Ceramic system based on ZnO·CuO obtained by freeze-drying

Electric force microscopy investigations of barrier formations in ZnO-based varistors

“…It was also observed that the grain geometry and diameter differ considerably (1-3 m). The grain size can be controlled by sintering temperature and time and also by different additives, as reported by Bellini et al 24,[29][30][31] These images indicate that densification was not complete due to the presence of pores (Fig. 4a).…”

“…In varistors, the leakage current decreases as the grain size decreases, although doped ZnO varistors of small size have a large leakage current. 24,[29][30][31] The EFM images of the ZnO-CuO, ZnO-CuO-G 1 , and ZnOCuO-G 5 varistors depicted in Figs. 4(b, c), 5(b, c), and 6(b, c), respectively, were obtained with a dc bias voltage ranging from 4 and 8 V. These images indicate that increasing the bias tip voltage causes the concentration of negative charges stored in the grain boundary region to increase.…”

The Influences of CuO/ZnO Ratios on the Crystallization Characteristics Electrical and Magnetic Properties of CuxZn1−xO Powders

“…The TGA data reveals a sharp weight loss in the powder at 270 ∘ C because of the evaporation of water and organics [16]. This result is consistent with the DSC curve, which shows an exothermic peak at 280 ∘ C. An endothermic peak appears at 480 ∘ C and the powder weight (TGA curve) gradually increases and then stabilizes as the temperature exceeds 500 ∘ C. The main reason is that the CuO crystallization gradually forms with increasing temperature [17]. Based on these reasons, the CuO powder was annealed at 500 ∘ C to estimate the CuO crystallization.…”

An AFM/EFM Study of the Grain Boundary in ZnO‐Based Varistor Materials

“…The nonlinear coefficient α is considered the quality factor of a varistor, and is defined by the empirical equation I = kV α , where I is the current flowing through the sample, V is the voltage across the sample, k is a constant value of ZCF 1 and ZCF 5 samples, which are 2.73 × 10 −32 mA·(V·m) −1 and 7.93 × 10 −27 mA·(V·m) −1 respectively, and α is the nonohmic exponent. For the sake of comparison, the nonlinear coefficient α can be estimated by the equation α=1/log ( E 5 / V 1 ) using two electric field values, E 5 and E 1 , at 5 and 1 mA/cm 2 settings of the current density, respectively 36 …”

“…29 These authors showed that the presence of CuO in ZnO varistors conferred to the ZnO-CuO varistors the same properties as those that have several dopings such as those proposed by Matsuoka and colleagues 12,20 However, Lee and Tseng [30][31][32][33] showed that due to the poor sinterability of this system and in an attempt to densify the material (CuO doped ZnO), the frit used had the following composition: 26 wt% SiO 2 , 62 wt% PbO, 7 wt% B 2 O 3 , and 5 wt% ZnO. Previous studies on ZnO-CuO-frit varistor systems have been reported by Bellini et al [34][35][36][37] They showed that the addition of a large percentage of frit (5%) led to a low breakdown electric field and a low leakage current.…”