压电晶体YbBa3(PO4)3的生长与性质表征

压电材料在振动传感器、压力传感器和超声波压电换能器等器件技术领域有着广泛应用,探索新型压电晶体材料用于特种压电传感器件的研发具有重要意义.本文利用传统的提拉法生长出具有高熔点(～1800℃)的磷酸钡镱(YbBa3(PO4)3,YbBP)新型压电晶体.X射线衍射分析表明,该晶体属于立方晶系I 43d空间群,晶胞参数为a=...     

X-ray diffraction and X-ray standing-wave study of the lead stearate film structure

A new approach to the study of the structural quality of crystals is proposed. It is based on the use of X-ray standing-wave method without measuring secondary processes and considers the multiwave interaction of diffraction reflections corresponding to different harmonics of the same crystallographic reflection. A theory of multiwave X-ray diffraction is developed to calculate the rocking curves in the X-ray diffraction scheme under consideration for a long-period quasi-one-dimensional crystal. This phase-sensitive method is used to study the structure of a multilayer lead stearate film on a silicon substrate. Some specific structural features are revealed for the surface layer of the thin film, which are most likely due to the tilt of the upper layer molecules with respect to the external normal to the film surface.     

Determination of Molar Ratio in AB1−x Rocksalt-type Compounds by X-ray Powder Diffraction Method. Application to TiC1−x

The B/A molar ratio in AB_1−x rocksalt-type compounds is determined by X-ray powder diffraction method by measuring of integrated intensities I_hkl. The strategy of measurement is presented to avoid all effects influencing the integrated intensities of X-ray powder diffraction as primary extinction, preferred orientation and surface roughness effect. This paper deals with application of this method to the determination of the deviation from stoichiometry of TiC_1−x compounds.     

Aspects of low heterostructure symmetry in (311)A (In,Ga)As/GaAs

We investigate the structural and optical properties of (In,Ga)As/GaAs heterostructures induced by the low symmetry of the [311]A orientation. High-resolution X-ray diffraction (HRDXD) measurements reveal the existence of a shear-strained unit cell. The onset of relaxation in heavily strained structures leads to pronounced anisotropies and to satellite splittings in the X-ray diffraction patterns. Optical investigations indicate that the impact of the piezoelectric fields on the ground state energy is compensated for by In segregation. Nevertheless these fields cause a pronounced reduction of the excitonic binding energy in the (311)A structures.     

X-ray determination of the polarity of zincblende-structure crystals

An X-ray diffraction procedure for the determination of the polarity of noncentrosymmetric crystals by measuring the integrated reflections of opposite polarity on one surface of the crystal is described. The observed intensities must be corrected for the different asymmetries of the two reflections. To estimate the influence of crystal perfection on the correction factor, the ratios of the integrated reflections were calculated numerically for dynamic diffraction. The method has been applied for determining the polarity of CdTe.     

BiMnO_3改性BNT-BKT压电陶瓷的研究

为了提高BNT基压电陶瓷的电性能,采用传统的陶瓷制备方法,制备了一种Bi基的钙钛矿型无铅压电陶瓷 (1-x)Bi_(0.5)(Na_(0.82)K_(0.18))_(0.5)TiO_3-xBiMnO_3 (简写为BNKT-BMx).研究了Bi基铁电体BiMnO_3对该体系陶瓷微观结构和压电介电性能的影响.结果表明:在所研究的组成范围内陶瓷材料均能够形成纯钙钛矿固溶体,微量BiMnO_3不改变该体系陶瓷的晶体结构,但促进晶粒生长.随着BiMnO_3含量增加,低温介电反常峰消失,高温介电峰出现频率分散性.随BiMnO_3含量增加,压电常数d_(33)和机电耦合系数k_p先增加后降低,在x=0.01时,k_p=0.333,x=0.015时,d_(33)=170 pC/N,为该体系陶瓷压电性能的最优值.     

陶瓷α-Al2O3晶粒度的测定技术分析

本文介绍了电子显微镜、X射线衍射、氮吸附小比表面法、红外光谱结构分析、研磨法等用于陶瓷氧化铝晶粒度测定的情况,通过对比,指出了电子显微镜能够真实地反映微观世界,是多种分析方法的基础.     

Quantitative X-ray diffraction analysis of textured sheet metals

A disadvantage of the quantitative X-ray diffraction analysis of samples from sheet metals is the incorrectness of the measuring results owing to the presence of textures in the material. In considering several reflexes of every phase the influence of textures may be reduced. Such a method will be presented and tested. The yielded results show that the new method can be useful for textured sheet metal samples.     

State-of-the-art and problems of X-ray diffraction analysis of biomacromolecules

The state-of-the-art of X-ray diffraction studies of biomacromolecules is briefly characterized, and the challenge imposed by science is discussed. These studies are characterized by a wide scope and extensive use. This field of science is of great interest and is developed in many countries. The main purpose is to solve practical problems in medicine consisting in the design of drugs against various diseases. X-ray diffraction analysis of enzymes brought the pharmaceutical industry to a new level, thus allowing the rational design of drugs against formerly untreatable diseases. Modern X-ray diffraction studies of biomacromolecules laid the basis for a new science called structural biology. This method allows one to solve fundamental problems of physical chemistry for a new state of matter existing in living systems. Here, science poses numerous problems in analysis of X-ray diffraction data on biological macromolecules. Many of theses problems are in their infancy.     

Ba1-xSrxTiO3薄膜的Sol-gel制备技术与微结构

研究了利用钡、锶的碳酸盐代替醋酸盐作原料,采用新的Sol-gel技术制备Ba1-xSrxTiO3(BST)铁电薄膜的技术.采用碳酸钡、碳酸锶和钛酸四丁酯作原料配制BST溶胶;通过TG/DTA分析确定了BST薄膜的制膜工艺;使用XRD、SEM、AFM技术分析了薄膜的微结构.研究结果表明,采用碳酸盐作为钡、锶的原料,用冰醋酸和乙二醇甲醚混合液作溶剂,可配制出澄清透明、能长时间放置的溶胶,用此溶胶制备出了膜厚均匀、表面光洁致密、没有裂纹的全钙钛矿相的BST薄膜;采用扫描探针显微镜的压电响应模式(PFM)观察到了BST薄膜中的具有纳米结构的a畴和c畴.     

New aspect of diffraction of a highly divergent characteristic X-ray beam

A new way of implementing the diffraction of a highly divergent characteristic X-ray beam has been developed. This method is based on the formation of a diffraction image by the X rays exiting particular (active) points on the crystal surface which lie on hyperbolas. There is a correspondence between the points on the crystal surface and the points in the diffraction image. Local distortions of the crystal structure lead to local deviations of the diffraction lines from proper hyperbolas. This method makes it possible to reveal the block structure of crystals, separate blocks, and estimate the degree of misorientation.     

On the short range atomic structure of non-crystalline carbon

Neutron diffraction data show there isllittle tetrahedral bonding in glassy carbon, and correspond to the Stenhouse-Grout structure factor model for amorphous carbon taking the degenerate case in which the amount of tetrahedral bonding is negligible. This is in contrast to the X-ray results of Noda and Inagaki. Further analysis of the radial distribution function from the neutron diffraction data is presented. A brief summary of other X-ray diffraction measurements on a variety of amorphous carbons is given, all of which confirm the predominantly trigonal coordination. The disagreement of the earlier X-ray and electron diffraction measurements is due to the poor resolution and normalization of the data, and also perhaps the method of preparation. The amount of tetrahedral bonding present in amorphous carbon requires careful diffraction measurements at large scattering vectors to enable better resolution of the peaks in the radial distribution function.     

Numerical separation of background in X-ray diffraction studies

A method for the separation of X-ray background is suggested. The method is based on the integral digital filtration of experimental diffraction patterns and their “smoothening” and the subsequent combination of the smoothened and initial diffraction patterns. The combined diffraction pattern thus obtained is smoothened again, and the whole procedure is repeated anew. The criterion for concluding the iteration procedure (background criterion) is suggested to be the attainment of the situation where a certain percent of the points of the initial diffraction pattern would be below the background line determined. It is shown that, in some instances, the method yields more appropriate results than the traditional methods. The application of the new method is not limited by X-ray diffraction alone.     

High-resolution X-ray diffraction analysis of the Bragg peak integrated intensity in highly mismatched III-N epilayers

A new method of measuring the thickness of GaN epilayers on sapphire (0 0 0 1) substrates by using double crystal X-ray diffraction was proposed. The ratio of the integrated intensity between the GaN epilayer and the sapphire substrate showed a linear relationship with the GaN epilayer thickness up to 2.12 μm. It is practical and convenient to measure the GaN epilayer thickness using this ratio, and can mostly eliminate the effect of the reabsorption, the extinction and other scattering factors of the GaN epilayers.     

Growth and Characterization of Na2CaGe6O14 Single Crystals

Transparent, crack-free Na₂CaGe₆O₁₄ (NCG) single crystals were successfully grown using the Czcchralski technique. The largest crystal had 30 mm in total length and 18 mm in maximal diameter. Best crystal quality was achieved under low temperature gradient arrangement. The crystal structure of NCG has been refined from single crystal X-ray diffraction data. Some piezoelectric properties of NCG are reported.     

The features of identifying lines in a diffraction image formed by a widely divergent X-ray beam

A method for identifying lines in a diffraction image formed by a widely divergent X-ray beam and a technique for measuring the crystal structure parameters in the case of asymmetric crystal position have been developed. It is established that, once the distances between a crystal and a photographic plate and between the points of intersection of the hyperbola branches in a diffraction image are known, one can determine the angle between the crystal’s zone axis and the wave vector, which leads to multiwave diffraction. Relations linking this angle with the parameters of two atomic planes are obtained. It is found that, to measure the parameters of atomic planes belonging to a given zone, one can use different sets of crossed hyperbolas formed by radiations K _α and K _β. The measurements and calculations performed for the same sample (Si crystal), mounted symmetrically and asymmetrically, confirm the reliability of the proposed method.     

Investigation of single crystal growth of GaPO4 by the flux method

GaPO₄ crystals have been grown by a spontaneous nucleation method and the top-seeded solution growth method using three different solvents, 3MoO₃-Li₂O, 3MoO₃-K₂O and 2KPO₃-5MoO₃-3LiF. All of the as-grown crystals were characterized by means of X-ray powder diffraction. The results show that all the crystals were well crystallized and belong to the point group 32, and 2KPO₃-5MoO₃-3LiF flux is the best for nucleation and growth of transparent GaPO₄ crystals. The infrared spectrum of GaPO₄ single crystal obtained by the flux method shows that there is no incorporation of OH groups during the crystallization, which is beneficial for high temperature piezoelectric applications.     

Simulated diffraction on TiN coatings with gradients

A method of computer simulated X-ray diffraction patterns has been applied to TiN coatings assuming different gradients of lattice parameters, microstrain or grain size in the direction normal to the substrate surface. The generated diffraction patterns have been compared with experimental ones and a possibility of real occurrence of such gradients is discussed. This method is superior to the methods based on intensity weighted average quantities which do not take into account actual profiles of diffraction peaks.     

Mathematical simulation and X-ray diffraction investigation of the crystal structure of 1-phenyl-1-<Emphasis Type="Italic">tert</Emphasis>-butyl-3-methyl-1,3-dihydroisobenzofuran

An algorithm for using a priori generation of crystal structures by the discrete modeling method for the interpretation of data obtained from single-crystal X-ray diffraction experiments is considered. The crystal structure of 1-phenyl-1-tert-butyl-3-methyl-1,3-dihydroisobenzofuran is mathematically simulated using the discrete modeling of molecular packings and studied by X-ray diffraction. The simulation is performed for two isomers of the initial chemical compound that are possible from the viewpoint of the mechanism of the chemical reaction used in the synthesis of this compound. Appropriate models that can serve as starting models for solving and refining the crystal structure with the use of X-ray diffraction data are chosen from a complete set of calculated structural models in accordance with specific criteria. The structure is solved using a starting model calculated using the discrete modeling method and refined by the full-matrix least-squares procedure.     

6H-SiC单晶中的微管和小角度晶界

利用透射偏光显微术、同步辐射X射线形貌术、高分辨X射线衍射方法对6H-SiC(0001)晶片中的微管和小角度晶界等缺陷进行了研究.实验发现,在透射偏光显微镜下,微管通常呈现为蝴蝶形,这是由于微管周围存在着应力场,且应力分布不均匀,当线偏振光在通过微管周围区域时传播速度不同造成的.从X射线背反射同步辐射形貌像得到晶片中微管的Burgers矢量大小在2c到10c之间.从晶片00012衍射的双晶衍射摇摆曲线可以看出,晶片的中间大部分区域质量很好,双晶衍射峰为单峰且半峰宽很窄,一般为35"左右.在外围区域双晶衍射峰的半峰宽变宽,有些区域还会出现衍射峰的分裂,这说明外围区域有嵌镶块结构存在.