Mean-square atomic displacement and antisymmetric atomic vibrations in beryllium at room temperature determined from short-wavelength neutron data

The atomic vibrations in metallic beryllium at 295 K are determined from single-crystal neutron diffraction data corrected for thermal diffuse scattering, second-order contamination and extinction effects. Full sets of data were collected from two single crystals of volumes 8 and 27 mm3, using wavelengths of 0.525 and 0.425 Å, respectively. Data extend to sin θ/λ = 2.1 Å-1. The room-temperature values of the principal components of the mean-square atomic displacement are (u2x) = 0.00594 (3) Å2 in the basal plane and (u2z) = 0.00537 (3) Å2 along the 63 axis of the hexagonal cell. These values are compared with earlier and very recent X-ray determinations. The vibrational anharmonicity expressed as the third cumulant is C112 = 0.0008 (1) Å3.