Provided are metal oxide varistors comprising a sintered ceramic, in which the ceramic comprises, by weight, about 91.0% to about 97.0% ZnO, at least 0.3% Mn, at least 0.4% Bi, at least 1.0% Sb, and 0.50% or less Co. The metal oxide varistors as disclosed herein may exhibit reduced power dissipation, improved thermal stability, and may be produced at a lower cost relative to conventional MOV devices.

A ceramic material, a varistor and methods for forming a ceramic material and a varistor are disclosed. In an embodiment, a ceramic material includes ZnO as a main component and additives selected from the group consisting of an Al.sup.3+-containing solution, a Ba.sup.2+-containing solution, and at least one compound containing a metal element, wherein the metal element is selected from the group consisting of Bi, Sb, Co, Mn, Ni, Y, and Cr.

A ceramic material, a varistor and methods for forming a ceramic material and a varistor are disclosed. In an embodiment, a ceramic material includes ZnO as a main component and additives selected from the group consisting of an Al.sup.3+-containing solution, a Ba.sup.2+-containing solution, and at least one compound containing a metal element, wherein the metal element is selected from the group consisting of Bi, Sb, Co, Mn, Ni, Y, and Cr.

The present invention is directed to a varistor comprising a dielectric material comprising a sintered ceramic composed of zinc oxide grains and a grain boundary layer between the zinc oxide grains. The grain boundary layer contains a positive temperature coefficient thermistor material in an amount of less than 10 mol % based on the grain boundary layer.

The present invention is directed to a varistor comprising a dielectric material comprising a sintered ceramic composed of zinc oxide grains and a grain boundary layer between the zinc oxide grains. The grain boundary layer contains a positive temperature coefficient thermistor material in an amount of less than 10 mol % based on the grain boundary layer.

A field grading composite body includes a polymeric matrix and a particulate filler distributed within the polymeric matrix. Particles of the particulate filler include a core formed from a semiconductor material, an oxide mixed layer deposited on the core, and conducting oxide layer. The conducting oxide layer deposited on the oxide mixed layer to provide an electrical percolation path through the polymeric matrix triggered by strength of an electric field extending through the field composite body. Conductors and methods of making field grading composite bodies for conductors are also described.

In an embodiment a ceramic material includes ZnO as main constituent, Y as a first additive, second additives including at least one compound containing a metal element, wherein the metal element is selected from the group consisting of Bi, Cr, Co, Mn, Ni and Sb, Si.sup.4+ as a first dopant and second dopants having at least one compound containing a metal cation from Al.sup.3+, B.sup.3+, or Ba.sup.2+, wherein a corresponds to a molar proportion of Bi calculated as Bi.sub.2O.sub.3, b corresponds to a molar proportion of Y calculated as Y.sub.2O.sub.3, c corresponds to a molar proportion of Al calculated as Al.sub.2O.sub.3, d corresponds to a molar proportion of Ba calculated as BaO, e corresponds to a molar proportion of B calculated as B.sub.2O.sub.3, f corresponds to a molar proportion of Si calculated as SiO.sub.2, g corresponds to a molar proportion of Ni calculated as NiO, h corresponds to a molar proportion of Co calculated as Co.sub.3O.sub.4, i corresponds to a molar proportion of Cr calculated as Cr.sub.2O.sub.3, j corresponds to a molar proportion of Sb calculated as Sb.sub.2O.sub.3, and k corresponds to a molar proportion of Mn calculated as Mn.sub.3O.sub.4.

In an embodiment a ceramic material includes ZnO as main constituent, Y as a first additive, second additives including at least one compound containing a metal element, wherein the metal element is selected from the group consisting of Bi, Cr, Co, Mn, Ni and Sb, Si.sup.4+ as a first dopant and second dopants having at least one compound containing a metal cation from Al.sup.3+, B.sup.3+, or Ba.sup.2+, wherein a corresponds to a molar proportion of Bi calculated as Bi.sub.2O.sub.3, b corresponds to a molar proportion of Y calculated as Y.sub.2O.sub.3, c corresponds to a molar proportion of Al calculated as Al.sub.2O.sub.3, d corresponds to a molar proportion of Ba calculated as BaO, e corresponds to a molar proportion of B calculated as B.sub.2O.sub.3, f corresponds to a molar proportion of Si calculated as SiO.sub.2, g corresponds to a molar proportion of Ni calculated as NiO, h corresponds to a molar proportion of Co calculated as Co.sub.3O.sub.4, i corresponds to a molar proportion of Cr calculated as Cr.sub.2O.sub.3, j corresponds to a molar proportion of Sb calculated as Sb.sub.2O.sub.3, and k corresponds to a molar proportion of Mn calculated as Mn.sub.3O.sub.4.

In an embodiment a multilayer varistor includes a ceramic body made from a varistor material, wherein the ceramic body includes a plurality of inner electrodes, first regions and second regions, wherein the varistor material in the first regions has a first average grain size D.sub.A, wherein the varistor material in the second regions has a second average grain size D.sub.B, and wherein D.sub.A<D.sub.B.

A chromaticity of zinc oxide is measured. The durability of a zinc oxide varistor is evaluated based on the chromaticity. This provides a varistor with a high durability stably.