Microstructural origin of the dielectric breakdown strength in alumina: A study by positron lifetime spectroscopy

• Published in: Journal of the European Ceramic Society Vol. 25; no. 12; pp. 2813 - 2816
• Main Authors: Si Ahmed, A., Kansy, J., Zarbout, K., Moya, G., Liebault, J., Gœuriot, D.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 2005; Elsevier
• Subjects: Al 2O 3; Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric breakdown and space-charge effects; Dielectric properties; Dielectric properties of solids and liquids; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Engineering Sciences; Exact sciences and technology; Grain boundaries; Materials; Miscellaneous; Physics; Positron annihilation; Sintering; Technical ceramics; Grain boundaries; Positron annihilation; Sintering; Dielectric properties; Al 2O 3; Electrical properties; Experimental study; Oxide ceramics; Al2O3; Grain boundary; Technical ceramics; Property structure relationship; Manufacturing; Microstructure; Alumina
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2005.03.146

The dielectric breakdown strengths of two series of sintered alumina samples of low and high impurity content (with Si being the dominant element) and single crystal of low impurity level are compared with positron lifetime measurements. It is found that, in sintered alumina, the breakdown strength increases linearly with increasing concentration of positron traps at grain boundaries. These traps are likely clusters containing negatively charged cationic vacancies, which are induced by silicon dissolution into Al 2O 3. Therefore, the improvement of the breakdown strength can be traced to silicon segregation at grain boundaries. More precisely, it is deduced that the dissolution of Si impurity into Al 2O 3, when it is compensated by a cationic vacancy V Al ‴ , is responsible for such an improvement. A solubility of Si in Al 2O 3, achieved during the firing schedule of the sintering process, and which does not take into account enhanced solubility caused by mutual compensation of Si with lower valence foreign cations such as Ca and MgO, is estimated at 120 ppm.