微波法制备纳米钛酸钡粉体及其表征

为了探寻价廉、高效合成纳米钛酸钡粉体的方法,以TiCl4和BaCl2为主要原料,采用微波法一步合成纳米钛酸钡粉体,采用X射线衍射谱、扫描电镜、漫反射吸收谱、介电损耗谱和热重-差热分析对钛酸钡粉体进行表征。结果表明,合成的钛酸钡粉体为纯的立方相纳米粉体,颗粒大小均匀,分散性好,晶粒度约为90 nm;纳米钛酸钡粉体的禁带宽度为3.4 eV,具有良好的介电性能;纳米钛酸钡粉体中立方相BaTiO3在1 000℃煅烧后才有部分转化成四方相BaTiO3,表现出良好的热稳定性。     

微波法合成纳米BaTi03及其表征

以TiCl4和BaCl2为主要原料,用微波法一步成功合成纳米BaTiO3,采用X射线衍射谱（XRD）、扫描电镜（SEM）、漫反射吸收谱（DRS）、介电常数谱和热重一差热分析（TG-DTA）表征,XRD和SEM分析表明,合成的BaTiO3为纯的立方相纳米BaTiO3,颗粒大小均匀,分散性好,晶粒粒径在90nm左右;DRS和介电常数测试表明,纳米BaTiO3禁带宽度为3．4eV,具有良好的介电性能;TG-DTA和XRD测试表明,在400℃以前,纳米BaTiO3表面吸附的残余有机物质燃烧放热,有l-4％左右的热失重,对应在290℃左右有较强的放热峰;1000℃煅烧后才有部分立方相的BaTiO3转化成了四方相的BaTiO3,纳米BaTi03表现出了良好的热稳定性。     

氧化锆粉体的Rietveld方法X射线衍射定量相分析

对以不同温度和时间进行热处理的氧化锆粉体,利用X射线步长衍射数据及Rietveld修正方法进行了相含量的定量分析．结果表明,以500℃热处理2h的氧化锆粉体为立方和四方二相混合物（重量比为48：52）．在700℃热处理2h,立方相已消失,部分四方相也相变成单斜相,四方相与单斜相的重量比为35：65．800℃及900℃分别热处理8h及2h都得到接近纯单斜相的氧化锆粉体,四方相的含量分别为5wt％和1wt％．文中也讨论了热处理温度和时间对氧化锆粉体晶粒大小的影响．     

固相法制备超细ZrW2O8粉体及其负热膨胀特性的研究

以化学合成的ZrO2和WO3为原料,以固相法制备具有负热膨胀特性的超细立方相ZrW2O8粉体.对其前驱体进行差热分析(DSC),以X射线粉末衍射(XRD)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)对产物结构及形貌进行表征.结果表明:通过化学方法合成出单斜相和四方相混合的纳米级ZrO2粉体,纯单斜相的纳米级WO3粉体,以其为原料能够制备出超细立方相ZrW2O8粉体.同时考察不同研磨时间对其粒径的影响.变温X射线粉末衍射分析表明:所得ZrW2O8粉体具有很好的负热膨胀特性,在20～600℃范围内的平均热膨胀系数为-6.82×10-6K-1.     

Zn55.24Al18.86Zr25.9的晶体结构研究

采用平衡合金法制备了Zn_(55.24)Al_(18.86)Zr_(25.9)三元化合物的合金样品,利用XRD、扫描电镜(SEM)对样品进行了表征,并使用Rietveld全谱拟合方法对化合物的晶体结构进行了研究。Rietveld精修的可靠性因子为:R_p=7.15%,R_(wp)=9.56%。该化合物属立方晶系,空间群为p4/mmm,点阵常数a=b=4.070 803,c=4.073 669。精修的结果表明Zr原子占据1a位置,部分Zn原子占据2e位置,另一部分Zn原子和Al原子混合占据1c位置。最后通过理论计算验证了所得结构的合理性。     

弱织构热轧钢板氧化皮的定量相分析

首先对具有弱织构热轧钢板表面的氧化皮进行了X射线衍射（XRD）分析,然后选用Highscoreplus软件通过Rietveld全谱拟合方法对得到的XRD谱进行精修,实现了对氧化皮的定量相分析,最后对精修结果进行了择优取向校正,并研究了择优取向校正对拟合结果的影响。结果表明：经过择优取向校正的Rietveld全谱拟合判据均小于未经过择优取向校正的,而经过择优取向校正后的精修结果比未经过择优取向校正的精修结果更准确;Rietveld全谱拟合的结果均为收敛,拟合的判别因子Rp,Rvp和X均较小。     

溶胶凝胶法制备钛酸锶钡(Ba1-xSrx)TiO3陶瓷及其介电性能的研究

采用硝酸钡、硝酸锶、钛酸丁酯和柠檬酸为原料的配合物溶胶凝胶方法制备了(Ba1-xSrx)TiO3(BST)陶瓷.实验结果表明,BST粉体合成温度及烧结温度分别为700及1250℃,均低于传统工艺的相应温度. Sr含量x≥0.40,(Ba1-xSrx)TiO3陶瓷的相结构为立方钙钛矿相;Sr含量x＜0.40,(Ba1-xSrx)TiO3陶瓷的相结构为四方钙钛矿型. (Ba1-xSrx)TiO3(0.5≤x≤0.70)陶瓷的电容率随温度变化曲线,说明存在由铁电四方相到顺电立方相的相变.且随锶(Sr)的摩尔量x的增加,(Ba1-xSrx)TiO3陶瓷样品的相变温度向低温方向移动,相变温度Tc的移动关系为Tc=394.1-272.6x(K).     

ITO粉的Rietveld全谱图拟合定量相分析

对ITO粉样品用Rietveld全谱图拟合法进行了定量相分析，该样品由立方晶型的In2O3和少量的四方晶系的SnO2所组成。In2O3和SnO2质量百分含量分别为94．23％和5．77％。结果表明，用Rietveld法进行了定量相分析是非常有效和准确的。     

超细高纯四方钛酸钡粉体的合成进展

阐述了超细高纯四方钛酸钡(BaTiO3)粉体的主要制备技术及最新进展,特别介绍了这一领域具创新性的连续有序可控爆发成核共沉淀法制备超细高纯四方钛酸钡(BaTiO3)粉体的方法,该方法与其它方法相比具有成本低、产率高和质量好的特点,所制得的粉体分散性好,晶粒尺寸分布范围窄,且平均尺寸在2～100nm范围内可自主调控,特别是不需经晶型转化工艺可直接制备出四方晶相粉末.并介绍了其市场前景及社会经济效益.     

常压液相法制备纳米钛酸钡粉体

以TiCl4、BaCl2·2H2O和NaOH为主要原料，采用常压液相法制备了BaTiO3纳米晶。研究了物料配比、反应物浓度、反应时间等条件对产物组成、产率和粒径大小的影响。采用XRD、TEM等分析手段对样品物相、形貌进行了分析，结果表明，所得BaTiO3粉体的形貌为球形，属立方晶系，钙钛矿结构。其平均颗粒尺寸约为60nm，颗粒尺寸分布均匀，实验证实，当反应温度为70℃、反应时间2h和NaOH：TiCl4=10：1时，所得样品最佳。     

Rietveld refinement study of nanocrystalline copper doped zirconia

Structural studies of Cu-doped zirconia samples with varying Cu content have been carried out. Copper-zirconia samples containing 2-20 mol% Cu were prepared by the co-precipitation technique using tetramethylammonium hydroxide as the precipitating agent and calcined at 773 K in air. The powder XRD data following Rietveld refinement revealed stabilization of zirconia in both tetragonal and cubic phases for all the samples with some monoclinic impurity phase. A decrease in the unit cell parameters of the cubic and tetragonal phase indicates incorporation of copper in the zirconia lattice of both the phases. An increase in the copper concentration (up to 20 mol%) stabilizes zirconia into the cubic phase at the expense of the tetragonal phase, with a decrease in the crystallite size (6-8 nm). Rietveld refinement of the high temperature XRD data reveals that both cubic and tetragonal phases exist up to 723 K with the cubic phase dominating (80% at 723 K). At temperature higher than 723 K, cubic phase gets transformed into the tetragonal phase, which further transforms into the monoclinic phase at 1173 K. At 1173 K, copper comes out of the cubic zirconia lattice forming a separate copper oxide phase and only the tetragonal and monoclinic polymorphs of zirconia exist.     

ZnO/BaTiO3纳米复合材料的制备及其发光性质

采用溶胶-凝胶技术制备了ZnO/BaTiO3纳复合材料，用X射线衍射仪（XRD）、透射电子显微镜（TEM）测定了不同温度处理后样品的组成、结构、形貌和尺寸。对复合材料室温下的光致发光谱分析发现，复合材料的发光强度比纯的纳米ZnO发光显著增强；纳米ZnO中氧空位引起的510nm发光带的峰位随着热处理温度的不同而分别出现蓝移和红移现象。其中蓝移主要是量子尺寸效应引起的，而红移则可能与致密化的BaTiO3所提供的高介电场有关。     

Structural characterization of nanostructured Fe-8P powder mixture

Nanostructured Fe-8P (wt%) powder mixture was prepared by high energy ball milling in a planetary ball mill (Fritsch P7) under argon atmosphere. The morphology of the particles, the phase identification and the alloying evolution process as a function of milling time are studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57Fe M?ssbauer spectrometry (MS), respectively. Refinement based on Rietveld method of the XRD patterns and the M?ssbauer spectra analysis show that the Fe(x)P (1 < x < 2) and Fe2P phosphide phases are the main product after 3 h of milling (approximately 10%). From the XRD Rietveld refinement, it is observed that the Fe2P phase disappears completely after 12 h of milling, while the Fe3P nanophase appears after 9 h and remains for larger milling duration. The lattice structure distortion is evidenced by the lattice parameter changes of the milled products. A two structure state of the alpha-Fe(P) solid solution: alpha-Fe1 and alpha-Fe2 is confirmed by both the XRD and MS measurements. After milling for 21 h, a mixture of a disordered two phase alpha-Fe(P) solid solution, Fe3P nanophase and a small amount of a paramagnetic FeP phosphide phase (approximately 2%) is obtained.     

Synthesis, characterization, structural refinement and optical absorption behavior of PbWO4 powders

The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO₄) powders obtained by the complex polymerization method heat treated at different temperatures for 2 h in air atmosphere. PbWO₄ powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet–visible (UV–vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO₄ powders are free of secondary phases and crystallizes in a tetragonal structure. The UV–vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders.     

Combustion synthesis of nanocrystalline ZrO2 powder: XRD, Raman spectroscopy and TEM studies

ZrO₂ powder was prepared by the gel combustion technique using citric acid as a fuel and nitrate as an oxidant. Calcination at 600 °C of the dried powder, obtained after sluggish combustion of the citrate–nitrate gel, produced nanocrystalline ZrO₂ powder. The Rietveld refinement of the powder XRD data clearly suggested the presence of predominantly tetragonal phase of zirconia. TEM studies showed the agglomerated powder composed of nearly spherical nanocrystals of about 10 nm. The absence of cubic phase of zirconia was conclusively inferred by Raman spectroscopy.     

A sol-powder coating technique for fabrication of yttria stabilised zirconia

Yttria stabilised zirconia has been prepared using a simple sol-powder coating technique. The polymeric yttria sol, which was prepared using 1,3 propanediol as a network modifier, was homogeneously mixed with nanocrystalline zirconia powder and it showed a dual function: as a binder which promoted densification and a phase modifier which stabilised zirconia in the tetragonal and cubic phases. Thermal analysis and X-ray diffraction revealed that the polymeric yttria sol which decomposed at low temperature into yttrium oxide could change the m → t phase transformation behaviour of the zirconia, possibly due to the small particle size and very high surface area of both yttria and zirconia particles allowing rapid alloying. The sintered samples exhibited three crystalline phases: monoclinic, tetragonal and cubic, in which cubic and tetragonal are the major phases. The weight fractions of the individual phases present in the selected specimens were determined using quantitative Rietveld analysis.     

纳米钛酸钡陶瓷的晶体结构

致密的平均尺寸约为30nm钛酸钡陶瓷由压力辅助烧结得到.在变温Raman光谱的基础上,用Rietveld精修方法成功地确定了纳米钛酸钡陶瓷的晶体结构.在室温下,在30nm钛酸钡陶瓷中观测到四方相和正交相的多相共存.这种现象可以用相变产生的内应力来解释.     

BaTiO3铁电薄膜的光致发光研究

以分析纯的乙酸钡和钛酸正四丁酯为前躯体溶液,冰乙酸为溶剂,乙酰丙酮为稳定剂,采用溶胶-凝胶法在硅基上制备了钛酸钡(BaTiO3)铁电薄膜.研究了BaTiO3铁电薄膜的光致发光性能.结果表明,室温下非晶态的BaTiO3铁电薄膜在蓝光激发下具有很强的光致发光现象.其中,经8h 673K退火处理的非晶BaTiO3铁电薄膜的光致发光性能最佳,当455nm光激发时,非晶薄膜在540～660nm内发出强烈的黄光,峰值波长为580～610nm,峰宽约30nm,发光强度随薄膜的厚度增加而增强.晶态BaTiO3铁电薄膜无任何发光现象.