. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Diffraction pattern of PbTe layer. Fig. 2. PbTe layer exposed to intense electron beam during 10-20 seconds. Magnification 6000. Fig. 3. PbTe layer exposed to intense electron beam longer than 20 seconds. Magnification 6800. rings of the NaCl type structure, the intensity of which is determined by the difference of atom factors. Thus, a crystal lattice of the kind proposed shows an electron diiTraction pattern corresponding to simple cubic structure with the lattice constant halved. Of the three analogous
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Diffraction pattern of PbTe layer. Fig. 2. PbTe layer exposed to intense electron beam during 10-20 seconds. Magnification 6000. Fig. 3. PbTe layer exposed to intense electron beam longer than 20 seconds. Magnification 6800. rings of the NaCl type structure, the intensity of which is determined by the difference of atom factors. Thus, a crystal lattice of the kind proposed shows an electron diiTraction pattern corresponding to simple cubic structure with the lattice constant halved. Of the three analogous compounds PbS, PbSe and PbTe, the properties of PbS are the best known. Hxperimental data and a theoretical analysis (1) prove this compound to be only slightly ionic in character. The lesser difTerence in atomic numbers of the components in PbTe should cause the ionic properties to recede still further. These considerations should make the authors' assumption of the Pb and Te atoms replacing each other in the crystal lattice points seem more plausible. The PbTe layers were also examined with the electron microscope. When magnified 10,000 times they appeared to be homogeneous. Following illumination with an intense electronic beam for 10- 20 seconds the layer underwent changes: small crystals formed, at first very minute in size, and later on separate, scantily distributed crystals at- taining 1000 A (fig. 2). Further illumination caused gaps in the layer (fig. 3). The authors wish to express their gratitude to Professor L. Sosnowski for his valuable discussions in interpreting the results. References 1. Bfll. D. C, Hum, D. M., Pinchfrle, L., Sciama, D. W., and Woodward, P. M., Proc. Roy. Soc. A, 217, 71 (1953). 2. Checinska, H. and Sosnowski, Bull. Acad. Polon. Sci., CI. Ill, 383 (1954). 3. Wyckoff, Crystal Structures. Interscience. New York 1953. I(dentification of Minerals Present in Mine Dusts by Electron DifTraction an(J Electron Microscopy J. H. Talbot Research Labor
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