The high-pressure CaCO3 phase diagram has been the most extensively studied within the carbonates group. However, both the diverse mineralogy of carbonates and the abundance of solid solutions in natural samples require the investigation of multi-component systems at high pressures (P) and temperatures (T). Here we studied a member of the CaCO3–SrCO3 solid-solution series and revealed the effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate.A synthetic solid solution Ca0.82Sr0.18CO3 was studied in situ by Raman spectroscopy in a diamond-anvil cell (DAC) up to 55 GPa and 800 K. The results of this work show significant differences in the high-pressure structural and vibrational behavior of the (Ca,Sr)CO3 solid solution compared to that of pure CaCO3. The monoclinic CaCO3-II-type structure (Sr-calcite-II) was observed already at ambient conditions instead of the “expected” rhombohedral calcite. The stress-induced phase transition to a new high-pressure modification, termed here as Sr-calcite-IIIc, was detected at 7 GPa. Sr-calcite-VII formed already at 16 GPa and room T, which is 14 GPa lower compared to CaCO3-VII. Finally, crystallization of Sr-aragonite was detected at 540 K and 9 GPa, at 200 K lower T than pure aragonite. Our results indicate that substitution of Ca2+ by bigger cations, such as Sr2+, in CaCO3 structures can stabilize phases with larger cation coordination sites (e.g., aragonite, CaCO3-VII, and post-aragonite) at lower P-T conditions compared to pure CaCO3. The present study shows that the role of cationic composition in the phase behavior of carbonates at high pressures should be carefully considered when modeling the deep carbon cycle and mantle processes involving carbonates, such as metasomatism, deep mantle melting, and diamond formation.

中文翻译：

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阳离子取代对碳酸钙中压力诱导的相变的影响

在碳酸盐组中，对高压CaCO3相图的研究最为广泛。然而，碳酸盐的多种矿物学特征和天然样品中固溶体的丰富性都需要研究在高压（P）和温度（T）下的多组分系统。在这里，我们研究了CaCO3–SrCO3固溶体系列的成员，并揭示了阳离子取代对压力引起的碳酸钙相变的影响。通过拉曼光谱法在原位研究了合成的固溶体Ca0.82Sr0.18CO3。高达55 GPa和800 K的金刚石-砧室（DAC）。这项工作的结果表明，与纯CaCO3相比，（Ca，Sr）CO3固溶体的高压结构和振动行为存在显着差异。在环境条件下已经观察到单斜CaCO3-II型结构（Sr-方解石-II），而不是“预期的”菱形方解石。在7 GPa处检测到应力诱导的相转变为新的高压变体（此处称为Sr-方解石IIIc）。Sr-方解石-VII已经在16 GPa和T室形成，与CaCO3-VII相比降低了14 GPa。最后，在540 K和9 GPa下检测到Sr文石的结晶，其T比纯文石低200K。我们的结果表明，与纯CaCO3相比，在较低的PT条件下，CaCO3结构中较大的阳离子（如Sr2 +）取代Ca2 +可以稳定具有较大阳离子配位位点（如文石，CaCO3-VII和后文石）的相。