中国科学院地球化学研究所机构知识库

Single crystals of norsethite-type carbonate BaMn(CO₃)₂ up to 200 μm in size were synthesized in a closed cavity under high pressure–temperature (P–T) conditions. Electron microprobe analyses revealed the composition of 49.00–49.09 wt% BaO and 22.66–22.74 wt% MnO, which correspond well to the ideal formula of Ba_1.0Mn_1.0(CO₃)₂. Accurate crystalline structural data were determined from single crystal X-ray diffraction (XRD). The R3¯¯¯cR3¯c space-group with a doubled c-axis and R3¯¯¯mR3¯m space-group were used to refine the crystal structure of BaMn(CO₃)₂. It is proved that R3¯¯¯mR3¯m is the most probable space-group for the BaMn(CO₃)₂ crystal structure because no superstructure reflections were observed in the X-ray images. The unit cell parameters were identified to be a = 5.0827(2) Å and c = 17.2797(10) Å in the rhombohedral symmetry of the R3¯¯¯mR3¯m space-group with a final R-value of 0.0184. High-pressure Raman spectroscopy was performed up to 10 GPa at room temperature, and Raman band shifts (dνidPdνidP) were quantified. Each Raman vibration underwent resolvable splitting and the corresponding dνidPdνidP showed a pronounced jump as the pressure reached 3.8 GPa arising from a pressure-induced transition.