COMPARATIVE INVESTIGATION OF ELASTIC DIFFUSE NEUTRON-SCATTERING IN C-60 POWDER

C-60 powder samples of varying impurity content have been investigated by neutron scattering techniques. For Q greater than or equal to 2.5 Angstrom(-1) (Q = transferred momentum) strong elastic diffuse scatter ing is found below T-c similar to 260 K providing evidence of static d isorder in the low temperature phase. The elastic scattering increases on cooling from T-c to 150 K but remains virtually constant below thi s temperature. There is no marked dependence on the impurity level. Fo r Q less than or equal to 2.5 Angstrom(-1) elastic diffuse scattering obeying a sin(QR)/(QR) law is observed both above and below the phase transition (R = radius of C-60 molecule). This scattering is nearly in dependent of temperature, however, depends strongly on the amount of i mpurities in the sample. In order to account for the unusually strong elastic diffuse scattering intensity model calculations have been perf ormed which relate orientational disorder in C-60 to the elastic scatt ering observed in powder samples.