Novel properties of boron nitride nanotubes encapsulated with Fe, Co, and Ni nanoclusters.

Using state of the art spin polarized density functional theory, we report the stability and structural aspects of small magnetic clusters M(4) (M = Fe, Co, and Ni) inside an inert boron nitride nanotube [BNNT(10,0)]. The geometry optimization was carried out starting with various possible configurations [one-dimensional (1D) linear chain, two-dimensional (2D) planar rhombus, and three-dimensional (3D) tetrahedral], and the results reveal that the ground state geometry of M(4) cluster inside the nanotube favors 3D configuration over others. Moreover, these small clusters are found to retain their magnetic nature with a small reduction in the total magnetic moment even after encapsulation. The radial confinement effect on the atomic structure of M(4) clusters was investigated by optimizing the Co(4) (prototype example) in BNNT(10, 0), BNNT(9, 0), and BNNT(8, 0). It is found that with the increase in radial confinement (smaller diameter), the Co(4) cluster becomes more compact, which further leads to significant changes in the electronic and magnetic properties. The electronic density of states analysis of the M(4) clusters inside BNNT(10,0) showed the appearance of additional electronic states in the band gap of BNNT(10, 0). In order to underscore the possibility of functionalizing these encapsulated tubes, we have performed the adsorption of oxygen molecules on it. The adsorption of oxygen in the molecular form with elongated O-O bonds further justifies its application in the oxidative catalysis.