Variation of crystal structure in nickel nanoparticles filled in carbon nanotubes

Carbon nanotubes (CNTs) filled with metals can be used in capacitors, sensors, rechargeable batteries and so on. Atomic arrangement of the metals plays an important role in the function of the composites. Here, we show that Ni and NiO nanoparticles in CNTs are crystalline, which results in the occurrence of lattice shrinkage. Interplanar spacing of (111)(Ni), (200)(Ni), (220)(Ni) and (311)(Ni) lattice plane decreases by 0.08-0.35%. The crystal lattice constant of the Ni diminishes by 0.35%. Lattice shrinkage causes a misfit of the lattice constant between the nickel and the internal CNT surface: from theoretical 1.21% to actual 0.86%. This variation is beneficial to heterogeneous nucleation of Ni crystal nucleus on the surface at a point with the lowest interfacial energy at coherent interface, where the match is (111)(Ni)//(0001)(C). According to our findings, one-dimensional nanostructures can be changed and controlled during synthesis by use of CNTs as a template.