Structural and dynamics properties of methane confined phase in AlPO4-5 model aluminophosphate: An illustrative example of quasi-(1D) phase transition

We present a detailed study of both structural and dynamics properties of methane confined phase in AlPO4-5 model alumino-phosphate, performed by neutron diffraction (CD4) and quasi-elastic incoherent neutron scattering (CH4). Such a system is a unique example of quasi-(1D) phase transition between two commensurate solids. When increasing the methane loading, we observe a first solidification of the CD4 confined phase giving rise to a commensurate methane “dimers” chain and a second one at higher loading giving rise to a commensurate methane “trimers” chain. Between the two methane confined solid phase a “re-entrant” fluid phase is observed.

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► Confined methane phase on AlPO4-5 model alumino-phosphate.
► Unique example of quasi-(1D) phase transition between two solids A and B.
► Solid-A is a commensurate methane “dimers” chains.
► Solid-B is e semi-commensurate methane “trimers” chains.
► In between the two solids A and B, a “re-entrant” fluid phase is observed.