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
The influence of the ZnO seed layer on the growth of highly oriented ZnO films on glass substrate under low-temperature hydrothermal conditions at 90oC from aqueous solution of Zn-nitrate and Na-citrate was studied. It is shown that continuous ZnO seed-layer with proper thickness, grain size, connectivity, and orientation of seed-grains on glass is essential for the growth of highly (0001) oriented, smooth, transparent, and conductive ZnO films according to the spatially confined oriented growth (SCOG). The film grown on homogeneous seed layer prepared from 0.50M Zn-acetate solution calcined at 350oC with grain size of about 20 nm showed optical transmittance of up to 82% and relatively low resistivity for undoped ZnO ceramics in order of few 100 Ohm.sq-1.
COBISS.SI-ID: 26554407
In this plenary lecture, 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 from 7 to 12 wt.% 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.
COBISS.SI-ID: 27456807