| One dimensional (1D) materials have attracted wide attention from condensedmatter physicists, chemists, and material scientists etc, and becoming one of the hottesttopic in nano-materials field. Atomic (molecular) chains can be taken as onedimensional nano-scale materials and is very promising in the application ofnano-connection and the functional group element in the nano-electronics, opticaldevices, which is also an ideal model to study the relation between the mechanicalparameters and size/dimensions in nanomaterials. Based on the idea that the atomicchain confined in a1D space usually has been found to be stable even at ambientconditions, to study such1D system has become practicable.1D atomic (molecular)chains can be obtained by doping the nanotubes with the typical diatomic molecules,that provides the experiment basis and theoretical support for the study of1D atomic(molecular) chains. Iodine atomic chains have been found to be stable inside theSWNT. The iodine molecular wires and a spot of iodine atomic chains can beincorprated in the channels of type5Molecular Sieve (AFI). Polarized resonantRaman scattering reveal that the iodine molecular wires and a spot of iodine atomicchains can only aligned to the channel direction while the molecular iodine orientatedrandomly. From previous studies, we found that type5Molecular Sieve (AFI) can betaken as a ideal confinement material, exhibiting the advantages of having long andstraight channels, uniform pore size and fewer defects. On the other hand, bromine, atypical diatomic molecule, similar to iodine, has rich structures transition in the lowpressure range, which makes it to be a ideal model to realize (simulate) other similardiatomic molecules, and give us additional indications in the study of pressure-inducedmetallization of hydrogen, etc.It is still an open question that the synthesis、optical characterizations and highpressure study of bromine chains in confined environment. High Pressure techniqueand Polarized resonant Raman scattering provide a new perspective to study thestructures and physical properties of1D atomic (molecular) chains.In this work, we present that bromine atomic chains have been successfullysynthesized by introducing bromine molecules into the channels of AFI (AFI) singlecrystals through a vapor phase method. The bromine absorbed on the AFI surface canbe easily removed by sublimation naturally when heated to590C for2hours and thenstored at room temperature for3days. The doped bromine@AFI samples showsgolden color, obviously different from the white color of pristine AFI crystal. The Raman spectra of bromine doped samples obviously differ from those of pristine bromine single crystals, that reveal the bromine chains(Br5-chains/(Br2)n chains and asymmetric Br3-chains) and bromine molecules formed inside the AFI channels. We assign208cm-1peak to asymmetric Br3-chains, that is also observed in Cs+Br3-. Due to size confinement of the AFL channels, the Raman peak shifts from320cm-1for gaseous Br2to314cm-1. So314m"1peak originates from isolated bromine molecules. For the peak at265cm-1, we assign it to (Br2)n or Br5-chains, that is supported by the same Raman peak at (trimesic acid.H20)10H+Br5-and our deduction has been made on the basis iodine doped into the channels of AFI. The bromine chains and bromine molecules can be stable inside the channels. Our detailed Raman study along the bromine doped AFI rods shows that the distribution of bromine in the zeolite pores is not homogeneous, with more existing in the open end of the zeolite, less in the middle.Studies of polarized Raman spectra show that the (Br2)n、symmetric Br3-and asymmetric Br3-chains are not exactly aligned the channel direction but with a slightly titled angle, while the bromine molecules are oriented randomly inside the channels of AFI.To further explore the high-pressure behavior of polybromide confined into the AFI channels, we measure an in-situ high-pressure Raman and XRD study for AFI doped with bromine. All the pressure evolution differs from the case of pristine bromine, as an additional proof of the intercalation process. We firstly assume that the265cm-1can be attributed Br5-wires. At0.16-3.74GPa, bromine molecules interact with the asymmetric Br3-chains and Br5-chains can be synthesized. Br2+Br3-'Br5-， increasing the amount of the Br5-chains. If this happened, the below scheme will happen:Br2+Br5-'Br7-,but we can’t observe the large frequency shift at Br5-peak or new raman peaks appear and become more intensity at pressure. So we suggest that the265cn-1more reasonably originate from (Br2)n wires rather than Br5-wires, that is similar to (I2)n wires formed inside the channels of AFI crystal. At0.2-3.7GPa, pressure can mBr2+(Br2)n'(Br2)m+n or mBr2+nBr2'(Br2)m+n, prolongating or increasing the amount of the (Br2)n wires. A slope change has been observed in all the curves at-7GPa. In detail, at this pressure the peak starting from305cm-1due to bromine chain increases abruptly in its frequency. After the highest pressure (18GPa)reached in this study the framework is completely destructed and becomes irreversibleupon decompression. All these results are further confirmed by Raman measurementson the samples decompressed from different high pressures.The structural stability of Br@AFI zeolite (AFI) has been studied as a function ofpressure up to18.8GPa in a diamond anvil cell by using synchrotron X-ray diffraction.It is found that the AFI structural stability can be enhanced significantly when brominespecies doped into the AFI channels. In this case the (400) and (410) peaks are stillexist at18.8GPa, while the AFI crystals become amorphous state at higher pressure.The bromine chains and bromine molecules in channels of AFI affect the structuralevolution of the AFI channel under pressure. The results demonstrated that brominecan be doped into the channels of porous zeolite AFI single crystals, exerting asupporting effect against the structure collapse of AFI and thus improving theirstructural stability. |
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