Abstract
The wavelength derivative Raman scattering spectra of KBr: Tl and KCl: Tl at 90 K are interpreted in detail in terms of scattering by phonons at Van Hove critical points of the host crystal. In this interpretation the line shape is used as one of the criteria, together with energy and selection rules, in identifying an experimental structure with a critical point. In addition to critical points which are symmetry required and on symmetry lines, we find several critical points which have a symmetry of only one mirror plane. It is shown that the largest structure of each of the spectra results from scattering by phonons on a critical or almost critical line. Such critical lines exist in many rock-salt crystals but not in all. The conditions for the existence of a critical line are discussed.
Original language | English |
---|---|
Pages (from-to) | 2918-2924 |
Number of pages | 7 |
Journal | Physical Review B |
Volume | 18 |
Issue number | 6 |
DOIs | |
State | Published - 1978 |