LNHAL2HN - NEW PHASES IN THE TERNARY-SYSTEM LN/HAL/H (LN = LANTHANOID, HAL = BR, I) .3. PHYSICAL-PROPERTIES

IR and diffuse reflectance spectra, magnetic susceptibility and electrical resistance as well as photoelectron spectra of GdI2Hn and CeI2Hn (n less-than-or-equal-to 1) are reported. GdI2Hn samples with 0 < n less-than-or-equal-to 1 are insulators or semiconductors. Compounds with n = 1 are colourless, with n < 1 blue transparent. Phases with n < 0.9 show metallic lustre. This feature and the electrical properties can be understood on the basis of the electronic structure (Extended Huckel calculations, photoelectron- and reflectance spectroscopy). For n not-equal 1, in contrast to the stoichiometric hydride halides, bands approx. 1 eV below the Fermi edge are populated. With decreasing H content they broaden and the density of states increases. CeI2Hn exhibits a metal-to-semiconductor transition for n almost-equal-to 0.33. According to the susceptibility measurements the ferromagnetic order of GdI2 successively is suppressed by the incorporation of hydrogen. Simultaneously, correlated regions with spontaneous magnetization are maintained. Temperature dependent X-ray diffraction measurements also indicate the existance of such clusters.