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Higher Anharmonic Contributions to Diffuse X‐Ray Scattering
Author(s) -
Reid J. S.
Publication year - 1972
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220520132
Subject(s) - anharmonicity , scattering , boundary (topology) , phonon scattering , halide , order (exchange) , physics , coupling (piping) , phonon , condensed matter physics , chemistry , alkali metal , atomic physics , optics , quantum mechanics , materials science , mathematics , mathematical analysis , inorganic chemistry , finance , economics , metallurgy
An investigation has been made into the importance of higher‐order anharmonic interference terms between the one‐phonon and multiphonon scattering. The second‐order terms are discussed in detail and an exact expression is also given for the general term involving the direct coupling of the one‐phonon and n ‐phonon scattering processes. The most interesting second‐order process has been evaluated directly for the alkali halides NaF, NaCl, NaBr, NaI, KCl, and KBr with the scattering vector lying along [100]. It is concluded that the first‐order term is dominant most of the way to the zone boundary at temperatures up to at least 600 °K. This rapid convergence appears to continue for the third and higher‐order diagrams and these are not expected to contribute significantly to experimental intensities. However, near the zone boundary the second‐order term can be a few percent of the total scattering and hence should be considered.