The Study Of The Polymorazation Of Boron Nitride Nanotube Bundlles Under High Pressure

In current study, we construct noevl BN phase by replacing the atoms of carbonphase to B and N, and then study properties and stability of these BN allotrops by MaterialStudio software. The results show they stable at0GPa with unique properties.We do a computational simulation about phase transition of single-wall (SW) boronnitride nanotubes (BNNTs) under high pressure, by CASTEP program in MS. The resultsshow, under high pressure, the BNNTs would interlink together, and we can obtain somethree dimensional (3D) BNNT polymers. Under high pressure, the BNNTs would haveelastic deformation, and then as the pressure increased, the interlinking occurs. There aretwo ways to conjunction together between the adjacent nanotubes, one is connect togetherdirectly with small deformation of nanotubes, the other one is connect together with bigdeformation of tubes, in this situation, the tubes will be collapsed. These3D BNNTpolymers has special structural features and with unique properties.The properties studies of these3D BNNT polymers shows, all of them aremechanical stable, and one of them bulk modules is close to cubic BN (c-BN). Thecalculated Vikers hardness shows, three of them are superhard materials, the tensilestrength calculate show the axial tensile strength is higher than the raw tubes, theelectronic properties show that all of them are wide band gap semiconductor. The phonondispersion shows all of these polymers are dynamical stable.We studies the high pressure high temperature (HPHT) phase transition of multi-wall(MW)BNNT experimentally. The results show, under HPHT conditions, the MWBNNTwould transform into some other phase, this phase transition is dependent to the pressureand temperature. Under25GPa conditions, at room temperature, may be the phasetransition is reversely or there are no phase transition, at500℃, the phase transitionproducts are BNNT and wurtize like BN (w-BN), at1000℃, the phase transition productsare wurtize like BN (w-BN) abd cubic BN, which main phase is w-BN, at1500℃,thetransition product are wurtize like BN (w-BN) abd cubic BN, which main phase is c-BN.