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S. Rakic, Volker Kahlenberg, B. C. Schmidt, S. Ide
High pressure mixed alkali disilicates in the system Na2— xKxSi2O5: hydrothermal synthesis and crystal structures of NaKSi2O5-II and Na0.67K1.33Si2OThe subsequent refinement converged to a residual of R(ΙFΙ) = 0.037 for 1543 independent reflections. The compound is mono clinic as well with space group I2/a (a = 12.731(2) Å, b = 7.321(1) Å, c = 17.827(3) Å, β = 100.85(2)° V = 1631.9(6) Å3, Mr = 206.32 u, Z = 12, Dx = 2.53 g/cm3, μ(MoKα) = 1.78 mm–1) and belongs to the group of single layer silicates. A single layer consists of four-, six- and eight-membered rings, which are parallel to (100), and can be described as being built by the condensation of unbranched dreier single chains running along the b-axis. The stacking of the layers results in a three-dimensional structure in which the alkali cations reside between the layers for charge compensation. The distribution of the alkali atoms among the three crystallographically different positions M(1), M(2) and M(3) shows a definite preference of the larger potassium for the M(1) and M(2) site; the M(3) site is K-free. The alkali-atoms are 5- and 6- fold coordinated by the oxygen atoms. The geometrical and topological features of the single tetrahedral sheets in Na0.67K1.33Si2O5 are very similar to those observed in the phase I of NaKSi2O5. Differences can be attributed to different ways of stacking of adjacent sheets, and different sequences of up and down pointing tetrahedra within the rings.
Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0044-2968
Volume: 218, 06/2003
Pages: 413
The subsequent refinement converged to a residual of R(ΙFΙ) = 0.037 for 1543 independent reflections. The compound is mono clinic as well with space group I2/a (a = 12.731(2) Å, b = 7.321(1) Å, c = 17.827(3) Å, β = 100.85(2)° V = 1631.9(6) Å3, Mr = 206.32 u, Z = 12, Dx = 2.53 g/cm3, μ(MoKα) = 1.78 mm–1) and belongs to the group of single layer silicates. A single layer consists of four-, six- and eight-membered rings, which are parallel to (100), and can be described as being built by the condensation of unbranched dreier single chains running along the b-axis. The stacking of the layers results in a three-dimensional structure in which the alkali cations reside between the layers for charge compensation. The distribution of the alkali atoms among the three crystallographically different positions M(1), M(2) and M(3) shows a definite preference of the larger potassium for the M(1) and M(2) site; the M(3) site is K-free. The alkali-atoms are 5- and 6- fold coordinated by the oxygen atoms. The geometrical and topological features of the single tetrahedral sheets in Na0.67K1.33Si2O5 are very similar to those observed in the phase I of NaKSi2O5. Differences can be attributed to different ways of stacking of adjacent sheets, and different sequences of up and down pointing tetrahedra within the rings.
Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0044-2968
Volume: 218, 06/2003
Pages: 413