Correlation between electron state density change and the electrical resistivity and magnetic permeability changes in the nanostructured powder of the NiMo alloy

Abstract

The nanostructured powders of the Ni 95.4Mo 4.6 and Ni 99Mo 1 alloys (average crystallite dimensions of 14 and 21 nm) were obtained by the electrochemical deposition from ammonium solutions of nickel and molybdenum salts. The method of differential scanning calorimetry (DSC) and measurement of temperature dependence of the powder's electrical resistivity, magnetic permeability and the thermoelectromotive force were employed to examine structural changes of the powders. The nanocrystalline alloys Ni 95.4Mo 4.6 and Ni 99Mo 1 were stable up to about 460 K. The thermal stabilization of the alloys takes place within the temperature interval of 460–570 K. As a result of this process, a decrease in the electrical resistivity and increases in magnetic permeability as well as electron state density in the proximity of the Fermi level are observed. The crystallization temperature depends upon the current density of powder formation. The nanocrystalline alloy Ni 95.4Mo 4.6 obtained at j=70 mA cm −2 becomes crystallized in the temperature range between 650 and 840 K, while the Ni 99Mo 1 alloy obtained at j=180 mA cm −2 crystallizes in the 580–950 K temperature interval. The electrical resistivity and magnetic permeability of the nanocrystalline alloy decreased while the alloy's electron state density near the Fermi level increased after the process of crystallization took place. The electrical resistivity decrease recorded during the structural changes was due to an increase in the electron state density in the proximity of the Fermi level, as well as to an increase in the mean free path of the conducting electrons.