Structural, Physical, and Thermodynamic Properties of Aragonitic CaxSr1–xCO3 Solid Solutions

Single-phase CaxSr1–xCO3 solid solutions with an aragonite structure and x = 0–1 were obtained by precipitation synthesis and characterized with respect to their structural, physical, and thermodynamic properties. While there is no measurable excess volume of mixing, relaxation microcalorimetry showed a noticeable excess enthalpy of mixing, ΔH298ex. While the values determined here are much smaller than those obtained in an earlier study by solution calorimetry, they are consistent with the results of density functional theory (DFT)-based calculations. A combination of Raman spectroscopy and atomistic modeling confirms the finding based on the analysis of the diffraction data that there is no ordering of the Ca and Sr atoms. For the atomistic models, both quasi-random special structures and the virtual crystal approximation were employed. The dependence of the bulk modulus on composition was obtained by fitting an equation of state (EOS) to high-pressure synchrotron powder diffraction data and by DFT-based calculations, where stress–strain and compression data were employed. Both, the experimental and the DFT pressure-dependent data show an anomalous pressure-induced elongation of the b-axis around 20–30 GPa, depending on composition, but no structural pressure-induced phase transition until 40 GPa, the highest pressure investigated here.