龙胜滑石矿晶体结构的Rietveld精修

用Rietveld全谱图拟合法精修产自广西桂林龙胜的优质滑石矿的晶体结构,属单斜晶系,空间群为C2/c,点阵常数a=0.5307(19)nm,b=0.9097(15)nm,c=1.8896(1)nm,β=99.1367°(4),z=4。     

Gd2O2SO4粉体的合成及其晶体结构确定

通过750℃,2h煅烧Gd2O3和H2SO4(摩尔比1:1)的前驱体方法合成了Gd2O2SO4粉体.利用Gd2O2SO4的X射线粉末衍射数据和Material Studio 4.0 Reflex模块中Powder solve技术和Rietveld精修方法对Gd2O2SO4的晶体结构进行了研究.研究表明:Gd2O2SO4具有空间群为PMNB(62)的正交晶系,晶胞参数为a=1.2996nm,b=0.8117nm,c=0.4184nm,V=0.440698nm3,Z=4,计算密度为6.6949g/cm3,并确定了晶胞中原子的位置,Rietveld精修得到的Rwp=9.15%.     

化合物LaAlSi的X射线粉末衍射数据

利用X-射线粉末衍射技术和Rietveld结构修正方法对LaAlSi的粉末衍射数据进行了研究，井得到了其X-射线粉末衍射数据。化合物LaAlSi具有α-ThSi2结构类型，空间群为I4 1／amd（No．141），Z=4。点阵参数为a=0．42245（1）nm，c=1．45204（2）nm，衍射峰指标化的可靠性因子F30=211.4（35）。用Rietveld结构修正方法对该化合物晶体结构进行了精化修正，拟合结果为Rp=0．099和Rwp=0．133。     

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.     

YBa_2Cu_3O_7相的不稳定性

本文报道90K 附近超导的 YBa_2Cu_3O_7相在空气中存放时的不稳定性。通过粉末 X 射线衍射研究,证实YBa_2Cu_3O_7相在常温常压下可以与空气中的 CO_2反应生成 BaCO_3     

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。     

Er:YSGG激光晶体的晶体结构和光谱性能

测量了30%(原子分数)Er:YSGG晶体的晶胞参数:a=b=c=(1.24640±0.00065)nm,α=β=γ=90°.用Rietveld方法对X射线衍射谱进行了精修,给出了处于96h位置的O原子分数坐标(x, y, z)=(-0.031433±0.000780、0.058253±0.000792、0.155358±0.000776),并计算了氧配位多面体中的阴阳离子间距和夹角,结果表明Er3 /Y3 处于畸变十二面体的中心.另外还研究了该晶体在室温下的吸收光谱和荧光光谱的性质.在200～1700nm波段内,Er:YSGG晶体吸收谱带主要为Er3 离子的特征吸收,计算了Er3 在966、790nm处的吸收截面;测量了966、790和488nm为激发波长时的室温发射光谱, 当激发波长为966nm时发射谱带强度较大.另外,以1534nm为监测波长得到室温下的激发光谱,研究结果表明Er:YSGG激光晶体适合于InGaAs二极管激光器的泵浦.     

AB2型LaMgNi3.7M0.3(M=Ni、Al、Mn、Co、Sn、Cu)贮氢合金的晶体结构及电极性能

系统研究了LaMgNi3.7M0.3（M=Ni、Al、Mn、Co、Sn、Cu）合金的组织结构和电化学性能。XRD和电子探针显微分析（EPMA）结果表明：该系列合金主相均为LaMgNi4相，其中含Mn、Cu和Co元素在LaMgNia合金相中有一定的固溶度，LaMgNi3.7Sn0.3合金中的Sn元素主要以LaNiSn相析出；XRD全谱拟合分析表明：LaMgNi3.7Al0.3中Al元素主要占据在LaNi5相的3g位置。合会化元素在LaMgNi4相中的固溶度从大到小的顺序是Mn〉Cu〉Co〉Al〉Sn。电化学实验表明，该系列合金经1～3次循环即可活化，最大放电容量由245．2mAh／g（M=Sn）变化至293．2mAh／g（M=Co），但合金电极的循环稳定性均较差。合金电极的高倍率放电性能（HRD900%）从大到小依次为Al〉Sn〉Cu〉Mn〉Ni〉Co，其中氢原子在合金中的扩散时合金电极的高倍率放电性能起主要作用。     

Rietveld法模拟计算金属铀真空热氧化膜物相的含量

在400℃、500℃和600℃下对表面已氧化的金属铀进行真空热氧化退火处理，生成银白色的氧化膜表面。采用、XRD对氧化膜的成分进行了表征，并用Rietveld方法定量分析了金属铀真空热氧化膜中物相的含量。结果表明400℃和500℃时氧化膜主要为U和UO2，600℃时氧化膜中还出现了大量的UC，且U的含量明显增大，UO2含量减少。     

Bi4（SiO4）3晶体结构的X射线粉末衍射研究

在Ｘ射线衍射仪上收集了Ｂｉ_４（ＳｉＯ_４）_３的衍射数据；利用Ｒｉｅｔｖｅｌｄ方法对衍射数据进行指标化，Ｆ_（３０）＝１５８．９０；确定了Ｂｉ_４（ＳｉＯ_４）_３的晶体结构参数。结果发现：该结构中硅氧四面体是变形的孤立四面体，其中两个Ｏ－Ｓｉ－Ｏ键角为１０７．１３°，而另两个为１１４．２６°，详细报道了晶体结构，给出了晶体结构图；提出Ｂｉ离子最外层孤对的６ｓ２电子的存在是形成这种变形配位多面体的原因。     

Structural Anomalies of 1223 Hg(Tl)–Ba–Ca–Cu–O Superconductors in the Temperature Range 100–300 K

The crystal structure of Hg-based 1223 phases, Hg_1–x Tl _x Ba₂Ca₂Cu₃O₈₊, with different oxygen content and Hg/Tl substitution having critical temperature from 114 to 133 K has been investigated by the X-ray powder diffraction technique over the temperature range from room temperature to 100 K. Rietveld analysis results indicate the presence of two different structure anomalies at temperatures 138 and 165K, respectively. The changes in lattice parameters, fractional coordinates, and individual atom thermal parameters near the observed anomalies are discussed.     

丝网印刷工艺制备高T_c Ba-Y-Cu氧化物超导厚膜

本文报道以化学共沉淀法制备 Ba-Y-Cu 氧化物粉料,用丝网漏印技术在兰宝石晶体和氧化铝陶瓷衬底号印刷成膜,经多段温度下的热处理,获得超导转变温度>90K、零电阻温度达84K 以上的超导材料膜。膜层厚度一般为20～50μm。扫描电镜观测表明,材料层致密、气孔很少。时效试验表明膜层超导电性相当稳定。该技术为超导材料膜的器件应用提供了一条途径。     

Study on Fine Structure of Gas Atomized LaNis-based Alloys

The fine structure of hydrogen storage alloy powders MlNi4.3-xCoxMn0.4Al0.3(x=0.75, 0.45, 0.10; Ml: La-rich misch metal) prepared by rapidly solidifying gas atomization was investigated using a Rietveld analysis method. Two sets of CaCus-type crystal constants were observed in the studied alloys and one set was larger than the other. With decreasing powder radius the solidification rate of powder increased, and so did the percentage of a particle part with larger crystal constants. The reason why there were two sets of crystal constants might be the difference of solidification rate between the outside and inside of a particle.     

Study on Fine Structure of Gas Atomized LaNi_5-based Alloys

The fine structure of hydrogen storage alloy powders MlNi_(4.3-x)Co_x Mn_(0.4)Al_(0.3)(x=0.75, 0.45, 0.10, Ml:La-rich mischmetal) prepared by rapidly solidifying gas atomization was investigated using a Rietveld analysis method. Two setsof CaCu_5-type crystal constants were observed in the studied alloys and one set was larger than the other. Withdecreasing powder radius the solidification rate of powder increased, and so did the percentage of a particle part     

A Study on Synthesis Kinetics of YBa_2Cu_3O_x High Tc Superconductor Powder

The synthesis kinetics of YBa_2Cu_30_x supercon-ductor was studied through comparing the calcina-tion (sintering) processes of different kindsof powders. It was shown that the temperatureof synthesis of YBa_2Cu_30_x phase can be loweredfrom 950℃ to 800℃ through direct calcinationof multiphase powder with uniform chemical com-position. The stress which is caused by thevolume change during synthetic reaction breaksthe particles. It facilitates the formationof highly active superfines of superconductor.     

Single Crystals Synthesis and Refinement of the Crystal Structure of the Polymerized Tetragonal Phase of C60

Abstract

The possibilities of single crystals synthesis in conditions of nonisotropic one‐axis contraction were studied. As a result of the work the single crystals of the tetragonal polymerized phase of C₆₀ without orientational domains were obtained. The crystal structure of this phase was resolved using single crystal x‐ray diffraction data. A structural model of this phase proposed early was confirmed and refined to final R = 0.075. The structure is slightly disordered. It consists of a random combination of the P 4 ₂/mmc layers (84%) and of the Immm layers (16%), along the c axis.