Ni and Ni–nickel oxide nanoparticles with different shapes and a core–shell structure

• Published in: Thin solid films Vol. 505; no. 1; pp. 109 - 112
• Main Authors: Nayak, Bibhuti B., Vitta, Satish, Nigam, A.K., Bahadur, D.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 18-05-2006; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Core–shell structure; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetism; Materials science; Nanoparticles; Nanopowders; Nanoscale materials and structures: fabrication and characterization; Nickel; Physics; Nanoparticles; Magnetism; Nickel; Core–shell structure; Temperature dependence; Inorganic compounds; Electrical conductivity; Magnetization; Magnetic field effects; Magnetic hysteresis; XRD; Experimental study; Chemical reduction; Particle size distribution; Transmission electron microscopy; Aqueous solutions; Transition elements; Size effect; Core-shell structure; Nanostructured materials
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2005.10.018

Ni nanoparticles with different shapes and having a core–shell structure of Ni–nickel oxide have been prepared by a combination of chemical and gaseous reduction. The first step involves chemical reduction of nickel chloride in an aqueous medium with sodium borohydride (NaBH
4). In the second step, the as prepared Ni-complex is reduced further in the presence of 2% H
2 and 98% Ar gas mixture at different temperatures ranging from 550 °C to 850 °C. For gaseous reduction temperatures up to 750 °C, structural studies done at room temperature indicate a core–shell structure of Ni–Ni-oxide whereas for reduction at 850 °C, essentially a single phase of Ni is seen. The particle size ranges from 20 to 120 nm with different shapes for the particles: spherical, ellipsoidal, cylindrical, hexagonal, and polyhedral. The electrical resistivity in all the cases exhibits a typical metallic behavior and the absolute resistivity decreases with increasing gaseous reduction temperature, indicating a progressive reduction of Ni-oxide. The magnetization studied as a function of temperature and field shows a clear core–shell behavior: very high magnetization saturation fields and thermal hysteresis of magnetization.