The mechanism of deformation under the indentation of MgO crystals has been studied by transmission and scanning electron microscopy. The dislocation structure and Burgers vectors of rosette dislocations are determined. The nature and geometry of cathodoluminescence around indentation have been also investigated. The luminescence radiation is shown to be caused by interstitial point defects built up under indentation.
The investigation by electron microscopy of the relief change after indentation reveales new peculiarities of the plastic deformation in NaCl crystals. The formation of hillocks near the indentation and on a lateral surface was observed. The hillocks are oriented in 〈110〉 directions, coinciding with the directions of chains of similar ions in the crystal. The formation of hillocks may be explained by the motion of interstitial ions by means of crowdions, their coagulation into prismatic dislocation loops, and their emergence at the surface by means of the joint action of prismatic slip and climb.
, on the occasion of his 65th birthday During concentrated load deformation of corundum basal plates a t room temperature dislocations are formed near the impression in (OOOl), {llZO}, and {1211} planes. However, these dislocations near the impression are not numerous. Thus the formation of an impression of the indenter cannot be ensured by such dislocations. I n this case, according to Indenbom's hypothesisl), the substance from under the indenter can be outflowed by dynamic crowdions. The deformation of a crystal is essentially accomplished a t the expense of origination of dynamic crowdions running in the (1100) directions in which oxygen ions are close packed. As a result this region of the crystal is enriched by interstitial oxygen ions. During heating of the crystal a coagulation of interstitial ions takes place and a great number of dipoles and loops appears around the impression in (0001) and {lIOO} planes.
It is shown that the sensitivity of the plane wave X‐r ay diffraction topography to the microdefects in Si single crystals is increased in the asymmetric reflection. Smaller microdefects are revealed as compared with the symmetric reflections. The components of elastic fields of large microdefects are investigated with aid of asymmetric reflections having various orientations of the diffraction vectors. The observed images are compared with the computer simulated ones. The simultaneous existence of the microdefects of vacancy and interstitial type in the specimen is shown. The misfit volume of the microdefects can be localized or distributed over its volume causing no strong local distortions. Possibilities for the microdefect generation during the SiO2 precipitation are discussed.
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