Absence of defect clusters in electron irradiated boron carbide

Abstract

Abstract Samples of boron carbide of differenct compostions wre irradiated and observed in a high voltage electron microscope (T.E.M.) at 100 keV, at 300K and 80 K. In spite of the high displacement rates (∼10−3d.p.a./s), the high doses (3 d.p.a.) and the low temperature, no bulk damage was observable in any of these samples either in form of defect clusters on the images or in form of important changes on the the diffraction patterns (phase transformations or Bragg spots broadening). The same observations has been done in samples of β rhomboheral boron and boron oxide irradiated by 800 keV electrons at 300 K and 15K at doses up to 2.3 d.p.a. The absence of clustering is not an absence of damage. These materials can accept vacancies and interstitial atoms in large number and in stable forms. The reason of the adaptation of these kind of structures to point defects in large concentration are discussed in relation with the existence of structural elements like icosahedra and rhombohedra.