Investigations on the crystal-structure and non-ambient behaviour of K2Ca2Si8O19 - a new potassium calcium silicate
Abstract
Within the context of a systematic re-investigation of phase relationships between compounds of the ternary system K2O-CaO-SiO2 a new potassium calcium silicate with the chemical formula K2Ca2Si8O19 was synthesized via solid state reactions as well as the flux method using KCl as a solvent. Its crystal structure was determined from single-crystal X-ray diffraction data by applying direct methods. The new compound crystallizes in the triclinic space group P 1 bar . Unit cell dimensions are a = 7.4231(7) Å, b = 10.7649(10) Å, c = 12.1252(10) Å, α = 70.193(8)°, β = 83.914(7)° and γ = 88.683(7)°. K2Ca2Si8O19 is built up of corner-connected, slightly distorted [SiO4]-tetrahedra forming double-sheets, which are linked by double-chains of edge-sharing [CaO6]-octahedra. Electroneutrality of the material is provided by additional potassium atoms that are located within the voids of the silicate layers and between adjacent [Ca2O6]-double-chains. Further characterization of the compound was performed by Raman spectroscopy and differential thermal analysis. The behaviour of K2Ca2Si8O19 under high-temperature and high-pressure was investigated by in-situ high-temperature powder X-ray diffraction up to a maximum temperature of 1125 °C and a piston cylinder experiment at 1.5 GPa and 1100 °C. Additionally an overview of known double-layer silicates is given as well as a comparison of K2Ca2Si8O19 to closely related structures.
- Publication:
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Journal of Solid State Chemistry France
- Pub Date:
- September 2017
- DOI:
- 10.1016/j.jssc.2017.06.011
- Bibcode:
- 2017JSSCh.253..336S
- Keywords:
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- K<SUB>2</SUB>Ca<SUB>2</SUB>Si<SUB>8</SUB>O<SUB>19</SUB>;
- Single-crystal X-ray diffraction;
- Powder X-ray diffraction;
- Double-layer silicate;
- Ternary system K<SUB>2</SUB>O-CaO-SiO<SUB>2</SUB>;
- Phase relationships