Upon cooling from its hexagonal high-temperature modification, AlPO4 (aluminium phosphate) tridymite successively transforms to several displacively distorted forms, including a normal structure-incommensurate-lock-in phase transition sequence. The space-group symmetries in this series are P112(1), P112(1)(alphabeta0) and P2(1)2(1)2(1), respectively. The distortion pattern of the intermediate P112(1) phase can be described as alternate shifts of adjacent layers of tetrahedra coupled with tilting of the tetrahedra. The symmetry and direction of the shifts are different from the analogous SiO2 tridymite modification. The atomic displacement parameters of the O atoms are strongly anisotropic due to thermal motions of the rigid tetrahedra. Condensation of a lattice vibration mode results in the formation of an incommensurate structural modulation below 473 K. The 3+1 superspace-group symmetry of the modulated phase is P112(1)(alphabeta0).
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Microporous aluminophosphates synthesized with 1,2,3-trimethylimidazolium and fluoride.
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Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Sor Juana Inés de la Cruz 3, 28039 Madrid, Spain.
The synthesis of microporous aluminophosphates using 1,2,3-trimethylimidazolium (123TMI) and fluoride produces three phases (HPM-3, PST-27 and triclinic AlPO4-34) depending on the amount of water and organic structure-directing agents in the synthesis mixture. Fluoride occluded in double 4-ring units was not detected by (19)F MAS NMR spectroscopy in any product. While the structure of HPM-3 remains unknown, PST-27 has been determined to be a monoclinic version of AlPO4-5 with a distorted and likely complex structure.
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Institute for Study of the Earth's Interior, Okayama University, 827 Yamada, Misasa, Tottori 682-0193, Japan.
Structural characterization of a new high-pressure AlPO(4) phase synthesized at 5 GPa and 1500 °C is reported. The phase is monoclinic (P2/a) with a = 8.7437(1) Å, b = 4.
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Institute for Study of the Earth's Interior, Okayama University, 827 Yamada, Misasa, Tottori 682-0193, Japan.
The crystal structures of two new high-pressure AlPO(4) phases are reported. One phase synthesized at 6 GPa and 1523 K is triclinic (P1) whilst the other phase synthesized at 7 GPa and 1773 K is monoclinic (P2(1)/c). (31)P MAS (magic-angle spinning) NMR suggests three tetrahedral P sites with equal abundance in both phases.
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Acta Crystallogr C
January 2002
Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Upon cooling from its hexagonal high-temperature modification, AlPO4 (aluminium phosphate) tridymite successively transforms to several displacively distorted forms, including a normal structure-incommensurate-lock-in phase transition sequence. The space-group symmetries in this series are P112(1), P112(1)(alphabeta0) and P2(1)2(1)2(1), respectively. The distortion pattern of the intermediate P112(1) phase can be described as alternate shifts of adjacent layers of tetrahedra coupled with tilting of the tetrahedra.
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