Abstract
A re-investigation of the crystal structure of tricalcium cobalt(II) tetra-aluminate, Ca3CoAl4O10, using single-crystal X-ray diffraction data, revealed ortho-rhom-bic (Pbcm) symmetry. The present contribution corrects the results of a previous X-ray powder diffraction study [Vazquez et al. (2002 ▸). J. Solid State Chem. 166, 191-196] where this phase has been described in an unnecessarily low space-group symmetry (Pbc21). The compound belongs to the group of tetra-hedral framework structures. The distribution of the aluminium and cobalt ions among the centres of the four different tetra-hedra within the asymmetric unit has been studied in detail. Charge compensation is achieved by the incorporation of two symmetrically independent calcium ions located in voids of the tetra-hedral framework. Ca3CoAl4O10 is isotypic with Ca3MgAl4O10.
Highlights
In a recent paper on the phase relationships in the system CaO–MgO–Al2O3, we reported the existence and the crystal structure of Ca3MgAl4O10 (Kahlenberg et al, 2018), a phase of interest for slags occurring in secondary refining processes in metallurgy or refractories, for example
The major difference from our investigation on Ca3MgAl4O10 results from the fact that the previous study attributed Ca3CoAl4O10 to the acentric space group Pbc21, while Ca3MgAl4O10 crystallizes in the centrosymmetric space group Pbcm
For the former compound the description in an acentric space group has to be scrutinized
Summary
A re-investigation of the crystal structure of tricalcium cobalt(II) tetraaluminate, Ca3CoAl4O10, using single-crystal X-ray diffraction data, revealed orthorhombic (Pbcm) symmetry. The major difference from our investigation on Ca3MgAl4O10 results from the fact that the previous study attributed Ca3CoAl4O10 to the acentric space group Pbc, while Ca3MgAl4O10 crystallizes in the centrosymmetric space group Pbcm. For the former compound the description in an acentric space group has to be scrutinized. The distribution of the cobalt and aluminium ions on the different T sites is another difference between the new centrosymmetric model in Pbcm (this work) and the previous acentric model in Pbc (Vazquez et al, 2002) In the latter case five different tetrahedral positions have to be distinguished. Al4Ca3CoO10 447.09 Orthorhombic, Pbcm 293 5.1324 (6), 16.7550 (19), 10.6822 (12) 918.60 (18) 4 Mo K 3.97 0.12 Â 0.09 Â 0.06
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