| Research Abstract |
We adopted GaAs as an typical material of two-atomic crystals and tried an independent determination of the temperature factor of Ga atom in a powder sample. This project was started in 1988 with a Grant-in-Aid for Scientific Research (B) and we applied for the grant to improve the accuracy of measurement of diffraction intensity. We have carried out diffraction measurements at 2 pairs of wavelengths on the longer and shorter wavelength sides of K-absorption edge(1.19580A) of Ga atom and at 2 wavelengths on the longer wavelength side, at the Photon Factory of the National Laboratories for High Energy Physics, this year. After the reception of the grant we could have only one machine time when we carried out diffraction measurements at 1.19857 and 1.19332 A. We can get the temperature factor of 3.5A^2 from the pairs of measurements at longer and shorter sides of the K-edge, which contains much error refering to atomic distance of 2.45A and also compared with the factor 0.916A^2 obtained at Cuk alpha 1 by means of the conventional method, mainly because of low accuracy at the shorter wavelength side.
Since the accuracy of measurements at longer wavelength side is comparatively high, the temperature factor was estimated from fairs at longer side where difference in f'_G is enough to estimate the temperature factor of Ga and the difference in f"_G can be neglected. In this method the atomic scattering factor of Ga is necessary and the obtained value was 1.3A^2, which is also larger than 0.916A^2. However, f'_G and f"_G are calculated from contributions of K and L electrons, so that the factor 1.3A^2 corresponds to the vibration of the ion core, whereas 0.916A^2 corresponds to the vibration of atom as a whole under the assumption of a rigid atom. The real Ga atom is not so rigid that the vibration of the ion core can be larger than that of the whole atom. The result of 1.3 A^2 may be reasonable and can be the result of vibration of the ion core.
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