A neutron powder investigation of the structure of KCaCO3F at various temperatures

Denticity and Mobility of the Carbonate Groups in AMCO3F Fluorocarbonates: A Study on KMnCO3F and High Temperature KCaCO3F Polymorph

“…However, the DTA curve of KCaCO 3 F provided by Sun et al. clearly demonstrates an endothermic peak at ∼330 °C (Figure in ref ), in agreement with our findings. We can speculate that the source of these disagreements might originate from slight difference in chemical composition of the samples: Sun et al have reported uncontrolled contamination of their samples by silicon during the synthesis.…”

“…A remark should be made on obvious discrepancy between our observation of the temperature-dependent structure evolution of KCaCO 3 F and the report from Sun et al, where no structural transition has been observed by neutron powder diffraction in the 295–673 K temperature range . However, the DTA curve of KCaCO 3 F provided by Sun et al.…”

“…The room temperature PXRD pattern is indexed with a hexagonal unit cell with the space group P6̅ m2 and lattice parameters a = 5.09338(4) Å and c = 4.44935(4) Å, and the Rietveld refinement from the NPD pattern at RT (Figure S2, Tables S5−S8) confirms full agreement of the RT-KCaCO 3 F structure with the previous reports. 1,11,12 Heating the sample up to 300 °C (Figure 5, blue patterns) does not change the crystal structure. However, at around 320 °C we observe the coexistence of two phases (Figure 5, black pattern).…”

“…Among this family, KCaCO 3 F, ASrCO 3 F (A = K, Rb) and APbCO 3 F (A = Rb, Cs) adopt the hexagonal cell of smallest volume, which can be selected as the basic unit cell for the whole series (Figure ). ,,, In these compounds all carbonate groups are crystallographically identical and coordinate the M cations with two oxygens acting as bidentate ligands. In ACaCO 3 F (A = Rb, Cs) one-third of the carbonate groups are rotated by 60° around the c axis facing one of its oxygens toward the M cation, thus becoming a monodentate ligand .…”

Crystal structures of carbonates Cs2Sr2(CO3)3 and Rb2Sr2(CO3)3 from powder data

“…For such cases, the use of neutron diffraction is generally preferred. Strong interaction of neutron with nuclei (rather than the diffuse electron cloud) enables neutron diffraction to locate light atoms (e.g., hydrogen) in the presence of heavier ones (Troyanov et al , 2002) and to distinguish neighboring elements more easily (Sun et al , 2006).…”