Electronic and elastic properties of the light actinide tellurides

The elastic constants c(11), c(12) and c(44) of U, Np, Pu, and Am telluride single crystals have been obtained by Brillouin scattering from the measur ed sound velocities in prominent crystallographic directions. In case of th e U chalcogenides also by ultrasound techniques. The Cauchy pressure, the P oisson ratio, the anisotropy ratio, the bulk modulus and the Debye temperat ure have been derived from these data. U and Pu telluride have a negative c (12), implying intermediate valence. AmTe has a very low bulk modulus, but a positive c(12). It is extremely soft, with a very low sound velocity. For AmTe also the LO and TO phonon frequencies could be determined. The elasti c data point to a divalent Am state. The optical reflectivity of the light actinide tellurides land sometimes of all chalcogenides) has been measured between UV and infrared wavelengths, in the case of AmTe down to the far in frared. The plasma edge of the free carriers has been determined, which yie lds the ratio of n/m*. Together with the gamma value of the specific heat a nd magnetic data a consistent proposal for the electronic structure of the light actinide chalcogenides can be given. Thus, the Pu chalcogenides are i ntermediate valent and represent the high-pressure phase of the correspondi ng Sm chalcogenides. AmTe, as judged by the electronic, optic and magnetic properties seems to be in the 5f(7) configuration, i.e. divalent Am, but wi th a narrow, half-filled (24 meV) wide 5F band, about 0.1 eV below the bott om of the 6d conduction band. We thus propose a new kind of unhybridized he avy fermion. Also AmTe seems to represent a high-pressure phase of EuTe. (C ) 2001 Elsevier Science B.V. All rights reserved.