MODEL AND THEORY FOR THE DETERMINATION OF DIFFUSION-COEFFICIENTS BY AUGER-ELECTRON SPECTROSCOPY MEASUREMENTS AND AN APPLICATION TO OXYGEN DIFFUSION ALONG THE [0001] AND [10(1)OVER-BAR0] AXES IN SINGLE-CRYSTAL ZIRCONIUM

A simple hopping model of the diffusion of adsorbed species from a surface into the bulk of a material has been formulated and served mathematically. The difference in the energy barriers for an atom moving between the atomic layers at the surface and in the bulk are explicitly considered. This model is also capable of describing the initial stages of diffusion, something that conventional solutions of the continuum diffusion equation cannot handle. Auger electron spectroscopy has been used to measure the dissolution rate of oxygen from Zr(0001) and Zr(10 ($) over bar 10) surface into the bulk. Satisfactory results were obtained by applying our model to the diffusion data for these two zirconium surfaces for two different heating schedules: (i) rapid temperature ramp-and-hold and (ii) continuous linear heating with respect to time. The resulting Arrhenius expressions for diffusion are: D = (0.115 +/- 0.031) exp[(-44.45 +/- 4.82) kcal/RT] cm(2)/s along Zr[0001] and D = (1.07 +/- 0.26) exp[(-46.18 +/- 4.22) kcal/RT] cm(2)/s along Zr[10 ($) over bar 10].