### 4.1.2 Essentials to Chapter 4.1: Experimental Techniques for Studying Point Defects in Equilibrium

| Essentially we have two rather direct methods |  |
3 | æ ç è | D l l | – | D a a | ö ÷ ø | = | cV – ci
|  | Differential Thermal Expansion (or D l/ l- D a/a -method). |
|  | .Positron annihilation |
| Both methods will not give results if the vacancy concentration at the melting point is below, roughly, 10–7. |
<t> | = | t2 · | 1 + t2n · cV 1 + t1n · cV
--- | --- | --- | ---
| Most numbers for point defects in metals and some other crystals were obtained by these two methods. |
| There are many other methods, but always either limited to certain crystals, expensive, hard to evaluate, and so on. |  |
| In essence, there are still no reliable and undisputed numbers for, e.g., the formation and migration enthalpies for vacancies (and interstitials) in Si or other semiconductors like GaAs. |  |

© H. Föll (Defects - Script)