Phase development in ZnO varistors. (January 2015)

• Record Type: Journal Article
• Authors: Fan, J.; Poosimma, P.; Freer, R.
• Is Part Of: Advances in applied ceramics. Volume 114:Number 1(2015)
• Page Start: 14
• Page End: 17
• Publication Date: 2015-01
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1179/1743676114Y.0000000179
• Languages: English
• ISSNs: 1743-6753

Abstract

<abstract> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>Based on a typical ZnO varistor composition (97·0 mol.-% ZnO, 1·0 mol.-% Bi₂O₃, 1·0 mol.-% Sb₂O₃, 0·5 mol.-% MnO and 0·5 mol.-% Co₃O₄), phase development of the ZnO varistor during sintering has been investigated using <italic>in situ</italic> high temperature X-ray diffraction up to 900°C, and conventional ambient X-ray diffraction for samples sintered at 900°C to 1250°C. The results indicate that α-Bi₂O₃ can be detected until 700°C; the pyrochlore phase can be detected in the samples heat treated at 700°C and up to 1250°C; the spinel phase is present at and &gt;900°C. However, the main phases in the varistor are established by 950°C. By this temperature, the essential microstructure features are formed, and the varistors exhibit non-linear electrical properties, with a non-linear coefficient α of 35 and breakdown field of 8000 V cm⁻¹. With increasing sintering temperature, both the α value and breakdown field decrease.</p> </abstract>