忆元件、压电陶瓷等，它是电子工业和特种陶瓷领域应用最为广泛的材料之一，也是附加值较高的无机精细化工产品。

现常用的合成方法是液相法(湿化学法)，包括溶胶-凝胶法、水热法、化学沉淀法等，本实验主要采用水热法合成钛酸钡粉体。

水热合成是无机合成的一个重要分支。

水热合成研究从模拟自然界矿石生成到沸石分子筛和其他晶体的合成，已经经历了100多年的历史。

它是指在高压釜中，通过对反应体系加热加压(或自生蒸气压)，创造一个相对高温、高压的反应环境，进行无机合成与材料处理的一种有效方法。

水热法已成为目前多数无机功能材料、特种组成与结构的无机化合物以及特种凝聚态材料，如超微粒、溶胶与凝胶、非晶态、无机膜等合成的越来越重要的途径。

水热合成有以下特点：(1)能够使低熔点化合物、高蒸气压且不能在熔体中生成的物质、高温分解相在水热与溶剂热低温条件下晶化生成。

(2)水热合成的低温、等压、溶液条件，有利于生成极少缺陷、取向好、完美的晶体且合成产物结晶度高，易于控制晶体的粒度。

(3)由于易于调节水热条件下的环境气氛，因而有利于中间价态与特殊价态化合物的生成，并能均匀地进行掺杂。

(4)由于在水热条件下中间态、介稳态以及特殊物相易于生成，因此能合成开发一系列特种介稳结构、特种凝聚态的新合成产物。

本实验采用水热合成法，将原料钡盐和钛盐按比例配制成前驱体，并在前驱体中加入适量的强碱作为矿化剂来调节反应溶液的酸碱度，将配制好的前驱体装入水热反应釜中，控制合适的反应温度、压力以及反应时间，进行水热反应，从而合成所需的多晶钛酸钡(BT)粉体。