Phonon resonances and infrared absorption due to interstitial F− ions and substitutional trivalent cations

1980 ◽  
Vol 58 (6) ◽  
pp. 803-811 ◽  
Author(s):  
M. A. H. Nerenberg ◽  
J. Govindarajan ◽  
P. W. M. Jacobs ◽  
T. M. Haridasan
Keyword(s):  
Absorption Coefficient ◽  
Absorption Spectra ◽  
Infrared Absorption ◽  
Reasonable Agreement ◽  
Interstitial Site ◽  
Trivalent Cation ◽  
Site Symmetry ◽  
Function Formulation ◽  
Trivalent Cations ◽  
Infrared Absorption Spectra

A Green's function formulation is developed to compute the phonon resonances of an F− interstitial perturbed by the presence of a trivalent cation which occupies one of the second neighbour sites of the interstitial in BaF2, the interstitial site symmetry being thereby reduced from Oh to C4v. Expressions for the absorption coefficient are obtained for the case of an isolated interstitial and for that of the interstitial with an adjacent trivalent cation. These expressions are evaluated for both the isolated interstitial and for Fi− associated with Y3+, Gd3+, or La3+. There is reasonable agreement between theory and the experimentally observed infrared absorption spectra measured by Morlot, Hadni, Villermain-Lecollier, and Strimer.

Study of decreased T site-symmetry in the mixed crystals Ag3(PO4,AsO4)

1980 ◽  
Vol 45 (12) ◽  
pp. 3262-3265 ◽  
Author(s):  
Alexander Muck ◽  
Jindřich Čáp ◽  
Bohumil Hájek
Keyword(s):  
Absorption Spectra ◽  
Infrared Absorption ◽  
Factor Group ◽  
Mixed Crystals ◽  
Site Symmetry ◽  
X Ray ◽  
Powder Samples ◽  
Substitution Type ◽  
Infrared Absorption Spectra ◽  
Effective Site

The system Ag3PO4-Ag3AsO4 has been studied by X-ray analysis of the powder samples and infrared absorption spectra. Formation of cubic mixed crystals of the substitution type has been found within the whole concentration range. For the tetrahedral anions at the site T(2) lowering of the site-symmetry to the effective site-symmetry C3 has been found on the basis of the site-and factor-group analyses of the space group Td4.

The infrared absorption spectra of mixed Ag3[AsO4, VO4] crystals

1979 ◽  
Vol 44 (11) ◽  
pp. 3346-3349 ◽  
Author(s):  
Bohumil Hájek ◽  
Alexander Muck ◽  
Olga Smrčková
Keyword(s):  
Absorption Spectra ◽  
Infrared Absorption ◽  
Factor Group ◽  
Mixed Crystals ◽  
Site Symmetry ◽  
Lattice Vibrations ◽  
Space Group ◽  
Infrared Absorption Spectra ◽  
Effective Site

Mixed Ag3[AsO4, VO4] crystals were prepared over the whole concentration range. In the 0-40% mol. Vanadate concentration range the mixed crystals are isostructural with Ag3AsO4 (T4d, Z = 2). Site- and factor group analyses were carried out for this space group and structure. Above 60 mol% vanadate, the mixed crystals are tetragonal with Ag3VO4 structure. It follows from the behaviour of the ν4AsO3-4 vibration that, in cubic mixed crystals with 40 mol% Ag3VO4, the site-symmetry T is reduced to effective site-symmetry C3 by the effect of lattice vibrations of the T(F) and R(F) types.

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