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dc.contributor.authorGatta, G. Diego
dc.contributor.authorRotiroti, Nicola
dc.contributor.authorZanazzi, Pier Francesco
dc.contributor.authorRieder, Milan
dc.contributor.authorDrábek, Milan
dc.identifier.citationAmerican Mineralogist. 2008, vol. 93, no. 7, p. 988-995.en
dc.description.abstractCrystalline CsAlSiO4 was synthesized from a stoichiometric mixture of Al2O3 + SiO2 + Cs2O (plus excess water) in Ag-capsules at hydrostatic pressure of 0.1 GPa and temperature of 695 °C. The duration of synthesis was 46 h. The crystal structure of CsAlSiO4 was investigated by single-crystal X-ray diffraction. The structure is orthorhombic with Pc21n space group and lattice parameters: a = 9.414(1), b = 5.435(1), and c = 8.875(1) Å. Because of the orthohexagonal relation between b and a (a b3), within the standard uncertainty on the lattice parameters, a hexagonal superlattice exists, which is responsible for twinning. The crystals are twinned by reflection, with twin planes (110) and (310): twinning in both cases is by reticular merohedry with twin index 2 and hexagonal twin lattice (LT). The transformation from the lattice of the individual (Lind) to LT is given by: aT = aind – bind, bT = 2bind, and cT = cind. The refinement was initiated using the previously published atomic coordinates for RbAlSiO4. The final least-square cycles were conducted with anisotropic displacement parameters. R1 = 3.04% for 66 parameters and 2531 unique reflections. For a more reliable crystallographic comparison the crystal structure of RbAlSiO4 is reinvestigated here adopting the same data collection and least-squares refinement strategy as for CsAlSiO4. The crystal structure of the CsAlSiO4 feldspathoid is built on an ABW framework type, showing a fully ordered Si/Al-distribution in the tetrahedral framework. The only extra-framework site is occupied by Cs, lying off-center in the 8mR-channels. CsAlSiO4 is more likely to retain Cs when immersed in a fluid phase, relative to several other Cs-bearing zeolites. The topological configuration of the Cs-polyhedron (and its bonding environment), the small dimension of the pores and the high flexibility of the ABW framework type would imply a better thermal and elastic stability of CsAlSiO4 than those of the zeolitic Cs-aluminosilicates. In this light, CsAlSiO4 can be considered as a functional material potentially usable for fixation and deposition of radioactive isotopes of Cs and can also be considered as a potential solid host for a 137Cs -radiation source to be used in sterilization applications.en
dc.publisherMineralogical Society of Americaen
dc.relation.ispartofseriesAmerican Mineralogisten
dc.subjectABW framework typeen
dc.subjectcrystal structureen
dc.subjectnuclear waste disposal phaseen
dc.titleSynthesis and crystal structure of the feldspathoid CsAlSiO4 : an open-framework silicate and potential nuclear waste disposal phaseen
dc.identifier.locationNení ve fondu ÚKen

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