Crystal structure of norsethite-type BaMn(CO3)2 and its pressure-induced transition investigated by Raman spectroscopy

• DOI: 10.1007/s00269-019-01038-w
• Publication Date: 2019-05-30T12:02:32Z
• Authors: Wen Liang; Lin Li; Yuan Yin; Rui Li; Zeming Li; Xiqiang Liu; Chaoshuai Zhao; Shuguang Yang; Yong Meng; Zengsheng Li; Yu He; Heping Li
• Keywords: Superstructure; Crystal (programming language); Space group

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 Ba1.0Mn1.0(CO3)2. Accurate crystalline structural data were determined from single crystal X-ray diffraction (XRD). The $$R\overline{3} c$$ space-group with a doubled c-axis and $$R\overline{3} m$$ space-group were used to refine the crystal structure of BaMn(CO3)2. It is proved that $$R\overline{3} m$$ 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) A and c = 17.2797(10) A in the rhombohedral symmetry of the $$R\overline{3} m$$ 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 ( $$\frac{{{\text{d}}\nu_{i} }}{{{\text{d}}P}}$$ ) were quantified. Each Raman vibration underwent resolvable splitting and the corresponding $$\frac{{{\text{d}}\nu_{i} }}{{{\text{d}}P}}$$ showed a pronounced jump as the pressure reached 3.8 GPa arising from a pressure-induced transition.