The form of the effective anharmonic one-particle potential up to quartic terms is given and the expression of the temperature factor is derived for atoms occupying the sites of the point-group symmetry 6m2. The theory is applied to the analysis of the elastic thermal-neutron scattering data from a single crystal of Zn measured at 295 K and corrected for extinction and inelastic scattering contamination. The data show significant quartic terms. The values obtained for the anharmonic potential parameters correspond to the mean-square amplitudes (u 2) =0-0114 (3) A 2 and (u 2) =0.0257 (5) A 2 of the atomic vibrations in the principal directions. The present results are compared with other recent determinations. The discrepancy of the experimental values with theoretical calculations can be accounted for in full by constant-volume anharmonic effects.

No abstract

A readily applicable procedure is presented for calculating the contribution of one-phonon scattering (TDS) to measured integrated intensities for single crystals of any symmetry under conventional experimental situations. The anisotropy of the scattering is included correctly within the continuum elasticity approximation. A computer program is presented for the calculation of TDS contribution for cubic, tetragonal, orthorhombic, hexagonal and trigonal crystal structures. The procedure is applied to the calculation of the one-phonon contribution for the hexagonal and tetragonal crystal structures.

Site symmetrized expressions of the atomic temperature factor for all crystallographic point groups have been derived within the framework of the effective one-particle potential formalism. The formulation makes use of the harmonic oscillator eigenfunctions leading to Fourier invariant expressions for the probability density function. The present formalism lends itself for a straightforward application to any crystal structure. The treatment is applied to the analysis of recent neutron diffraction data on zinc. The results are found to be in full accord with those obtained by the use of earlier formalisms.