Résumé
The structure of a high-pressure polymorph of glycine (the Β′ -polymorph formed reversibly at 0.8 GPa from the Β -polymorph) was determined from high-resolution X-ray powder diffraction data collected in situ in a diamond anvil cell at nine pressure points up to 2.6 GPa. X-ray powder diffraction study gave a structural model of at least the same quality as that obtained from a single-crystal diffraction experiment. The difference between the powder-diffraction and the single-crystal models is related to the orientation of the N H3 -tails and the structure of the hydrogen-bonds network. The phase transition between the Β - and Β′ -polymorphs is reversible and preserves a single crystal intact. No transformations were observed between the Β -, α -, and Β′ -polymorphs on compression and decompression, although the α - and Β′ -polymorphs belong to the same space group (P21/c). The instability of the Β - and γ -forms with pressure can be predicted easily when considering the densities of their structures versus pressure. The direction of the transformation (i.e., which of the high-pressure polymorphs is formed) is determined by structural filiation between the parent and the high-pressure phases because of the kinetic control of the transformations.
langue originale | Anglais |
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Pages (de - à) | 307-316 |
Nombre de pages | 10 |
journal | Powder Diffraction |
Volume | 23 |
Numéro de publication | 4 |
Les DOIs | |
Etat de la publication | Publié - 2008 |
Modification externe | Oui |
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