(Co, Nb, Sm)‐Doped Tin Dioxide Varistor Ceramics Sintered Using Nanopowders Prepared by Coprecipitation Method

Abstract

Co, Nb, Sm)-doped SnO 2 -based ceramic with varistor characteristics was successfully fabricated by a conventional sintering of nanosized (Co, Nb, Sm)-doped SnO 2 powders prepared by coprecipitation method. Values of aB38 and E B 5 1430 V/mm were obtained for the varistor doped with 0.05 mol % Sm 2 O 3 , sintered at 12001C for 1 h. Microstructure development was studied by scanning and transmission electron microscopy, elemental analysis, and X-ray diffraction. The mean grain size of the SnO 2 -based varistor was 1.75 lm. No other phase besides SnO 2 was observed in the varistor doped with 0.05 mol % Sm 2 O 3 . The presence of Nb, Co, and Sm inside the SnO 2 grains confirmed the formation of solid solution. No segregation of Nb was observed and Nb atoms were homogeneously distributed. The excess amounts of Co were segregated at triple-junctions between SnO 2 grains. A Sm-rich region with a typical thickness of 65 nm was observed at the grain boundary of the varistor.L. Levinson-contributing editor

Effects of Sr(Co, Nb, Ta)O3 addition on the defect structures and electrical properties of ZnO-based varistors

“…The segregation of Co and Mn ions near the grain boundary areas during sintering may be due to large elastic strains induced when smaller Co 3+ and Mn 3+ cations are reduced into divalent but larger Co 2+ and Mn 2+ . Such induced elastic straining may relax by segregation at the grain boundary region, as suggested by Bastami et al 30…”

Potential Barrier of (Zn,Nb)SnO2‐Films Induced by Microwave Thermal Diffusion of Cr3+ for Low‐Voltage Varistor

“…The origin of potential barrier has been investigated by some authors in an attempt to explain the mechanisms responsible for the electrical characteristics of the varistor ceramics based on SnO 2 . It is known that the potential barrier existing in the grain‐boundary region is dependent on the additives (amount and type of defects induced by them) and proportional to the nominal voltage of a varistor . The potential barrier is formed by SnO 2 intrinsic defects () as well by extrinsic defects created by the addition of modifying agents, as shown in Eqs.…”

“…It is known that the potential barrier existing in the grain-boundary region is dependent on the additives (amount and type of defects induced by them) and proportional to the nominal voltage of a varistor. 5,[7][8][9][10] The potential barrier is formed by SnO 2 intrinsic defects (V 00 Sn ; V 00 O ) as well by extrinsic defects created by the addition of modifying agents, as shown in Eqs. (2)(3)(4).…”

Microstructure and nonohmic properties of SnO2–Ta2O5–TiO2 varistor system doped with CuO

“…11 and 12) or Zn 2+ (Refs. 5,[13][14][15] are larger and insoluble ions that segregate at SnO 2 grain boundary regions to promote the densification by producing oxygen vacancies, and the modifiers, such as Cr 3+ , Fe 3+ and rare earth elements, [5][6][7][8]16 are effective to improve the electrical properties of the varistors.…”