The addition of transition metal elements, such as Co, is essential in realizing high non-linear ZnO-based varistors. The relation between the oxidation state of Co ions and the appearance of non-linear I-V characteristics was studied in ZnO-PreOn-based compositions. Pressed bodies were sintered at, 1430°C in oxygen to produce crystals 100 μ m in diameter, which were then annealed at various temperatures in air. The I-V characteristics of these specimens were then measured. The appearance and disappearance of non-linear I-V characteristics were found to occur reversibly depending on the annealing temperature and to be closely related to the oxidation state of the Co ions. This result is concurrent with calculations conducted using the DV-X a cluster method in which the Co ions promoted and stabilized the adsorption of oxygen atoms at ZnO to form surface (interface) states.
|Number of pages||8|
|Journal||Key Engineering Materials|
|Publication status||Published - 1999 Jan 1|
ASJC Scopus subject areas
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering