| Popis: |
Starting from Laval's expression for the first-order thermal diffuse scattering (TDS1), a new expression for the inversion temperature of TDS1, Tmax = mΘD2d2hklk/3h2, has been obtained, valid for a crystal of any symmetry. Tmax is attained when (u2)bar above1/2/dhkl = 16%. Every crystalline substance has a definite range where the above formula holds: the upper limit is Tmp and the lower limit is ΘD. The melting temperature defines a dmax for which the inversion phenomenon can be observable. The inversion curves of TDS1 have been calculated for some metallic, ionic and molecular crystals. It is shown that KCl, Pb and Al, for which the inversion phenomenon has been reported, are not special cases. In molecular crystals this effect will be observable mainly at low temperatures. A method is given for determining Debye characteristic temperatures of crystals of any symmetry. This method is tested using Cartz's experimental Tmax for lead. |
