The glass-like structure of iron–nickel nanochains produced by the magnetic-field-induced reduction reaction with sodium borohydride

Abstract

Preparation and detailed structural characterization of iron–nickel wire-like nanochains with Fe_0.75Ni_0.25, Fe_0.50Ni_0.50, and Fe_0.25Ni_0.75 compositions are reported. The investigated nanomaterials were produced by the novel template-free magnetic-field-induced reduction reaction with NaBH₄ as the reducing agent. It is demonstrated that this method leads to the formation of Fe–Ni nanochains composed of spherical nanoparticles with an average diameter of 50–70 nm and with a very high degree of atomic disorder manifested as the lack of clearly developed bcc and fcc phases, which are usually observed for nano- and polycrystalline Fe–Ni species. The recorded wide-angle X-ray scattering data for the obtained Fe–Ni nanochains exhibit a strong resemblance to those obtained for bulk metallic glasses. The atomic scale structure of the investigated nanochains has been studied using pair distribution function analysis of the recorded total scattering data. The best fits to the experimental pair distribution functions have been achieved assuming two-phase models of hcp and bcc networks with the size of coherently scattering regions of about 2.5 nm in diameter, for each Fe–Ni composition. The transmission electron microscopy images indicate that the glass-like bimetallic alloy cores are covered by amorphous oxide/hydroxide shells with their thickness ranging from 2 to 5 nm. Moreover, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy results confirm the core–shell structure of the Fe–Ni nanochains and the complex character of the shell layer which consists of several iron- and nickel-containing phases.