Re-examination of the structural properties of solid solutions SrxCa1−xCO3

We have re-examined the evolution of orthorhombic cell parameters as a function of the substitution parameter x in solid solutions SrxCa1−xCO3 in order to clarify contradictory results found in the literature. Calcium carbonate has been synthesized in the presence of Sr2+ ions (Sr/Ca molar ratio ranging from 10−2 to 1), using experimental conditions that previously allowed us to obtain monophasic aragonite. The precipitates obtained have been analysed using powder X-ray diffractometry (XRD) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The powder XRD data confirm the occurrence of purely monophasic strontian-aragonites. Moreover, the cell parameters as well as the substitution parameter x have been refined for 0 < x < 0.5 against powder XRD data through Rietveld refinement. On the other hand, x was deduced from chemical analysis by ICP-AES. The agreement between both techniques is very satisfactory. The evolution of the cell parameters as a function of x is found to be linear within the studied range, this feature being confirmed for the overall domain (0 ≤ x ≤ 1) if one takes into account the cell parameters of aragonite CaCO3 and strontionite SrCO3. This result, that is consistent with the existence of continuous solid solutions obeying the Vegardʹs law in the SrxCa1−xCO3 system, contradicts previously published assertions.