4f-ELECTRON DENSITY DISTRIBUTION IN CeB₆ AND ITS TEMPERATURE DEPENDENCE. Kiyoaki Tanaka, Chemistry Department, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, 466, and Yoshichika Ohnuki, Physics Department, Osaka University, Machikaneyama-cho, 1-1, Toyonaka 560, JAPAN

The electron density in CeB₆ was measured at 100K, 165K, 230K and 298K and the large peaks on the deformation density map near Ce were first confirmed to be those of 4f-electrons by the X-ray Atomic Orbital Analysis. The results at the four temperatures will be also compared to reveal the origin of the Kondo effect of CeB₆. Rare-earth elements have been widely used in industries and they are also involved in high-temperature super conductors. However the measurement of the f-electron density has been judged to be difficult mainly because of the much severer systematic errors such as absorption, extinction and multiple difffraction(MD) of compounds with heavy atoms. Recently we have demonstrated that the MD could not be neglected in accurate structure factor measurements of crystals with heavy atoms and started the measurement avoiding the MD. The structure factors thus measured at 165K and 100K revealed the large peaks along <100> around Ce. They were analyzed based on the crystal field model utilizing the scattering factors calculated with the relativistic atomic orbitals and confirmed to be those of T1u 4f-orbitals in the Oh crystal field. The deformation density around B corresponds very well to the calculated molecular orbitals of the B₆ molecule and that of CaB₆ composed only of the light atoms, which guarantee the accuracy of the present experiment.