Dislocations, Slip, and Fracture in BeO Single Crystals

Abstract

Dislocations formed during the growth and deformation of BeO single crystals were studied with x-ray and electron microscopy. The stresses for slip on the systems (0001) 〈112̄0〉, {101̄0} [0001], {101̄0} 〈112̄0〉, and {112̄2} 〈112̄3〉 are approximately 3.5×108, 1.1×109, 4.9×108, and >2.5×109 dyn/cm2, respectively, at 1000°C. Slip directions in deformed specimens were shown with x-ray microscopy. Defects in the specimens were shown to interfere with slip. Dislocation pinning and elastic interactions were observed in electron micrographs. These observations are correlated with theory.

Creep of Oxide Single Crystals

“…Three features are evident on the micrographs: slip steps in the crystal faces parallel to the basal planes, twinned regions, and cracks. Examination of the different faces of several twinned crystals iihdicates that the twin plane is consistent with a (0112} type (using the structural unit cell with c/a = 2.73), which agrees with previous results for sapphire (43). Most twins observed appeared to eminate from a crystal corner, anq were often associated with cracking.…”

Dislocations in Ceramics

“…Early studies on BeO single crystals by Bentle and Miller [51] identified four slip systems; basal slip, ð0001Þh11 20i; prismatic slip, f1 100gh11 20i and f1 100g½0001; and pyramidal slip, f 1 122gh11 23i. Not surprisingly, significant plastic anisotropy was found.…”

Direct observation of dislocation motion in ZnO

“…p o r t 4 for Cds by Oaipiyan and Savchenko (1). The deformation behaviour of ZnO single crystals having the wurtzite structure has been investigated in some detail by Carlsson and Svensson (2 to 4); the basal slip ie more active than the prismatic slip in the room temperature region in the darkness , but the former becomes markedly inactive with the illumination of light while the latter remain unchanged, resulting in less activity in the basal slip than the prismatic slip under illumination (4) * Some direct observations of dislocations in the wurtzite lattice by transmiasion electron microscopy have been reported for CdS (5, 6), Be0 (7,8), and ZnO (9), but the knowledge on the nature of dislocations in this lattice, especially on their detailed behaviour under stress. is still poor.…”