Thermal behavior and structural transformation in the chabazite-type zeolite willhendersonite, KCaAl3Si3O12×5H2O
- Author(s)
- Ekkehart Tillmanns, Christian Lengauer
- Abstract
Single crystals of the chabazite-type zeolite mineral willhendersonite, KCaAl3Si3O12×5H2O (fromBellerberg, eastern Eifel district, Germany), were studied by X-ray diffraction methods between 100and 500 K. The zeolite shows a phase transition from triclinic to rhombohedral symmetry between 350and 375 K under dry nitrogen and between 450 and 475 K under humid air. Under these conditions,the unit-cell parameters change from P1 at 350 K [a, b, c (Å); alpha, beta, gamma (°); V (Å3) = 9.210, 9.210, 9.405;92.75, 92.80, 90.80; 795.8] to R3 at 375 K (a = 9.380 Å, alpha = 91.40°, V = 824.5 Å3), and from P1 at450 K [a, b, c (Å); alpha, beta, gamma (°); V (Å3) = 9.215, 9.215, 9.415; 92.65, 92.85, 90.75; 797.5] to R3 at 475K (a = 9.375 Å, alpha = 91.35°, V = 823.8 Å3), respectively. The crystal structures were refined based onX-ray diffraction data collected at room temperature [P1; a, b, c (Å); alpha, beta, gamma (°); V (Å3) = 9.248(5),9.259(5), 9.533(5); 92.313(5), 92.761(5), 89.981(5); 814.7(8)], at 373 K [P1; a, b, c (Å); alpha, beta, gamma (°);V (Å3) = 9.205(5), 9.231(5), 9.442(5); 92.550(5), 93.086(5), 90.519(5); 800.3(8)], and at 423 K [R3, a= 9.411(4) Å, alpha = 91.48(1)°, V = 832.7(6) Å3]. Upon heating, the elliptical 8-rings of willhendersoniteexpand to a triangular shape in the rhombohedral structure with upper and lower rings in the double6-ring (D6R) twisted by 60° to each other corresponding to the center of symmetry in the center ofthe D6R. The changes in the framework are accompanied by migration of cations, partly assumingunfavorably low coordinations in the high temperature structure due to the loss of H2O molecules.Rehydration at room temperature yields the triclinic structure of willhendersonite, although the singlecrystals become polysynthetically twinned.
- Organisation(s)
- Department of Mineralogy and Crystallography
- Journal
- American Mineralogist: an international journal of earth and planetary materials
- Volume
- 93
- Pages
- 1317-1325
- No. of pages
- 9
- ISSN
- 0003-004X
- Publication date
- 2008
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 104021 Structural chemistry
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/931d0614-2253-4448-9af7-1286cf9c4575