Experimental evaluation of the Peierls stresses in a variety of crystals and their relation to the crystal structure

Peierls stresses (τP) of dislocations of 66 slip systems in 52 crystals were estimated from experimental data either by direct extrapolation of the critical resolved shear stress (τc) vs. temperature curve to absolute zero temperature, or from the T0 value at which the temperature dependence of τc vanishes, based on the kink-pair formation enthalpy, which is a function of τP, described by the line tension model of the dislocation. The normalized τP/G (G is the shear modulus) values are distributed over four orders of magnitude, but τP/G values for a group of crystals with the same crystal structure are within an order of magnitude, indicating a homologous nature of τP in crystals. In order to compare the results with the Peierls-Nabarro (P-N) formula generalized to any dislocation character, log(τP/G) values were correlated with crystal parameters. In this generalized P-N plot, most of the plots deviate downwards from the Huntington relation (a revised, original P-N relation) and the results of the discretized P-N models of Ohsawa et al. (Ohsawa K, Koizumi H, Kirchner HOK, Suzuki T. Philos Mag A 1994;69:171), with the deviation becoming larger at large h/δ value, where h is the lattice spacing of the glide plane, and δ is the period of the lattice in the direction of the dislocation glide. In the plot, there is a tendency that the stronger the covalent character, the higher the τP/G value, reflecting the general tendency of the normalized theoretical shear strength of crystals.