Re-examination of the structural properties of solid solutions Sr xCa 1− xCO 3

Abstract

We have re-examined the evolution of orthorhombic cell parameters as a function of the substitution parameter x in solid solutions Sr x Ca 1− x CO 3 in order to clarify contradictory results found in the literature. Calcium carbonate has been synthesized in the presence of Sr 2+ 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 CaCO 3 and strontionite SrCO 3. This result, that is consistent with the existence of continuous solid solutions obeying the Vegard's law in the Sr x Ca 1− x CO 3 system, contradicts previously published assertions.