Publication: Análisis de la solución sólida sintética Aragonito-Estroncianita mediante espectroscopía vibracional (Infrarrojo y Raman por transformada de Fourier)
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1997
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Sociedad Española de Mineralogía
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Abstract
El presente trabajo aborda el estudio mediante espectroscopía vibracional (Infrarrojo dispersivo y Raman por transformada de Fourier) de una serie de muestras sintéticas de la solución sólida aragonito-estroncianita. Además de los dos miembros extremos, son analizadas nueve muestras intermedias cuyas composiciones varían de modo uniforme entre Ca0,9Sr0,1CO3 y Ca0,1Sr0,9CO3). Se realiza un examen detallado de los modos internos del anión carbonato empleando el análisis del perfil de las bandas y el subsecuente ajuste de los distintos componentes. La incorporación aleatoria del segundo catión genera visibles fenómenos de desorden posicional con el consecuente incremento (hasta casi duplicarse) de la semianchura de ciertas bandas vibracionales. De particular interés son los resultados obtenidos en los modos doblemente degenerados (tensión y flexión antisimétricas, v3 y v4) con la aparición de tres componentes en la banda de tensión en el espectro infrarrojo y otros tres en la banda de flexión del espectro Raman, asignados respectivamente a un sobretono del modo de flexión en posible resonancia de Fermi con el fundamental de ensión y a una escisión Davidov. El análisis de las bajas frecuencias de los espectros Raman-TF es revelador de una cohesión entre las capas catión/carbonato/cation más débil en el aragonito(sint) que en la estroncianita(sint).
Synthetic aragonite-strontianite solid-solution samples have een studied using dispersive Infrared and Fourier transform Raman spectroscopy. Besides the end-members, nine samples whose range of composition covers evenIy from CaO.9SrO,1CO3 to CaO,1SrO.9CO3 were analysed. Carbonate anion internal modes are examined in detail by means of band-shape analysis and component fitting procedures. Positional disorder induced by the random cationic substitution determines strong increases of the halfwidth in several vibrational bands. Results obtained for the doubly degenerated modes (antisymmetric stretching and bending, v3 and v4) reveal the presence of three components either in the Infrared antisymmetric stretching band as well in the Raman antisymmetric bending bando These findings are interpreted in terms of an overtone 2v4in possible Fermi resonance with the corresponding v3 fundamental in the Infrared spectra, and the presence of a Davidov (factor group) splitting in the FT-Raman v4 bando Lattice modes in the FT- Raman spectra emonstrate weaker cohesion between the cation/carbonate/cation layers in aragonite(sinth} than in strontianite (sinth).
Synthetic aragonite-strontianite solid-solution samples have een studied using dispersive Infrared and Fourier transform Raman spectroscopy. Besides the end-members, nine samples whose range of composition covers evenIy from CaO.9SrO,1CO3 to CaO,1SrO.9CO3 were analysed. Carbonate anion internal modes are examined in detail by means of band-shape analysis and component fitting procedures. Positional disorder induced by the random cationic substitution determines strong increases of the halfwidth in several vibrational bands. Results obtained for the doubly degenerated modes (antisymmetric stretching and bending, v3 and v4) reveal the presence of three components either in the Infrared antisymmetric stretching band as well in the Raman antisymmetric bending bando These findings are interpreted in terms of an overtone 2v4in possible Fermi resonance with the corresponding v3 fundamental in the Infrared spectra, and the presence of a Davidov (factor group) splitting in the FT-Raman v4 bando Lattice modes in the FT- Raman spectra emonstrate weaker cohesion between the cation/carbonate/cation layers in aragonite(sinth} than in strontianite (sinth).