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Internal Strains and Raman‐Active Optical Phonons
Author(s) -
Anastassakis E.,
Cardona M.
Publication year - 1981
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.2221040223
Subject(s) - phonon , raman spectroscopy , crystal (programming language) , symmetry (geometry) , diffraction , atom (system on chip) , position (finance) , strain (injury) , condensed matter physics , tensor (intrinsic definition) , crystallography , stress (linguistics) , physics , molecular physics , materials science , chemistry , optics , geometry , mathematics , computer science , medicine , finance , economics , embedded system , programming language , linguistics , philosophy
The connection between internal strains and Raman‐active optical phonons in crystals is discussed. In crystals with more than one atom per unit cell, there is usually a number of atomic position parameters which cannot be uniquely defined by crystal symmetry arguments. Within the present scheme, it is shown that those parameters correspond to the number of fully symmetric (Γ 1 , A 1 ) optical phonons at q = 0. Besides lowering the symmetry of the crystal, an external stress can introduce new atomic position parameters (internal strains). The criteria are given for determining the type of internal strain which may be produced by an external stress. The internal strain is looked upon as a “frozen” Raman‐active phonon, both belonging to the same irreducible representation of the crystal point group. It is shown that the well‐known matrices of the Raman tensor can be used directly to determine the selection rules for the stress‐induced internal strains in all crystals, regardless of symmetry. Related unit cell crystal parameters can be determined with X‐ray diffraction techniques.