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黄河矿(BaCe(CO)_2F)和氟碳鈰钡矿(Ba_3Ce_2(CO_3)_5F_2)是我国发现的新矿。它们有相同的超结构。前者晶体结构已知。后者只知晶胞参数,原子位置未知,但对其重原子位置有过推测。本文研究了它们的高分辨电子显微象,利用动力学衍射效应测定了氟碳鈰钡矿的晶体结构。矿物是用JEM 108C电子显微镜观察的。从黄河矿过焦系列实验象和计算象的匹配中(图1),发现动力学衍射效应有助于增强轻原子的象衬,并了解到最佳欠焦量为400A,最佳晶体厚度为50A。在此最佳条件下,轻原子可以和重原子一样在象上呈现为黑(图1b,d)。
Yellow Mine (BaCe (CO) 2F) and bastnaesite (Ba_3Ce_2 (CO_3) _5F_2) are new discoveries in China. They have the same superstructure. The former crystal structure is known. The latter only know the unit cell parameters, the atomic position unknown, but its position on the heavy atom speculation. In this paper, their high-resolution electron micrographs were studied, and the crystal structure of barium bastnasite was determined by the kinetic diffraction effect. The mineral was observed with a JEM 108C electron microscope. It is found that the kinetic diffraction effect helps to enhance the image of the light atom as well as the best undercooling quantity is 400A and the optimum crystal thickness is 50A. Under this optimal condition, light atoms can appear as black on the image as heavy atoms (Figure 1b, d).