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The ambient-temperature compressibility and room-pressure thermal expansion of two Mg3(PO4)2 polymorphs (farringtonite = Mg3(PO4)2-I, with 5- and 6-fold coordinated Mg, and chopinite = “Mg-sarcopside” = [6]Mg3(PO4)2-II), three Mg2PO4OH polymorphs (althausite, hydroxylwagnerite and ε-Mg2PO4OH, all with [5]Mg and [6]Mg) and phosphoellenbergerite ([6]...
Contexts in source publication
Context 1
... such a narrow and structurally peculiar basis, it proved hazardous to assume average compressibility and thermal-expansion values for magnesium phosphates -or for given structural groups of phosphates, as tentatively done for silicates by Holland and Powell (1985) in their early thermodynamic database. Indeed, although they all are orthophosphates, the relevant Mg-phosphates show a variety of structural types (Table 1): from the relatively open structures of farringtonite and ε-Mg 2 PO 4 OH with 5-and 6-fold coordinated Mg and packing efficiencies near 19-20 Å 3 per oxygen to more densely packed phases (near 18 Å 3 per oxygen) like althausite and hydroxylwagnerite with again 5-and 6-fold coordinated Mg to compact structures (≤ 18 Å 3 per oxygen) like chopinite with Mg in edge-sharing octahedra and phosphoellenbergerite with Mg in face-sharing octahedra. ...Context 2
... literature data were used as input values for cell parameters (Table 1) and atomic positions; the latter were kept constant throughout the refinement procedure. The refined data set included the cell parameters, the overall scale factor, a profile shape factor, coefficients of the FWHM (full width at half maximum) Caglioti's polynomial and background parameters. ...Context 3
... tensor elements α ii × 10 5 (K −1 ) β ii × 10 3 (GPa −1 ) Note: data for forsterite and Si-ellenbergerite were recalculated from the cited literature. In the case of Kroll et al. (2012), data from their Table 1 were used with the exception of the results below 20 °C. Forsterite was in the Pnam setting for consistency with that of chopinite (Table 6). ...Context 4
... 7. Projection of the chopinite structure along b axis (adapted from Grew et al., 2007). The a and c axes are according to our setting in Table 1. Representation quadric of the tensors of compression (blue) and thermal expansion (green) according to Nye (1985) and Knight (2010 10 (β c /β a = 1.33) and can be related to the properties of the two main structural elements, the octahedral single and double chains running parallel to c. ...Similar publications
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Citations
We used synchrotron XRD measurements and density-functional theory calculations to unravel the high-pressure properties of Co 3 P 2 O 8 . Co 3 P 2 O 8 undergoes a phase transition at 2.9 GPa to an olivine-type structure.
