# Diffusion coefficient.

1. Feb 29, 2008

### tkjacobsen

[SOLVED] Diffusion coefficient.

Hi everybody

I have a Nitrogen atom sitting at the octahedral site in fcc iron. I have calculated the minimum energy path (diffusion path) when moving the Nitrogen atom to the neighboring octahedral site.

My question is:
How can i calculate the diffusion coefficient? (only considering the diffusion in that one direction)

2. Feb 29, 2008

### Mapes

Hi tkjacobsen, welcome to PF. The standard way is to estimate $D$ for interstitial diffusion is

$$D=\frac{r^2 \nu}{6} \exp\left(\frac{-G_m}{kT}\right)$$

where $r$ is the distance between sites, $\nu$ is the attempt frequency (the characteristic vibration frequency in the crystal), and $G_m$ is the energy barrier involved in jumping from one interstitial site to another.

Edit: Sorry, I really should have given a reference. Try Allen and Balluffi's Kinetics of Materials, Porter and Easterling's Phase Transformations in Metals and Alloys, or any good kinetics book.

Last edited: Feb 29, 2008
3. Feb 29, 2008

### tkjacobsen

Thanks alot, this was exactly what I was looking for.

Best Regards
T.