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

	Essentially we have two rather direct methods			3    ∆l l  –  ∆a a     =   cV  –  ci
		Differential Thermal Expansion (or ∆l/ l- ∆a/a -method).
		.Positron annihilation
	Both methods will not give results if the vacancy concentration at the melting point is below, roughly, 10–7.
		<τ>  =  τ2 · 1 + τ2ν · cV 1 + τ1ν · 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)