What is it about?
The modulated structures of (Sr0.13Ca0.87)2CoSi207 at 293K and Ca2CoSi207 at 293, 393, 468 K are compared to find the peculiarity of the partial substitution of Ca by larger alkaline-earth atoms such as Sr. The similarities in structural effects of this substitution and heating are found.
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Why is it important?
(Sr0.13Ca0.87)2CoSi207 and Ca2CoSi207belong to the family of melilite-type compounds A2T(1)T(2)207and are characterized by twodimensional incommensurate structures at ambient temperatures. For melilites it was supposed that a misfit between the sizes of interlayer cations A and the large space for A formed by the tetrahedral sheets might be responsible for the modulation'. In the present paper the structuresof the Ca2CoSi207crystal at 293, 393, 468 K and (Sr0.13Ca0.87)2CoSi207 at 293 K have been compared to find effects of the substitution of the interlayer cations.
Perspectives
Comparison of the Co-Akermanite structures clarified that the partial substitution of the Ca by larger Sr decreases the distortion of the polyhedra around the cations and makes the structure more similar to the high temperature variant. Thus, the process of increasing the size of the atom at the A-site by partial substitution forces the structure closer to the normal state, in the same way asraising the temperature in pure Co-Akermanite increases the apparent size of the atoms. The study proves that the characteristics of the modulation in Akermanites are correlated with the misfit of sizes of the A-site interstices and the apparent sizes of the interlayer cations, and these are controlled by isomorphous substitution as well as by variation of temperature.
Dr Bagautdin Bagautdinov
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This page is a summary of: Two-dimensional incommensurate structures of (Sr0.13Ca0.87)2CoSi2O7and Ca2CoSi2O7: Effects of substitution of interlayer cations, Ferroelectrics, February 2001, Taylor & Francis,
DOI: 10.1080/00150190108225032.
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