Theory of regular arrays of defects: The void lattice
Defects in crystals may form a regular array, rather than a random distribution. The lattice of voids produced in irradiated molybdenum is a remarkable example of this. We give a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice. The existence of the void lattice depends on the elastic interaction between voids. The present approach can treat both arbitrarily anisotropic elastic continua and discrete lattices, and is readily extended to discuss the stability of the defect lattice. The results predict that a void lattice should occur in molybdenum, and compare a number of models for the void. Stability against shear of the void lattice is not discussed in the present paper. The ratio of the void lattice spacing to void radius predicted is 2.2 to 4.5 and is smaller than the value of about 10 observed. The results are in general agreement with the more approximate Malen-Bullough treatment.
Anion voidage and the void superlattice in electron irradiated Caf2
Abstract Anion voidage and anion void lattice formation in electron irradiated (100 keV–1 MeV) fluorite (CaF2) has been investigated by in situ transmission electron microscopy. At low fluences (≲1 dpa) the damage consists of randomly distributed anion voids and large bubble-like defects associated with fluorine gas. At higher fluences (≳ 1 dpa) the anion voids form a three-dimensional ordered superlattice with a simple cubic structure, whose axes are commensurate with those of the matrix. The superlattice has a unit cell parameter A0 in the range 15–30 nm and a ratio A0/R(superlattice parameter/anion void radius) in the range 3–6. The fully ordered superlattice “crystallizes” from randomly distributed anion voids by an ordering process in which locally ordered areas grow together after a fashion similar to that of epitaxy, leaving distorted superlattice regions between individual, fully ordered blocks. The basic radiation damage events are radiolytic and confined to the anion sublattice. Damage processes...
Resistivity of Interstitial Atoms and Vacancies in Copper
The residual resistivity associated with the presence of interstitial atoms or vacancies in copper is studied with particular attention devoted to the scattering of conduction electrons resulting from lattice distortions surrounding the imperfections. For interstitials this scattering is found to be an order of magnitude larger than that from the defect itself. For vacancies it is smaller but still important. Interference between scattering from the defect and the surrounding lattice distortion is computed and found to be very small. The calculated resistivity associated with one atomic percent of interstitial atoms is 10.5 \ensuremath{\mu}ohm cm. The corresponding value for vacancies is 1.5 \ensuremath{\mu}ohm cm. Using nominal values for the energy of formation of these defects, the stored energy to resistivity ratios associated with interstitials, vacancies, and interstitial-vacancy pairs are 1.4, 3.4, and 1.6 cal/g per \ensuremath{\mu}ohm cm, respectively.