In this invited talk, the classical understanding, explaining microstructure development in the varistor ceramics by the influence of the amount of secondary phases at the grain boundaries of ZnO, which dictate high additions of varistor dopants to ZnO since the discovery of varistor ceramics, was presented at first. Afterwards it was shown that actual mechanism that controls microstructure development is dictated by the grain-growth mechanism under the influence of inversion boundaries (IBs) and IBs are triggered in ZnO grains by very low amounts of Sb2O3. We demonstrated that such understanding enabled us to make varistor ceramics, at addition of only 3 wt.% of varistor dopants to ZnO, with either coarse- or fine-grained microstructure, breakdown voltage ranging from 60V/mm to 350V/mm, and high coefficient of nonlinearity between 30 and 50.
B.04 Guest lecture
COBISS.SI-ID: 24556071This paper of invited talk represents review of our fundamental discoveries abour special boundaries such as inversion boundaries which play the key role in crystal growth of some semiconductive oxide materials. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of semiconducting materials. These effects have important implications and can be exploited for tailoring the electronic and optical properties of the materials, which we demonstrated on examples of the ZnO ceramics and varistor ceramics.
B.04 Guest lecture
COBISS.SI-ID: 25306151The synthesis of p-type thermoelectric Ca3Co4O9 (Ca349) compound is reported. The formation of the Ca349 compound is compared in the cases of classical approach from stoichiometric mixture of CaCO3 - Co3O4 and when the mixture is mechano-chemically activated using high-energy milling. It showed that mechano-chemical treatment resulted only in amorphisation of the powder mixture without any formation of then Ca349 compound or enhancement of its formation. In both cases the Ca349 phase was formed after sintering at 760oC while traces of the Co3O4 were still present.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 25136167