Dipole Tensors and Volume Changes of Point Defects in H.C.P. Lattices

Abstract

By computer simulation techniques dipole tensors and relaxation volumes of point defects in h.c.p. lattices are calculated for the fully relaxed lattice. Short‐range pair interatomic potentials to represent Mg and α‐Zr are used. Calculations for the vacancy at its equilibrium and activated states are reported. Quantitative differences due to the material elastic properties are found. For self interstitials, dipole tensor symmetries and volume‐change values are analyzed taking into account the defect‐lattice symmetries.

Elasticity of Solids with a Large Concentration of Point Defects

“…The radius of an oxygen vacancy is about 16 % smaller than that of the oxygen ion, whereas the radius of Gd 3+ is more that 7 % larger than that of Ce 4+ . The available data on other systems [1,[5][6][7][8] point out that pairing of defects usually leads to a net volume change which is smaller than, but of the same order of magnitude as, those of the volume changes associated with the formation of individual defects. Thus, one would expect that the volume effect of the reaction given in Equation 17 expressed as a dimensionless parameter (relative volume change per mole fraction) would be of the order of magnitude bq 0 ≈ (r Gd 3+/r Ce 4+) 3 -1 = 0.2, where q 0 is the molar density.…”

“…The influence of point defects on the elastic properties of solids has been extensively investigated over the past few decades. [1][2][3][4][5][6][7][8] Attention has been primarily directed towards understanding the effects of local stresses induced by point defects. A relatively small concentration of point defects (< 10 20 cm -3 ) may strongly affect material properties that are of significant practical importance, such as critical strength and aging.…”

Analysis of accelerated irradiation growth in Zr-2.5% Nb pressure tubes

“…In this work we shall use the equilibrium and saddle-point dipole tensors reported by Monti (1991) (also A. M. Monti (1993, private communication) ) for vacancies and interstitials in Zr. More speci® cally, we shall use the results derived using her P6C2 pair potential, a spline ® t of six cubic polynomials adjusted to the Zr elastic constants and a vacancy formation energy of 1.8 eV.…”

“…The latter bias the rate of capture of vacancies and interstitials by dislocations, grain boundaries and cavities (Savino and Smetniansky-De Grande 1987, Smetniansky-De Grande et al 1988, 1991, Woo 1988). Namely, the atomic con® gurations of vacancies and interstitials in Zr are used for calculating the di usion coe cients of these defects and their dependence on the local stress.…”

Mechanical properties and defect chemistry

“…Since the introduction in the middle of the previous century of the concept of point defects in solids, attention has been nearly completely focused on two issues: location of the point defects with respect to the crystal lattice and their influence on mechanical and electrical properties [2][3][4][5][6][7][8][9]. It was quickly found that a relatively small concentration of these defects (b 10 20 cm − 3 ) could lead to significant changes in the critical strength and in the aging process [2][3][4]10].…”