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Application of Small-Crystal Diffraction Technique Using Synchrotron Radiation to Structural Studies of Ceramics

同步辐射小晶体衍射技术在陶瓷结构研究中的应用

基本信息

批准号：
07555191
负责人：
ISHIZAWA Nobuo
金额：
$ 2.5万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Both experimental and theoretical approaches to the cahrge density distribution study become more important in the field of materials science. However, several kinds of effects limit the accuracy of the observed kinematical structure factors from imperfect crystals. They are extinction, multiple scattering, absorption, counting statistics, thermal diffuse scattering, etc. The extinction and absorption can be reduced significantrly by using a smaller crystal and/or a shorter wavelength. Since both solutions tend to decrease the diffracted intensities, the use of synchrotron radiations is strongly recommended for accurate structure analyzes.In this study, we employed an improved single crystal diffraction technique to overcome the problems mentioned above. The technique has features of (1) using a small crystal of about 10mm in size, (2) using a vertically polarized synchrotron radiations at the beam line 14A equipped with a horizontal-type four-circle diffractometer suitable for the charge density study.Promising results have come out. For example, the three-dimensional diffraction data from a K_2NiF_4-type CaYAlO_4 single crystal of about 10mm in size have been found to be scarcely affected by the secondary extinction with a minimum value for the secondary extinction transmission factor Ys of 0.988 for the 200 strongest reflection. The value should be compared to 0.5855 calculated for a spherical specimen with diameter of 112mm mounted on the Ag rotating-anode four-circle diffractometer. The analysis of the extinction-free data on CaYAlO_4 provided detailed information about the composition, atomic positions and the electron density distribution, which have never been obtained by the conventional methods.Various structural studies were performed successfully on ceramic materials, such as BaTiO_3, lead-containing relaxr materials, CuInSe_2, MnS_2, LaTa_3O_9, LaNb_3O9 rare-earth sesquioxides, etc.

实验方法和理论方法对电荷密度分布的研究在材料科学领域变得越来越重要。然而，几种影响限制了从不完美晶体中观察到的运动结构因素的准确性。它们是消光、多次散射、吸收、计数统计、热扩散散射等。通过使用更小的晶体和/或更短的波长，可以显著减少消光和吸收。由于两种方法都会降低衍射强度，因此强烈建议使用同步辐射进行精确的结构分析。在本研究中，我们采用了一种改进的单晶衍射技术来克服上述问题。该技术具有以下特点：(1)使用尺寸约为10mm的小晶体，(2)在波束线14A处使用垂直偏振同步辐射，并在波束线14A处配备适合电荷密度研究的水平四圆衍射仪。有希望的结果已经出来了。例如，尺寸约为10mm的k_2nif_4型CaYAlO_4单晶的三维衍射数据几乎不受二次消光的影响，200次最强反射的二次消光透射系数Ys最小值为0.988。该值应与安装在Ag旋转阳极四圆衍射仪上的直径为112mm的球形试样计算的0.5855进行比较。对CaYAlO_4无消光数据的分析，提供了常规方法无法得到的有关CaYAlO_4的组成、原子位置和电子密度分布的详细信息。对BaTiO_3、含铅弛豫材料、CuInSe_2、MnS_2、LaTa_3O_9、LaNb_3O9、稀土半氧化物等陶瓷材料进行了各种结构研究。