Comparative investigation of elastic diffuse scattering in C-60 powders

C-60 powder samples of varying impurity content have been investigated by neutron scattering techniques. For Q > 2.5 Angstrom(-1) considerable elastic diffuse scattering is found below T-c providing evidence of static disorder in the low-temperature phase. The elastic scattering increases on cooling from T-c to 150 K but remains virtually constant below this temperature. There is no marked dependence on the impurity level. For Q < 2.5 Angstrom(-1) elastic diffuse scattering obeying a [sin(QR)/(QR)](2) law is observed both above and below the phase transition (R is the radius of the C-60 molecule). This scattering is nearly independent of temperature, however, it depends strongly on the amount of impurities in the sample. Model calculations have been performed which relate varying degrees of orientational disorder in C-60 to the elastic scattering observed in powder samples.