Microstructural and nonohmic properties of ZnO.Pr6O11 CoO polycrystalline system

The microstructure and electrical properties of varistors composed of (95-x) ZnO + x Pr 6 O 11 + 5 CoO (ZPC), (x = 0.1, 0.5 and 1.0) and sintered at 1300 and 1350 °C, were investigated. According to X-ray diffraction, several phases (ZnO, Pr 2 O 3 and Pr 2 CoO 4 ) are present when x = 1.0. Using Scanning Electron Microscopy, all of these compositions contain precipitates. These phases are important regarding the development of the microstructure and the electrical properties. The samples with x = 0.1 introduce the best nonohmic behavior (α = 9.0), however when x = 0.5 the electrical properties are highly degraded due to the small quantity of effective barriers. The density of superficial states N IS and donor concentration Nd decreases with Pr 6 O 11 addition. The decrease in the donor concentration is attributed to the annihilation of the donor defects according to the transformation of praseodymium oxides from Pr 6 O 11 to Pr 2 O 3 .

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