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Fully Dense, Fine‐Grained, Doped Zinc Oxide Varistors with Improved Nonlinear Properties by Thermal Processing Optimization
Author(s) -
Durán Pedro,
Tartaj Jesus,
Moure Carlos
Publication year - 2003
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2003.tb03470.x
Subject(s) - materials science , varistor , microstructure , grain boundary , spinel , grain size , sintering , zinc , doping , substructure , composite material , metallurgy , optoelectronics , physics , structural engineering , quantum mechanics , voltage , engineering
Fully dense, doped ZnO varistors were prepared using an easy two‐stage pressureless‐sintering method at temperatures as low as 825°C, with a grain size of ∼0.5 μm. After the highly nonohmic ZnO varistors were sintered, their fine microstructure consisted of uniformly sized grains, small spinel grains with partially dissolved manganese and cobalt oxides discontinuously distributed in the fairly wide grain boundaries, and an intergranular layer of bismuth‐rich crystalline phase mainly detected at three or four ZnO grain junctions. There were twins near the middle of almost all the ZnO grains. The abnormally high nonlinear properties of the almost nanostructured varistors ( F B ≈ 6–8 kV/mm and α= 270) were attributed to a uniform and very fine microstructure, a high ZnO–ZnO grain direct contacts concentration, and a uniform hybrid layer substructure (grain boundaries and twin boundaries) with different (but probably accumulative) potential barriers.