Characterization of synthetic BaCO3 – SrCO3 (witherite-strontianite) solid-solutions by Fourier transform infrared spectroscopy
Böttcher, Michael E.; Gehlken, Peer-Lennart; Fernández-González, Ángeles; Prieto, Manuel
European Journal of Mineralogy Volume 9 Number 3 (1997), p. 519 - 528
published: Jun 2, 1997
manuscript accepted: Dec 19, 1996
manuscript received: Jan 17, 1996
ArtNo. ESP147050903015, Price: 29.00 €
Abstract The FTIR spectra of l5 synthetic witherite-strontianite (Ba12CO3 - Sr12CO3) solid-solutions containing about l.l atom% 13C, are investigated at ambient temperature and atmospheric pressure for the influence of cationic substitution on the wavenumbers of infrared-active modes of the carbonate ion group between 4000 and 400 cm-1. Homogeneous carbonate solid-solutions, covering the compositional range between 8 and 86 mol% strontium, are grown at 25°C by counter-diffusion through a porous silica-gel transport medium, and the chemical compositions are determined by electron microprobe. As a function of the carbonates chemical composition, an increase in frequency of the fundamental (vl, v2, v3, v4) and combination modes ((vl+v3), (vl+v4), (v3+v4)) with increasing Sr substitution is observed. Nearly linear variations of the frequencies between the end-member values as a function of composition are observed. The FTIR spectrum of Ba13CO3 containing about 1 atom% 12C is measured, too. Due to the substitution of 12C by 13C, the wavenumbers of most of the infrared-active modes are-shifted to lower values, in agreement with theoretical calculations. Measured isotope shift coefficients (vi(13CO32_)/(vi(12CO32_)) are 1.000 (vl), 0.969 (v2), 0.976 (v3), 0.999 (v4), 0.984 (vl+v3), 0.999 (vl+v4) and 0.980 (v3+v4). The isotope shift coefficient observed for v2 of the nearly decoupled carbonate ions containing the respective minor carbon isotope is 0.961.