XRD and pair distribution function to determine anisotropic atomic displacement parameters of tridymite and cristobalite

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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XRD and pair distribution function to determine anisotropic atomic displacement parameters of tridymite and cristobalite

Messaggio da Marco E. Ciriotti » sab 16 mar, 2019 12:16

Referenza:
▪ Lee, S. & Xu, H. (2019): Using powder XRD and pair distribution function to determine anisotropic atomic displacement parameters of orthorhombic tridymite and tetragonal cristobalite. Acta Crystallographica, B75, 160-167.

Abstract:
Determination of the crystal structures of low‐temperature tridymite and cristobalite using single‐crystal XRD has been challenging because they generally occur as metastable fine‐grained crystals in the geological environment. Therefore, using powder diffraction and scattering techniques is critical to study the low‐temperature crystals. Synchrotron powder X‐ray diffraction (XRD), pair distribution function (PDF) and transmission electron microscopy were used to investigate the structure of orthorhombic tridymite with C2221 symmetry and tetragonal cristobalite with P41212 symmetry, including their anisotropic atomic displacement parameters (ADPs). Rietveld refinement was used to determine the unit‐cell parameters, fractional coordinates and isotropic atomic displacement parameters (Uiso) of the tridymite and cristobalite. The PDF method was used to determine ADPs for each atom. The results suggest that the crystal structure with high quality ADP values can be obtained using the combined methods of XRD and PDF analyses. The method can be used for characterizing crystals that are not suitable for single‐crystal XRD.


_chemical_name_mineral Tridymite

# Unit cell
_cell_length_a 8.7549(5)
_cell_length_b 5.0335(3)
_cell_length_c 8.2118(4)
_cell_angle_alpha 90
_cell_angle_beta 90
_cell_angle_gamma 90
_symmetry_cell_setting orthorhombic
_space_group_name_H-M_alt 'C 2 2 21'


chemical_name_mineral Cristobalite

# Unit cell
_cell_length_a 4.9727(6)
_cell_length_b 4.9727(6)
_cell_length_c 6.9257(5)
_cell_angle_alpha 90
_cell_angle_beta 90
_cell_angle_gamma 90
_symmetry_cell_setting tetragonal
_space_group_name_H-M_alt 'P 41 21 2'
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

Avatar utente
Marco E. Ciriotti
Messaggi: 25417
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: XRD and pair distribution function to determine anisotropic atomic displacement parameters of tridymite and cristoba

Messaggio da Marco E. Ciriotti » mer 10 apr, 2019 15:32

Testo aggiornato.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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