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Directional Dispersion of the Phonon Modes in Optically Uniaxial Solids, Far‐Infrared Reflection Spectra, Dielectric and Optic Constants, Dynamic Effective Ionic Charges of the Defect Chalcopyrites CdGa 2 S 4 , CdGa 2 Se 4 , HgGa 2 S 4 , and HgGa 2 Se 4
Author(s) -
Haeuseler H.,
Wäschenbach G.,
Lutz H. D.
Publication year - 1985
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.2221290212
Subject(s) - phonon , materials science , spectral line , ionic bonding , dielectric , anisotropy , condensed matter physics , dispersion (optics) , far infrared , dispersion relation , reflection (computer programming) , infrared , optics , molecular physics , chemistry , optoelectronics , physics , ion , organic chemistry , computer science , programming language , astronomy
The polarized far‐infrared reflection spectra of single crystals of the defect chalcopyrites CdGa 2 S 4 CdGa 2 Se 4 , HgGa 2 S 4 , and HgGa 2 Se 4 grown by vapour phase transport technique are presented in the range from 40 to 600 cm −1 . The spectra reveal ten reststrahlen bands as predicted by group theoretical treatment. The oscillator parameters ε α∞ , ω αf , ω αf , and γ αf , the transverse and longitudinal optical phonon frequencies ω TO and ω LO , and the dynamic effective ionic charges are calculated using classical oscillator fit method. The high‐frequency dielectric constants ε α∞ show an anisotropic behaviour, the effective charges (Szigeti charges), however, are approximately scalar quantities. From the obtained oscillator parameters the directional dispersion of the extraordinary polar phonons is determined. The reflection spectra calculated for oblique phonons are discussed and compared to those of pellets hot‐pressed from polycrystalline samples.