Influence of WO₃‐Doping on the Microstructure and Electrical Properties of ZnO–Bi₂O₃ Varistor Ceramics Sintered at 950°C

Abstract

The phase evolution, microstructure, and electrical properties of WO 3 -doped ZnO-Bi 2 O 3 -based varistors were investigated for different amounts x (0 ≤ x ≤ 1.60 mol%) of the dopant. When x was less than 0.40, the dissolved W 6+ in the b-Bi 2 O 3 acted as a donor in the grain boundaries and reduced the electrical properties of the ZnO varistors. However, when x was 0.40 mol%, which meant an amount of WO 3 equal to that of Bi 2 O 3 , the electrical properties dramatically increased, which means the W 6+ donor effect is removed at the grain boundaries because a new Bi 2 WO 6 phase was formed in the grain-boundary regions. The Bi 2 WO 6 phase has high oxygen conductivity at high temperatures; it transfers more oxygen to the grain boundaries in order to further enhance the electrical properties. For x values higher than 0.40 (i.e., an addition of WO 3 that is greater than the content of Bi 2 O 3 ), the electrical properties were steadily reduced in comparison to the composition with x = 0.40. This could be explained by the reduced amount of Co, Mn, and Al at the grain boundaries and in the ZnO grains as a result of their incorporation into the ZnWO 4 phase. The electrical properties of the ZnO grains and the grain boundaries were in agreement with the results of the impedance spectroscopy analysis. L. M. Levinson-contributing editor Manuscript No. 35357.

Research method and mechanism analysis of a novel high-performance quaternary Zn–Sr–Co–Sb varistor ceramic

“…Consequently, the substitution of Co 3+ ion for the site of Zn 2+ in the ZnO lattice reduces the lattice parameters according to Bragg's Law. 21 The diffraction peak of the quaternary system inversely shifts toward a smaller angle compared to the ternary system, which is in accordance with the increase in lattice parameters, indicating an increase in interplanar spacing of the ZnO phase. This can be interpreted that the Sb 3+ ( r = 0.76 Å) preferentially diffuses in the ZnO lattice and substitutes the site of Zn 2+ compared to Co 3+ .…”

The effect of SiO2on electrical properties of low‐temperature‐sintered ZnO–Bi2O3–TiO2–Co2O3–MnO2‐based ceramics

“…It should be noted that in Figure 1B, along with the increase in SiO 2 content from 0 to 6 wt%, the peaks of the Bi 2 O 3 shift to a higher angle, which indicates a decrease in the lattice parameter and cell volume according to Bragg's law. 37 This can be interpreted that Si 4+ (0.26 A) has a smaller ionic radius comparing to Ti 4+ (0.42 A), Mn 4+ (0.39 A), and Co 3+ (0.55 A), therefore it will diffuse in Bi 2 O 3 lattice preferentially and thus reduce the solubility of other ions.…”

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

“…Transition element oxides (TEOs) such as Co 2 O 3 [ 29 ], Co 3 O 4 [ 30 ], Cr 2 O 3 [ 8 , 31 ], NiO [ 32 , 33 ], CuO [ 34 ], MnO [ 35 ], MnO 2 [ 36 , 37 ], Mn 3 O 4 [ 27 , 38 ], Nb 2 O 5 [ 28 , 39 ], Fe 2 O 3 [ 40 ], ZrO 2 [ 41 ], WO 3 [ 42 ], and other MOs (In 2 O 3 [ 43 , 44 ], Al 2 O 3 [ 43 ], Sb 2 O 3 [ 6 , 30 ], B 2 O 3 [ 45 ], SiO 2 [ 46 ], etc. ), as well as TiO 2 [ 47 ] and SnO 2 [ 48 ], are used as VEDs.…”