Russian Mineralogical Society
Fedorov session 2016
Thermal behaviour of nefedovite, Na5Ca4(PO4)4F

RMS-DPI code:  2016-1-1-0
Scientific session:  1. Mineralogical crystallography, crystal chemistry and new minerals
Author listing:  Avdontseva M.S., Krzhizhanovskaya M.G., Krivovichev S.V., Yakovenchuk V.N.
Principal author:  Avdontceva Margarita Sergeevna
Language:  Russian
Abstract - Summary 
(short description):
Nefedovite, Na5Ca4(PO4)4F is a rare sodium and calcium fluorophosphate. The crystal structure of nefedovite could be described as antiperovskite - type. It is based upon anion-centered [FCa4Na2]9+ octahedra, which link through Na1 cations in chains located along the direction [001]. (PO4)3- tetrahedra and Na2 cations are located in cavities between the chains. Nefedovite is tetragonal, I-4, a = 11.6582(2), c = 5.4111(1) Å, V = 735.45(5) Å3, Z = 2. Thermal behavior of mineral was studied by high-temperature X-ray powder diffraction method (30 - 600 º C) and by single crystal X-Ray diffraction analysis at -173 ºC, room temperature and at 150 ºC. The analysis of the data showed that the thermal expansion has anisotropic character and the anisotropy increases with temperature. The structure expands more intensively in the direction perpendicular to anion-centered chains. Thus the anion-centered chains are the strongest structural units in the structure of nefedovite and practically unchanged with temperature increasing whereas the PO4 tetrahedra rotate around the diagonal [-110] of the base of the tetragonal cell. This fact could be an explanation of this kind of thermal expansion.
Date of presentation:  10/10/2016
Presentation Place:  Mining University, foyer of the Assembly Hall
RMS-DPI code:  2016-1-1-0
File of proceedings 
 121 K
Status:  preprint
Accepted:  28/08/2016
Contact author(s):  Avdontseva, Margarita Sergeevna

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