T-induced displacive phase transition of end-member Pb-lawsonite

摘要: Pb-lawsonite, PbAl 2 [(OH) |Si O 7 ]·H O, space group Pbnm , was synthesized as crystals up to 15 µm × 5 µm × 5 µm in size by a piston cylinder technique at pressure of ∼4 GPa and temperature 873 ± 10 K. Temperature-dependent powder single-crystal X-ray diffraction (XRD) analyses partly using synchrotron radiation well Raman spectroscopic investigations reveal phase transition around 445 K resulting the Cmcm high-temperature structure. The transformation is considerably higher than that lawsonite 273 K, which characterized predominantly proton order/disorder. confirmed principal component analysis subsequent hierarchical cluster on both XRD patterns spectra. Furthermore, non-uniform change observed 355 K, not pronounced apparently comes from enhanced hydrogen bonding, stops atom shifts Pb-lawsonite. These are same bonds mainly characterize 273 K. In contrast, structural Pb-lawsonite seems originate interaction SiO 4 tetrahedra AlO 6 octahedra framework with Pb 2+ cation. environment can be described 12-fold coordination above 445 K, changes towards irregular ten-fold below this temperature. An assignment O–H stretching bands confirms moderately strong H whereas weak exist lawsonite. Therefore, further similar expected.