This mean distance ⟨ ⟨ r 2 ⟩ ⟩ → → 0 tends to zero for low temperatures – dislocations will annihilate and the crystal is free of defects. The expression diverges ⟨ ⟨ r 2 ⟩ ⟩ → → ∞ ∞ , if the denominator tends to zero. This happens, when Y ⋅ ⋅ a 4 π π k B T = 4 . A diverging distance of dislocations implies, that they are dissociated and do not form a bound pair. The crystal is molten, if several isolated dislocations are thermally excited and the melting temperature T m is given by Young's modulus: