Melting - Melting Criteria

Melting Criteria

Among the theoretical criteria for melting, the Lindemann and Born criteria are those most frequently used as a basis to analyse the melting conditions . The Lindemann criterion states that melting occurs because of vibrational instability, e.g. crystals melt when the average amplitude of thermal vibrations of atoms is relatively high compared with interatomic distances, e.g. <δu2>1/2 > δ_LR_s, where δu is the atomic displacement, the Lindemann parameter δ_L ≈ 0.20...0.25 and R_s is a half of the inter-atomic distance. The Lindemann melting criterion is supported by experimental data both for crystalline materials and for glass-liquid transitions in amorphous materials. The Born criterion is based on rigidity catastrophe caused by the vanishing elastic shear modulus, e.g. when the crystal no longer has sufficient rigidity to mechanically withstand load.