ROTATIONAL-DYNAMICS OF SOLID C-70 - A NEUTRON-SCATTERING STUDY

PMID: 10011126PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.We report the results of neutron-diffraction and low-energy neutron-inelastic-scattering experiments on high-purity solid C-70 between 10 and 640 K. Thermal hysteresis effects are found to accompany structural changes both on cooling and on heating. The observed diffuse scattering intensity does not change with temperature. At 10 K broad librational peaks are observed at 1.82(16) meV [full width at half maximum=1.8(5) meV]. The peaks soften and broaden further with increasing temperature. At and above room temperature, they collapse into a single quasielastic line. At 300 K, the diffusive reorientational motion appears to be somewhat anisotropic, becoming less so with increasing temperature. An isotropic rotational diffusion model, in which the motions of adjacent molecules are uncorrelated, describes well the results at 525 K. The temperature dependence of the rotational diffusion constants is consistent with a thermally activated process having an activation energy of 32(7) meV.This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K

Glassy carbon, NIST standard reference material (SRM 3600): Hydrogen content, neutron vibrational density of states and heat capacity

© 2018 International Union of Crystallography. Commercial glassy carbon plates being used as absolute intensity calibration standards in small-angle X-ray scattering applications (NIST SRM 3600) have been characterized in several recent publications. This contribution adds to the characterization by measuring the hydrogen content of a plate to be (4.8 ± 0.2) × 10−4(mol H)/(mol C), and by measuring the vibrational spectrum by neutron inelastic scattering. The spectrum bears a strong resemblance to published measurements on graphite, allowing the identification of several spectral features. The measured spectrum is used to calculate the heat capacity of low-hydrogen-content glassy carbon for comparison with measurements reported here from 20 to 295 K