Tape casting and properties of Pr2O3-doped ZnO multilayer varistors.

Purpose – This paper aims to fabricate and characterize ZnO-based multilayer varistors. Design/methodology/approach – Tape casting technique was utilized for preparation of multilayer varistors based on ZnO doped with Pr, Bi, Sb, Co, Cr, Mn and Si oxides. Scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) methods were used to study the microstructure, elemental and phase compositions, respectively, of the varistors. Dielectric properties were investigated by impedance spectroscopy. Current–voltage (I–U) dependences were measured to characterize nonlinear behavior of the fabricated varistors. Findings – XRD, SEM and EDS studies revealed dense microstructure of ceramic layers with ZnO grains sized 1-4 μm surrounded by nanometric Bi-rich films, submicrometer Zn7Sb2O12 spinel grains and needle-shaped Pr3SbO7 crystallites. Praseodymium oxide was found to be very effective as an additive restricting the ZnO grain growth. I–U characteristics of the fabricated multilayer varistors were nonlinear, with the nonlinearity coefficients of 23-27 and 19-51 for the lower and higher Pr2O3 content, respectively. The breakdown voltages were 60-150 V, decreasing with increasing sintering temperature. Originality/value – Low-temperature cofired ceramics technology enables attaining a significant progress in miniaturization of electronic passive components. Literature concerning application of this technology for multilayer varistors fabrication is limited. In the present work, the results of XRD, SEM and EDS studies along with the I–U and complex impedance dependences are analyzed to elucidate the origin of the observed varistor effect. The influence of sintering temperature and Pr2O3-doping level was investigated. [ABSTRACT FROM AUTHOR]