Effects of Zr and Y Addition on the Electrical Degradation Characteristics of ZnO Varistors

Akiyama, Yuji; Takada, Masayuki; Fukumori, Ai; Sato, Yoshiaki; Yoshikado, Shinzo

doi:10.1541/ieejfms.130.394

Cited by 2 publications

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“…Figure 5 shows XRD diffraction patterns from the samples used in the present study. The diffraction peaks were classified as ZnO, Bi-Cr-O (Bi 16 CrO 27 ), Zn-Sb-O spinel, Zn 2 SiO 4 , and the R-phase. The peaks labeled R could be identified as being associated with the R-phase since these peaks were not observed for sample R0, and SEM observations identified no additional crystalline phases in the samples with rare earth additives.…”

Section: Resultsmentioning

confidence: 99%

“…This can be achieved by the addition of Sb or Si. It has also been shown that the addition of R 2 O 3 (R: rare earth element) leads to a reduction in the ZnO grain size and an increase in the varistor voltage [6][7][8][9][10][11][12][13][14][15][16]. It was reported that a new phase containing the rare earth element (referred to as the R-phase) segregates at ZnO grain boundaries.…”

Section: Introductionmentioning

confidence: 99%

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Correlation between electrical properties and crystalline phases for ZnO-Bi2O3 based varistor ceramics with rare earth additives

Kato

Takada

2013

J Electroceram

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In this study, the correlation between the electrical properties and crystalline phases of ZnO-Bi 2 O 3 based varistor ceramics with rare earth additives was investigated. The additives used were in the form R 2 O 3 , where R represents Eu, Ho, Y, Er, Yb, or Lu. It was found that the incorporation of rare earth additives led to an increase in the varistor voltage in the nonlinear region, an increase in the leakage current in the pre-breakdown region, and a reduction in the limiting voltage in the upturn region. In the sample with added Y 2 O 3 , a phase referred to as the R-phase, which contained Y, Bi, Sb, Zn, Mn, and O, was observed to be homogeneously distributed at ZnO grain boundaries. X-ray diffraction analysis revealed that the amount of the Zn-Sb-O spinel and Bi-Cr-O phases present was reduced by the rare earth addition, and that rare earth elements were incorporated into a common crystalline phase. It is suggested that the formation of the R-phase at ZnO grain boundaries and the reduction in the Bi 2 O 3 liquid phase during the sintering process might be responsible for suppressing ZnO grain growth, thus leading to an increase in the varistor voltage.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Correlation between electrical properties and crystalline phases for ZnO-Bi2O3 based varistor ceramics with rare earth additives

Kato

Takada

2013

J Electroceram

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Effects of Sb, Zr, or Y addition on Electrical Degradation Characteristics of ZnO Varistors

et al. 2011

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The effects of amount of Sb added to Bi-Mn-Co-Sb-Si-Cr-Ni-Zr-added ZnO varistors on the tolerance characteristics of electrical degradation were investigated. Furthermore, the effects of addition of both Zr and Y to Bi-Mn-Co-Sb-Si-Cr-Ni-added ZnO varistors (the same composition as one of commercial varistors) on the varistor voltage and leakage current were investigated.ZnO varistors were fabricated by adding Bi 2 O 3 , MnO 2 , Co 3 O 4 , Cr 2 O 3 , NiO, SiO 2 as a basic additives, Y 2 O 3 of 0 -1.0 mol% (Y of 0 -2.0 mol%), or Zr of 0 -0.6 mol% and Sb 2 O 3 of 0 -2.5 mol%, as extra additives to ZnO. Pressed powders were calcined at 600ºC for 5 h in air and sintered at 1150ºC for 3 h in air. Aluminum electrodes were applied to two end faces to measure the voltage-current (V-I) characteristics. The electrical degradation was carried out by applying a dc current of 100 mA/cm 2 in N 2 atmosphere for 30 min. The nonlinearity index α and the standup voltage of V-I characteristic were estimated. The composition of elements in a sample was analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The crystal structure was analyzed by X-ray diffraction (XRD).Values of nonlinearlity index a bef and a deg before and after the electrical degradation, respectivly, are shown in Fig. 1. It was found that addition of Sb enhances the tolerance characteristics to the electrical degradation and the amount of Sb 2 O 3 addition of approximately 1 mol% of is the optimal. When the amount of added Sb increased, the amount of existence of a Zn 2.33 Sb 0.67 O 4 -type spinel particle evaluated from XRD as shown in Fig. 2 increased, because the amount of existence of Zr compound increased similarly. It was suggested that Zr compound was also related to the electrical degradation characteristic.Varistor voltage decreases a little when the amount of added Zr increases in simultaneous addition of Zr and Y. On the other hand, the value of nonlinearlity index hardly changed. Without Zr, the increase in the leakage current accompanying the increase in the amount of added Y, which has been reported conventionally, was not found in this study as shown in Fig. 3. However, adding Zr of approximately 0.2 -0.45 mol%, the leakage current increased by adding Y of more than 1 mol% and adding Zr of approximately 0.6 mol%, it decreased.

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Effects of Zr and Y Addition on the Electrical Degradation Characteristics of ZnO Varistors

Cited by 2 publications

References 12 publications

Correlation between electrical properties and crystalline phases for ZnO-Bi2O3 based varistor ceramics with rare earth additives

Correlation between electrical properties and crystalline phases for ZnO-Bi2O3 based varistor ceramics with rare earth additives

Effects of Sb, Zr, or Y addition on Electrical Degradation Characteristics of ZnO Varistors

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