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The Effect of Short‐Range Order on the Vibrational Spectra of 3:2 Coordinated Chalcogenide Glasses. Analysis of the Vibrational Spectra by Using Pyramidal Structural Units
Author(s) -
Giehler 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.2221060122
Subject(s) - electronegativity , raman spectroscopy , chalcogenide , chemistry , lone pair , molecular vibration , valence electron , atom (system on chip) , chalcogen , valence (chemistry) , molecular physics , crystallography , electron , molecule , optics , physics , organic chemistry , quantum mechanics , computer science , embedded system
Infrared reflection and Raman spectra of 3:2 coordinated chalcogenide glasses are analysed by fitting the optical spectra using a dielectric function consisting of four oscillator terms. The obtained frequencies and infrared intensities of the major infared and Raman vibrational bands are studied within the framework of one aspect of the short‐range order of 3:2 glasses—pyramidal structural units. It is shown that in this model the frequencies of the major vibrational modes (with the exception of As 2 O 3 ) of all 3:2 chalcogenide glasses can be well explained if one takes into account chemical trends (i) in the force constants (in such a way that the stretching force constant is inversely proportional to the third power of the bond length) and (ii) in the bond angle of the apex atom of the pyramid (in such a way that an increasing electronegativity of the apex atom with respect to that of the chalcogen atom causes mostly an increase of the bond angle at the apex atom). For an understanding of the major vibrational properties of As 2 O 3 glass the vibrational coupling of the pyramidal stuctural units with each other especially due to the high electronegativity and the light mass of the oxygen atom) must be taken into account. The Penn gap energies and ionicities of 3:2 coordinated chalcogenide glasses are determined within the approximation that each pyramidal structural unit contributes eleven valence (including lone‐pair) electrons to the chemical bonding. The chemical trend in the intensities of the major infrared vibrational bands characterized by the effective charges is explained as due to a trend in the ionicities of the studied glasses.