The influence of WO3 on microstructure and electrical characteristics of ZnO-Bi2O3-based varistor ceramics, sintered at 950 oC was studied. The addition of WO3 mainly influences on the type of the Bi2O3-rich phase at the grain boundaries and their electrical characteristics, which we explained based on the results of the impendence spectroscopy analysis. Optimal addition of WO3, which noticeably improved the I-U characteristics of the varistor ceramics at such low sintering temperature was found at 0.4 mol.%, while with higher addition decreased.
COBISS.SI-ID: 28272423
Grain growth and microstructure development in ZnO ceramics with addition of Bi4Ti3O12 (BIT) were studied in dependence of sintering temperature, heating rate and inversion boundary (IBs) nucleation. We found that rapid decomposition of BIT to TiO2-rich Bi2O3 liquid resulted into homogeneous microstructure development with IBS in most of the ZnO grains in accordance to the IB-induced grain growth mechanism. Nucleation of Ti-rich IBs is enhanced by formation of free TiO2 in the presence of ob Bi2O3-liquid, which enables fast diffusion of Ti4+ and can be achieved by immediate exposure of the sample to a temperature above the decomposition temperature of BIT. The results are significant for development of coarse grained Zn-based varisto ceramics with narrow grain size distribution, low breakdown voltage below 50V/mm and good nonlinearity.
COBISS.SI-ID: 26106151
Preparation of transparent conductive ZnO films on glass using method of low temperature hydrothermal synthesis at 90oC from solution of Zn-acetate and Na-citrate was studied. Growth of dense, smooth, highly (0001) oriented polycrystalline ZnO film with optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only few 100Ohm.sq-1, which requires proper nucleation layer on glass, was explained by spatially confined oriented growth (SCOG) mechanism.
COBISS.SI-ID: 25764903
Inversion boundaries (IBs), which are triggered by addition of dopants such as Sb2O3, SnO2 in TiO2 are the most common type of planar faults in ZnO-based ceramics. In the article structural and chemical characteristics of IBa are presented with their key role in grain growth and microstructure development of ZnO-based ceramic, which has important influence on the development of varistor ceramics. An IB-induced grain growth mechanism is discussed, which can be exploited for fine tailoring of current-voltage (I-U) characteristics of varistor ceramics in broad range of breakdown voltages from 60V/mm (coarse grained microstructure) to 350V/mm (fine grained microstructure), all with addition of Sb2O3.
COBISS.SI-ID: 25117735
In the article we report on the ZnO grain-growth kinetics in the ZnO ceramics doped with Bi2O3 and SnO2, in the temperature range between 950oC and 1300oC. Doping with SnO2 results in formation of inversion boundaries (IBs) in ZnO grains, which have key influence on the grain growth. Grains with IBs grow exaggeratedly and anisotroplically in the direction of IBs, causing plate-like development of these grains. At lower sintering temperature the growth is characterized by low grain growth exponent N of 2, from 15 min to 240 mi of sintering. At higher sintering temperatures grain growt under influence of s is finished already after approximately 15 min and the N-value is even lower, about 1.4 at 1300oC. Such low N-values indicate on two-dimensional plate-like grain growth under the influence of IBs. The growth under the influence of IBs is characterized also by low energy for the grain growth of about 148kJ/mol. After the impingement of the plate-like ZnO grains with IBs, the grain is slower and follows Ostwald-ripening mechanism, grain-growth exponent N increases to about 3.5 and grain-growth energy to about 353kJ/mol. After longer sintering time, the sample reach an equilibrium microstructure composed of only ZnO grains with IBs and the grain growth is virtually stopped, which is reflected in very high N-values of 20 and more.
COBISS.SI-ID: 24245799