English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The formation of polycrystalline Na 2 Ca 4 Mg 2 Si 4 O 15  from solid state reactions has been studied between 800 and 1050°C. Single crystals of the compound have been grown in a closed platinum capsule by slow cooling in the temperature range between 1300 and 1000°C. Basic crystallographic data are as follows: monoclinic symmetry, space group  P 12/ c 1,  a =7.1717(3) Å,  b =5.3512(2) Å,  c =16.4789(7) Å, β=90.911(4)°, V=632.33(4) Å 3 , Z=2. A conspicuous feature of the crystals is an intensive lamellar non-merohedral twinning clearly observable already under a petrographic microscope. The diffraction pattern can be explained as a superposition of two reciprocal lattices with a two-fold axis parallel to [001] being the twin element. Using synchrotron radiation it was possible to solve the crystal structure of Na 2 Ca 4 Mg 2 Si 4 O 15  from a twinned data set. Least-squares refinements resulted in a residual of R(|F|)=0.031 for 2899 observed reflections with I&gt;2σ(I) and 127 parameters. The crystal structure contains both [Si 2 O 7 ]-dimers and insular [SiO 4 ]-moieties. Tetrahedra and [MgO 6 ]-octahedra form a three-dimensional framework whose topological characteristics have been studied. The remaining calcium and sodium cations are distributed among four crystallographically independent positions located in voids of the network. On a microscopic scale the twinning observed in the diffraction experiments could be explained by the existence of a 2 1 -screw axis parallel to [001] in (¼, 0,  z ) mapping both domains onto each other. A comparison with related compounds having an A +  2 B 2+  6 Si 4 O 15  stoichiometry is presented. More than 25 years after its first observation in refractories our investigation clarifies the crystal structure of a silicate that is of relevance for both Materials science and high pressure research.

Synthesis, synchrotron diffraction study and twinning in Na 2 Ca 4 Mg 2 Si 4 O 15 – a heteropolyhedral framework compound