What is the Difference Between Self Diffusion and Interdiffusion

The key difference between self diffusion and interdiffusion is that self diffusion refers to the atomic migration in pure metals when all the atoms in the crystal structure that exchange positions are of the same type, whereas interdiffusion refers to the diffusion of atoms of one metal into another metal.

Self diffusion describes the change in the position of the atoms in a crystal. Interdiffusion, on the other hand, can be described as the diffusional exchange of atoms across two materials that are in contact. Usually, the self-diffusion process is comparatively slower than the interdiffusion process, while interdiffusion is faster than many other diffusion processes that can take place in a crystal lattice.

CONTENTS

1. Overview and Key Difference
2. What is Self Diffusion  
3. What is Interdiffusion
4. Self Diffusion vs Interdiffusion in Tabular Form
5. Summary – Self Diffusion vs Interdiffusion 

What is Self Diffusion?

Self diffusion describes the change in the position of the atoms in a crystal. Typically, self diffusion occurs by a vacancy mechanism. We can use a parameter called the diffusion coefficient, which measures the mobility of diffusing species. The presence of native point defects is useful in this type of diffusion process. This means self diffusion in semiconductors is usually mediated by native point defects. These defects include vacancies and self-interstitials.

The self-diffusion coefficient is the diffusion coefficient D_i* of the species i when the chemical potential gradient is equal to zero. The equation that links these parameters is as follows:

D_i* = D_i(∂lnc_i/∂lna_i)

In the above equation, a_i refers to the activity of the species i in the solution, while c_i is the concentration of i. Commonly, we assume that this term is equal to the tracer diffusion that is determined by observing the movement of an isotope in the material of interest.

What is Interdiffusion?

Interdiffusion can be described as the process of the diffusional exchange of atoms across two materials that are in contact. This type of diffusion is conducted by the chemical potential gradient across the boundaries. In simple words, interdiffusion is the diffusion of atoms of one metal into another metal.

Interdiffusion usually occurs through a retentive interface that is created within dentine by the penetration of an adhesive restorative resin. This interface lies between the applied resin composite material and the deep resin-free dentine. Generally, interdiffusion is faster than self-diffusion and vacancy diffusion. This is because the bonding of interstitials to the surrounding atoms is typically weaker, and there are many more interstitial sites in the interface of the interdiffusion process compared to a vacancy site to jump to.

What is the Difference Between Self Diffusion and Interdiffusion?

Self diffusion describes the change of the position of the atoms in a crystal. Meanwhile, interdiffusion is the process of diffusional exchange of atoms across two materials that are in contact. The key difference between self diffusion and interdiffusion is that self diffusion refers to the atomic migration in pure metals when all the atoms in the crystal structure that exchange positions are of the same type, whereas interdiffusion refers to the diffusion of atoms of one metal into another metal.

The below infographic presents the differences between self diffusion and interdiffusion in tabular form for side by side comparison.

Summary – Self Diffusion vs Interdiffusion

There are different types of diffusions that can take place in crystal lattices, such as self diffusion and interdiffusion. The key difference between self diffusion and interdiffusion is that self diffusion refers to the atomic migration in pure metals when all the atoms in the crystal structure that exchange positions are of the same type, whereas interdiffusion refers to the diffusion of atoms of one metal into another metal.

Reference:

1. “Diffusion and Kinetics.” Wright.edu.

Image Courtesy:

1. “Reaction-difusion patterns” By Gnomo4453 – Own work (CC BY-SA 4.0) via Commons Wikimedia

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