1. Topics Appl. Phys.,1983
2. Topics Appl. Phys.,1983
3. H. Vogt: In [3.2], p. 208
4. See, for instance, W. Marshall, S.W. Lovesey: Theory of Thermal Neutron Scattering (Clarendon, Oxford 1971)
5. H. Bilz, W. Kress: Phonon Dispersion Relations in Insulators (Springer, Berlin, Heidelberg 1979)