半结晶聚酯的两相分离及其可靠性分析

联用Rietveld方法、Fourier过滤技术和径向分布函数(RDF)研究了半结晶聚酯(PET)粉末样的结晶相和非晶相两相分离及结构分析问题，得到合理的结晶相和非晶相的结构参数，表明这种方法对分析半结晶高聚物的两相结构是可行的.文中提出，判断半结晶高聚物二相分离和结构分析是否可靠，除需考虑分辩结晶相结构参数是否正确的三个判据之外，还需加上二个物理判据.还指出 ,若要获得合理的两相分离结果，提供纯非晶试样的散射曲线作为拟合时本底强度初始值是必要的.     

锌掺杂LaSrCuO铜氧化物的微结构效应

利用Rietveld方法用X射线衍射数据计算了掺Zn的La1.85Sr0.15Cu1-yZnyO4的原子结构参数。随着Zn含量的增加,晶格常数a,b增大,c下降;在Zn含量约0．15处存在一个从四方到正交的结构相变,该相变为二级相变,讨论了Zn掺杂所引起LSCO晶体结构中CuO6八面体对称性的改变,从精修得到的衍射峰形参数计算了各掺杂样品的晶格微应变。     

六方类钙钛矿体系La2Ca2MnO7-Sm2Ca2MnO7的结构变化和相关系

利用柠檬酸盐前驱物法制备了La2-xSmxCa2MnO7系列样品,并利用Rietveld方法对结构进行了精修.结果表明,体系中存在两个单相区(x≤0.8和x≥1.0)和一个两相区(O.8相似文献   

X射线粉末衍射从头晶体结构测定: [Co(NH~3)~5Br]Br~2 配合物的晶体结构

总结了粉末衍射从头晶体结构测定中的问题与对策,并采用常规X射线粉末衍射数据,从头测定了配合物[Co(NH~3)~5Br]Br~2的晶体结构。在指标化与分峰基础上,采用直接法获得含7个独立非H原子的粗结构。在10°～80°(2θ)范围内用3500个强度数据对38个参数作Rietveld精修,得到了[Co(NH~3)~5Br]Br~2的晶体结构。其晶胞参数为a=1.3692(1)nm,b=1.0707(1)nm,c=0.6940(1)nm,V=1.0175(1)nm^3,Z=4。空间群:Pnma,品质因子:M~2~0=49,F~3~0=93(0.0075,43),结构吻合因子:R~p=0.066,R~w~p=0.090,R~F=0.041,R~B=0.042。     

新型无机离子交换剂焦磷亚硒酸锡的结构研究—径向分布函数法

本文报道了应用径向分布函数(RDF)法研究非晶态无机离子交换剂焦磷亚硒酸锡的结构。由RDF的峰位、谷位等数据计算出该化合物中原子间的距离、平均配位数及短程有序畴等。讨论了焦磷亚硒酸锡的结构参数与离子交换剂选择性间的关系。     

Y（1-x）LuxMnO3多铁性陶瓷的制备、相关系和介电性能

采用固态化学反应方法制备了Y(1-x)LuxMnO3体系的系列样品. 利用粉末X射线衍射分析(XRD)和扫描电子显微镜(SEM), 研究了Y(1-x)LuxMnO3体系的样品形貌、相关系和固溶区范围. 采用Rietveld结构精修的方法研究了不同掺杂量对晶体结构的影响, 研究表明, 体系的固溶区范围大约为x=0.0～0.32. 介电性能表明: Lu3+离子的掺杂影响了样品的介电常数和介电损耗, 介电常数在固溶区范围达到最大值, 但掺杂量并未改变居里温度.     

湿化学法合成LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2及其表征(英文)

利用琥珀酸为鳌合剂的湿化学法成功合成了一系列锂离子电池正极材料LiNi1/3Mn1/3Co1/3O2,在合成过程中改变琥珀酸与金属离子摩尔比(R)并研究了这一参数对合成LiNi1/3Mn1/3Co1/3O2材料物理及电化学性质的影响.采用热重、X射线衍射、Rietveld精修、扫描电镜以及超导量子干涉仪对反应机理、材料的结构、形貌以及磁学性质进行了详细表征.得到最佳合成条件为R=1,此时LiNi1/3Mn1/3Co1/3O2的阳离子混排度最低.此外,通过Rietveld精修得到该材料阳离子混排度的结果与通过磁学方法得到的结果定量相符,如对于在R=1条件下合成的样品,Rietveld精修结果显示其阳离子混排度为1.85%,而超导量子干涉仪的测试结果为1.80%.当充放电区间为3.0-4.3V,电流密度为0.2C(1C=160mA·g-1)时,该样品的首次放电容量为161mAh·g-1,库仑效率为93.1%,经过50次循环后,容量保持率可达91.3%.     

Nd:GSAG纳米粉体的合成、晶体结构及光谱

采用共沉淀法,以NH4OH为沉淀剂制备了1％(原子分数)Nd3+:Gd3 Se2 Al3 O12前驱体,并在不同的温度下对前驱体进行煅烧.用X射线衍射(XRD)和红外光谱(FT-IR)技术对前驱体及煅烧后粉体的结构、微观形貌进行了研究.结果表明,前驱体在1000℃下煅烧n获得纯GSAG多晶相粉体.用X射线衍射宽化法估算粉体的平均晶粒尺寸为25 nm.通过X射线粉末衍射,用Rietveld全谱拟合方法对晶体结构进行了精修,得到1000℃下煅烧所得Nd:GSAG粉体的晶胞参数为a=b=c=1.24164(5)nm,α=β=y=90°.在室温下,测定了激发波长为808m的发射谱和检测波长为942 nm的激发谱.另外,测定了 942和1064 nm处的荧光衰减曲线,并用单指数函数进行了拟合,得到对应的荧光寿命分别为0.529和0.512 ms.     

PbF_2:Er~(3+),Yb~(3+)荧光粉的制备和多波长响应双向转换发光机理（英文）

采用高温固相法制备了PbF_2∶Er~(3+),Yb~(3+)双向转换荧光粉。通过X射线粉末衍射分析(XRD)、结构精修分析、功率-强度测试和荧光光谱分析对样品进行了表征。通过X射线衍射和精修结果分析了样品的相组成和晶胞参数的变化。荧光光谱分析表明,在紫外光(378 nm)和不同波长的红外光(808、980、1 064和1 550 nm)激发下,样品在540～550 nm范围内具有强绿光发射和在650～660 nm范围内的弱红光发射。最后,通过强度-功率测试讨论了样品在不同波长的红外光下激发的上转换发光机理,并分析了在378 nm激发的下转换发光机理。     

花状β-氢氧化镍的合成和表征

本文介绍了以大环多胺(六甲基-1，4，8，11-四氮环14-4，11-二烯)的镍(Ⅱ)配合物溶液为反应物，水热水解制备出花状β- Ni(OH)₂亚微米结构，该花状β-Ni(OH)₂由几十个相互连接的纳米片构成。对中间产物的研究结果表明，随着配合物浓度的增加、反应时间的延长，产物形貌从卷曲的片状转变成纳米片组成的花状且花状结构逐渐增密。采用粉末X-射线衍射(XRD)、透射电子显微镜(TEM)和场发射扫描电子显微镜(FESEM)表征了产物，并采用Rietveld精修方法拟合了晶体结构。     

Neutron powder diffraction study of A2BeF4 (A=K, Rb, Cs): Structure refinement and analysis of background

The crystal structure of potassium, rubidium and caesium fluoroberyllates have been re-examined by neutron powder diffraction at room temperature and at 1.5 K. Previously, their structures, obtained from X-ray data, were described in the Pn2₁a space group. However, the results obtained from Rietveld refinements, using powder neutron diffraction, at both temperatures, indicated that all structures are orthorhombic with space group Pnma. The known phase transition at high temperature is probably related to the appearance of a hexagonal pseudo-symmetry instead of the elimination of the mirror plane between the above mentioned orthorhombic space groups. A possible phase transition, at very low temperature, was discarded considering the stereochemical criteria concerning the structural stability of A₂BX₄ compounds. This was confirmed by thermal analysis. On the other hand, a modulated background has been detected in all samples during the refinements. This is compatible with the presence of an amorphous phase, coexisting with the crystalline phase, or with a disordered component within the main crystalline phase. Instead of using a polynomial function, the background was modelled by Fourier filtering improving the fit for all patterns. The radial distribution function (RDF) was obtained from the analysis of the calculated background and compared with the RDF from the average crystal structure. The advantages of neutron with respect to X-ray diffraction were evidenced for this type of compound with β-K₂SO₄-type structure.     

ZrW0.8Mo1.2O8立方相和正交相的微波合成及其表征

Both the cubic and orthorhombic ZrW_0.8Mo_1.2O₈ were prepared by precursor-microwave route. The cubic phase belonged to β-ZrW₂O₈ structure type and the orthorhombic phase was refined with the structural model of LT- ZrMo₂O₈ by the Rietveld method. The orthorhombic phase belonged to Pmn2₁ space group and the cell parameters were a_o=0.597 1(9) nm, b_o=0.730 6(1) nm, c_o=0.912 7(1) nm, R_p%=9.37; wR_p%=11.81. The TEM images were also given. The comparison was made between precursor-heated and precursor-microwave routes. Metastable polymorphic phase was favorably formed by the latter method.     

Two-dimensional Rietveld analysis of celluloses from higher plants

The Rietveld method is a versatile tool to parameterize the fine structure of crystallites analyzed by diffraction. The method relies on a crystallographic model representing what is known a priori, and free coefficients determined from fits to experimental data. This article provides an introduction to Rietveld analysis of celluloses from higher plants that are adequately described by the cellulose Iβ crystal structure. Possibilities of Rietveld analysis have been recently enhanced by a tailored crystallographic model and computational algorithm, named Cellulose Rietveld Analysis for Fine Structure (CRAFS). From each two-dimensional diffraction pattern, CRAFS automated analysis outputs unit cell parameters, crystallite sizes, peak profile functions, integrated crystalline intensity (proportional to cellulose degree of crystallinity), and crystallite orientation distribution function. Two of the major hurdles for analysis of plant cellulose—overlapping of diffraction peaks and preferred crystallite orientation—are consistently treated by the two-dimensional Rietveld analysis. Hence, the method is a unique tool to explore cellulose fine structural variability, with differences arising from specimen conditioning, processing, and biological origins.     

Subsolidus Phase Relations in the ZnO-BaO-V2O5 System

The subsolidus phase relations of the ZnO-BaO-V2O5 ternary systems were investigated by means of X-ray diffraction analysis. There are three ternary compounds, nine binary compounds and sixteen 3-phase regions found in this system. The crystal structure of the ternary compound Ba2ZnV2O8 was refined by Rietveld profile fitting method and the powder diffraction pattern is given. A new ternary compound Ba3.4Zn0.8V4O14.2 has been found by the powder diffraction pattern.     

Characterization of brookite and a new corundum-like titania phase synthesized under hydrothermal conditions

Brookite rich samples were synthesized under hydrothermal conditions by using TiCl₃ as precursor. They also contained a new titanium oxide phase that has the same crystalline structure as Ti₂O₃, and is stable after annealing in air. Samples were characterized with X-ray powder diffraction, transmission electron microscopy and thermogravimetry. Crystalline phases were refined by using the Rietveld method, from which phase concentrations and atomic bond lengths were obtained as a function of sample annealing temperature. Samples contained brookite, anatase, rutile and the new corundum-like phase: Brookite's concentration was larger than 50 wt%, while the one of the corundum-like phase reached 20(6) wt%. The local symmetry and the atomic bond lengths of these two phases depended on the crystallite size; for both, there is a correlation between the evolution of the atomic bond lengths with temperature and their transformation into another phase. The hydrothermal conditions stabilized brookite, anatase, and the corundum-like phase at high temperature: This last phase was stable in air, even at 900°C.     

Structural characterization of ultrasmall superparamagnetic iron oxide (USPIO) particles in aqueous suspension by energy dispersive X-ray diffraction (EDXD)

Ultrasmall superparamagnetic iron oxide (USPIO) particles were structurally characterized in situ in an aqueous dilute suspension by energy dispersive X-ray diffraction (EDXD) and ex situ as powders obtained by lyophilization of the suspension by angular dispersive X-ray diffraction (ADXD) at 20 degrees C. Structural parameters obtained by the Rietveld method on ADXD data were used as starting parameters for modeling the structure of the particles in suspension. Although each particle is a single crystal, as evidenced by conventional X-ray diffraction, our results indicate that the structural order, specific to a crystal, does not extend to the entire volume of the particle. In fact, each individual particle, averagely, has a crystalline structural extension ca. 4.0 nm smaller than the apparent dimensions obtained by both ADXD and TEM (ca. 8.0 nm).     

Hetero-Atom Zeolite (Ⅱ)——Studies on the Crystal Structures of B-Si Pentasil zeolite Molecular Sieves

The crystal structure of B-Si pentasil zeolite molecular sieve was determined by means of the x-ray diffraction for polycrystalline samples and refined by Rietveld method.The parameters of the unit cell are e=19.983(1)A;b=19.773(1)A;c=13.303(1)A.Its space group is D2h1G-Pnma The framework topology found agrees with reported Si-Al ZSM-5zeolite molecular sieves.It is concluded from the structural determination that B is introduced into the framework of this sample.     

High-spin- and low-spin-state structures of [Fe(chloroethyltetrazole)6](ClO4)2 from synchrotron powder diffraction data

The spin-crossover complex [Fe(teec)(6)](ClO(4))(2) (teec = chloroethyltetrazole) exhibits a 50 % incomplete spin crossover in the temperature range 300-30 K. Time-resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high-to-low spin crossover, and the structural characteristics of the high-spin and low-spin models are discussed in relation to other compounds showing a similar type of spin-crossover behavior.