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
We report on the new view on the microstructure development in the ZnO-based varistor ceramics, which is based on the understanding of actual grain-growth controlling mechanism under the influence of inversion boundaries, triggered by Sb2O3 as standard growth-controlling dopant in the fine-grained high voltage varistor ceramics. We demonstrated that exploitation of the IBs induced growth mechanism enables, by sintering at 1200oC for 2 hours, preparation of either coarse or fine grained varistor ceramics with excellent nonlineartity and broad range of break-down voltages from 120V/mm to 350V/mm, in compositions with addition of 3- to 4-times lower amounts of varistor dopants added to ZnO than is nowadays standardly used compositions.
COBISS.SI-ID: 25135655
In the article sol-gel synthesis of ZnO nanoparticles from the Zn-acetate is reported. The process of nanoparticles formation was determined and their self-assembling into larger particles with the same orientation was observed. It was found that further solvothermal treatment results in hexagonal, prismatic ZnO mesocrystals.
COBISS.SI-ID: 25000743