Influence of processing on microstructure and electrical characteristics of multilayer varistors

Abstract

The paper reports on the influence of processing on microstructure and electrical properties of multilayer varistors based on zinc oxide doped with Bi 2 O 3 , Sb 2 O 3 , Co 2 O 3 , MnO, Cr 2 O 3 , B 2 O 3 , and SiO 2. 0.5-1 wt% of AlF 3-CaB 4 O 7 was used as a new effective sintering aid. The behavior of green laminates during heating was characterized using differential thermal analysis and a heating microscope. As revealed by XRD, SEM, and EDS methods, the varistor layers are composed of ZnO grains of 1-5 μm size, submicrometer spinel and pyrochlore grains situated at the ZnO grain boundaries, and nanometric Bi 2 O 3-rich films surrounding ZnO grains. Complex impedance studies carried out in the frequency range of 0.01 Hz-2 MHz at temperatures changing from-30 to 150 ℃ imply the formation of semiconducting grains and insulating grain boundaries. Frequency dependence of dielectric permittivity shows a high plateau at lower frequencies, typical for barrier layer capacitance effect. The fabricated multilayer varistors show nonlinear current-voltage characteristics with a high nonlinear coefficient of 26-38. The breakdown voltage was found to decrease within the range of 66-130 V with sintering temperature increasing from 1000 to 1100 ℃. Good surge current capability of the varistors was confirmed by the tests using 8/20 μs pulses.

Fabrication and electrical characteristics of flash-sintered SiO2-doped ZnO-Bi2O3-MnO2 varistors

“…ZnO varistors have been successfully applied to the surge protector in electrical transmission and transient overvoltage or circuits to prevent lightning strikes due to their excellent nonlinearly electrical characteristics which originate from the grain boundaries [1]. It is generally believed that ZnO varistors are made by mixing zinc oxide powders with various oxide additives, such as Bi 2 O 3 [2,3], Sb 2 O 3 [4,5], Co 2 O 3 [6,7], Sc 2 O 3 [8], MnO 2 [9], Cr 2 O 3 [10,11], and TiO 2 [12]. At present, most ZnO-based varistors are prepared by a conventional sintering method.…”

“…At present, most ZnO-based varistors are prepared by a conventional sintering method. However, it needs high sintering temperature (about 1200 ℃) and long holding time (> 2 h), leading to high energy consumption [13,14]. Besides, the high sintering temperature may lead to the volatilization of some elements (like Bi), which in turn affect the varistor properties.…”

Flash Assisted Synthesis and Electrical Performance of MnO2-doped ZnO-Bi2O3-based Ceramics

“…ZnO-Bi2O3-based ceramics have been significantly applied to electrical power systems and microelectronics due to their excellent non-ohmic characteristic [1][2][3][4][5][6]. In general, the conventional sintering (CS) for the preparation of ZnO-Bi2O3-based ceramic always requires a higher furnace temperature of 1200 ℃ and a longer sintering time of >2 h, which suffered from some disadvantages, such as time, cost and energy waste [7].…”

Fabrication and electrical characteristics of flash-sintered SiO2-doped ZnO-Bi2O3-MnO2 varistors

“…ZnO varistors have been successfully applied to the surge protector in electrical transmission and transient overvoltage or circuits to prevent lightning strikes due to its excellent nonlinearly electrical characteristics which originated from the grain boundaries. [1] It is generally believed that ZnO varistors are made by mixing zinc oxide powders with various oxide additives, such as Bi2O3 [2,3], Sb2O3 [4,5], Co2O3 [6,7], Sc2O3 [8], MnO2 [9], Cr2O3 [10,11], and TiO2 [12]. In addition, ZnO as the addition can not only shift the tri-critical point to room temperature for the Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics, but also solve evaporation and hygroscopicity problem of K2O in the KNbO3 ceramics.…”