The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 A ˚ and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by [2+4]Hg polyhedra and (As3+2S5)4-groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.
Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula / Arianna Lanza, Mauro Gemmi, Luca Bindi, Enrico Mugnaioli, Werner H. Paar. - In: ACTA CRYSTALLOGRAPHICA. SECTION B. - ISSN 1600-5740. - STAMPA. - 75:(2019), pp. 711-716.
Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula
Luca Bindi;
2019
Abstract
The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 A ˚ and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by [2+4]Hg polyhedra and (As3+2S5)4-groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.File | Dimensione | Formato | |
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