Microstructure and Crystal Phases of Praseodymium Oxides in Zinc Oxide Varistor Ceramics

Abstract

The effect of sintering temperature on the microstructure and crystal phases of the intergranular praseodymium oxides in ZnO varistor ceramics was investigated using transmission electron microscopy and high‐resolution electron microscopy. The ZnO grains were three‐dimensionally separated from the intergranular praseodymium oxides. On the basis of microdiffraction analyses of the intergranular layer, the phase transformation from fcc‐Pr6O11 into hcp‐Pr2O3 was found when the sintering temperature increased from 1300° to 1350°C. The defect reaction equation and the decrease of donor concentration with increasing sintering temperature can verify the certainty of phase transition during the liquid‐phase sintering observed by transmission elecron microscopy. Additionally, on the basis of the small variations of the breakdown voltage per grain boundary, the number of active grain boundaries is not a dominant factor for the donor concentration dependence on the sintering temperature.

Pulse aging behavior of ZnO–Pr6O11–CoO–Cr2O3–Dy2O3 varistor ceramics with sintering time

“…Zn-Pr-based varistors have been studied to further enhance varistor properties and the stability against various stresses, compared to Zn-Bi-based varistors. Most investigations on Zn-Pr-based varistors have been reported on the microstructure and electrical properties in terms of additives and sintering processing [6][7][8][9][10][11][12][13][14][15][16]. In particular, Nahm et al reported the effect of rare earth oxides and lanthanum oxide on electrical properties and its stability against DC accelerated degradation stress [9][10][11][12][13][14][15][16][17].…”

“…Furthermore, it also deteriorates the surge absorption capabilities due to a decrease of effective grain boundary area. To overcome these problems, Zn-Pr-based varistors have been actively studied [6][7][8]. Zn-Pr-based varistors have been studied to further enhance varistor properties and the stability against various stresses, compared to Zn-Bi-based varistors.…”

Electrical behavior against current impulse in ZnO–Pr6O11-based varistor ceramics with terbium addition

“…Many investigations for ZnO-Pr 6 O 11 -based varistor ceramics have been reported on the microstructure and electrical properties in terms of additives, and sintering temperature and time [4][5][6][7][8][9][10][11][12][13][14][15]. In particular, the effect of rare earth oxides (Pr 6 O 11 , Er 2 O 3 , Dy 2 O 3 , Tb 4 O 7 , etc) on electrical properties and its stability [7][8][9][10][11][12][13][14].…”

Microstructure and Electrical Properties of ZPCCYT Varistor Ceramics

“…ZnO-Pr 6 O 11 -based varistor ceramics have been studied to further enhance the varistor properties [5][6][7][8][9][10][11]. Nahm et al reported that Zn-Pr-Co-Cr (ZPCC)-Rare earth oxide (R = Er, Y, Dy, etc.…”