High Pressure Studies On The BN Nanotubes And C₆₀@BN Nanotube Peapods

As a typical representative of one dimensional nanomaterials,the one dimensional nano channe of boron nitride nanotube?BNNT?provides an excellent template for the study of confinement meterials,and make the encapsulated materials exhibit peculiar structures and properties.High pressure can change the molecular distance and affects the structure properties.High pressure studies on confinement meterials not only can help us discover their various properties deeply,but also provide new insights for buliding novel structures.We investigated the difference between the BNNT and C₆₀@BNNT by in-situ high pressure Raman spectroscopy,Infrared spectroscopy,and thus their phase transitions under high pressure.We also studied the pressure evolution of C₆₀ in the boron nitride nanotubes and the condition of polymerization in this new structure by Raman spectroscopy.The results can be summarized below:1.In-situ Raman spectroscopy and Infrared Spectroscopy studies under high pressure were carried out on BNNTS up to 36GPa,which exhibit the hexagonal-to-wurtzite structural transformation with the formation of sp³ bonding at around 19GPa in BNNTs.However,as for the C₆₀@BNNT,the transformation started at around 13GPa.Because of the existence of C₆₀0 molecules,the nanotubes were influenced by the external and internal pressure during compression,which decrease the pressure of the phase transition.Above 20GPa,the sp³ bands between the tube walls became saturated,and the sp³ bonds inside the tubes began to form while the transition was still incompleted even up to 36GPa.After decompression,the transition from wurtzite to a hexagonal structure was partially reversible for BNNTs but irreversible for C₆₀@BNNTs.2.In-situ High pressure X-ray diffraction was carried out on BNNTs up to 90GPa with liquid argon as pressure medium.BNNTs has a hexagonal structure with a dominant?002?peak at ambient pressure,and transform into wurtzite structure with the appearance of?100?and?002?peaks at 19GPa.During the whole compression and decompression process,boron nitride nanotubes contain hexagonal and wurtzite structures.We can conclude that the unique nanotube structure of BN makes the transformation into wurtzite structured BN irreversible and the w-BN is quenchable to ambient conditions.3.The polymerization of C₆₀0 molecule in C₆₀@BNNT has been studied up to40GPa by in-situ Raman spectroscopy with liquid argon as pressure medium.We found the Raman peaks of C₆₀0 still exist,indicating no polymerization was formed,while after decompression from 20Gpa and 30GPa,we found C₆₀s form 1D linear polymerized o-phase.it meant boron nitride nanotube provides a confinement environment for the polymerization of C₆₀ molecules and makes the transition irreversible.