Abstract
ZnO varistor materials were prepared by a sol gel route with subsequent drying and calcination. Varistor discs fabricated from these materials were subjected to a two step sintering schedule. Therefore in a typical experiment, the samples were heated to 1000°C, then allowed to cool for over 30 min to 900°C and held there for 6 h. The results were compared with commercial varistor samples sintered in a similar way. Considerably higher breakdown voltages were obtained for the varistors made from nanosample (1192±30 V mm−1) compared with the commercial samples (723±30 V mm−1) sintered under the same experimental conditions. The sintered materials were characterised by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and density measurements.
Highlights
ZnO varistors are used as surge suppressors in most of the areas of electronic and communication technologies.[1,2,3,4,5] These are conventionally prepared from ZnO and other additives (Bi2O3, Sb2O3, CoO, MnO, Cr2O3, NiO and Al2O3) using a solid state reaction by plastification, pelletisation and sintering.[1,2] The pressed discs are sintered at 1100–1250uC
Almost the same densification was obtained for nanovaristors sintered by conventional or step sintering procedure
Field emission scanning electron microscopy studies show that average grain sizes of 1.60¡0.05 and 2.00¡0.05 mm have been obtained by step sintering and conventional sintering techniques respectively
Summary
ZnO varistors are used as surge suppressors in most of the areas of electronic and communication technologies.[1,2,3,4,5] These are conventionally prepared from ZnO and other additives (Bi2O3, Sb2O3, CoO, MnO, Cr2O3, NiO and Al2O3) using a solid state reaction by plastification, pelletisation and sintering.[1,2] The pressed discs are sintered at 1100–1250uC. They are characterised by a threshold voltage (breakdown voltage or Vc), where the transition from linear to non-linear mode occurs.[1,2] It is well known that the breakdown voltage of a sintered ceramic body is proportional to the number of grain and grain boundaries formed in between the electrodes.[5,7] A high performing device in a smaller dimension might be prepared by employing nanosize precursor materials.[5,6,7,8] nanoparticles can be sintered at a lower temperature compared with the coarse grained ceramics
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