Nonlinear electrical properties and aging characteristics of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (R = Y, Er) oxide-based varistors

The electrical properties and stability of the varistors, which composed of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (Y, Er) oxide-based ceramics, were investigated for different additives. The breakdown voltage of the varistors increased in order of NiO→undoped→MgO→Cr2O3: 1200→1551→1691→1959 V/cm for ZPCY system and undoped→NiO→MgO→Cr2O3: 1024→1041→1500→1668 V/cm for ZPCE system, respectively. The nonlinear coefficient value increased in order of undoped→NiO→MgO→Cr2O3: 21→25→38→50 in ZPCY system and NiO→undoped→MgO→Cr2O3: 27→32→35→38 in ZPCE system, respectively. In ZPCY and ZPCE systems, the Cr2O3-additives most greatly improved the nonlinear properties. In Cr2O3-doped system, ZPCY system exhibited higher nonlinear properties than that of ZPCE system. The stability against d.c. accelerated aging stress was higher in Cr2O3-additives than in NiO- and MgO-additives for ZPCY system and was higher in NiO-additives than in MgO- and Cr2O3-additives for ZPCE system.