On the calculations of the diffusion coefficients of oxygen and nitrogen in niobium

Abstract

The Snoek peaks for oxygen and nitrogen in niobium have been remeasured using a torsion pendulum equipped with LVDT transducers connected to an oscillograph for automatic data recording. The peak temperatures were determined using a new numerical analysis of the peak shape. These new low temperature data have been combined with high temperature direct data and intermediate temperature high frequency internal friction data reported in the literature. When it is assumed that the oxygen and nitrogen] occupied octahedral positions in the niobium matrix, the diffusion coefficients for both oxygen and nitrogen atoms follow a simple Arrhenius behavior. In the temperature range of this analysis (140 to 1000°C for oxygen and 270 to 1800°C for nitrogen) the equationsD = (5.3E - 7) exp - (1.095E5)/RT andD = (2.6E - 6) exp - (1.523E5)/RT apply for the diffusion of oxygen and nitrogen, respectively. Entropy of activation calculations were made using the above activation energies and frequency factors, and the results agree well with reported values for other systems as well as with the theory of Keyes. This good agreement suggests that the assumption that oxygen and nitrogen prefer octahedral sites is probably correct.