Year: 2012
Type: book-chapter
Abstract: Mass action calculations (Lagerlöf & Grimes, 1998) have shown that the relative concentrations of extrinsic defects (point defects and defect associations) depend on the equilibrium temperature under which they are created.In sintered alumina, they can be determined by the sintering temperature and time, i.e. isothermal part of the firing schedule. Association of point defects with charges) can be associated with electrons (or holes) to form F centers (or V centers).In fact, upon trapping one electron (or two electrons), O V •• becomes a F + center (or a F center).Anionic vacancies can also be associated with a substitutional divalent cation ' Al M to form F cation center (such as F Mg or F Ca ).The F, F + and F cation act as a donor centers.The energy levels of F and F + are respectively estimated around 3 and 3.8 eV below the edge of the conduction band (Kröger, 1984). Extended defects: Grain boundariesGrain boundaries are the interfaces between like crystals, at which atomic planes are always disrupted to some extent.The atomic order of the lattice is preserved up to within approximately a unit cell of the dividing plane.Thus, the disordered region of a grain boundary is typically only 0.5-1 nm wide, although it does vary somewhat with the type of boundary and the crystal lattice periodicity.Grain boundaries provide segregation sites for impurities and defects.
Source: InTech eBooks
DOI: 10.5772/33719
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W1496523780