Ca3Co4O9 (Ca349) compound is very promising p-type oxide thermelectric material. In this work the 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. In contrary to our expectations 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.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 25136167Sintering, grain growth and microstructure development in ZnO based varistor ceramics at temperatures below 1000oC were studied. Starting composition and heat treatment regime were optimized to enhance microstructure development at such low sintering temperatures for varistor ceramics, which are typically sintered at temperatures in the range from 1100oC to 1300oC. The samples had a high density, a uniform distribution of the main Bi2O3-rich secondary phase and an average grain size in the range from 4 to 8 μm. The well-developed microstructure resulted in good current-voltage characteristics of the samples: breakdown voltages VT in the range from 300V/mm to 700V/mm, coefficient of nonlinearity α 25 to 30, and a low leakage current IL below 1μA.
F.10 Improvements to an existing technological process or technology
COBISS.SI-ID: 26137127The influence of ZnO seed layer on the growth of transparent conductive ZnO films on glass substrate under low temperature hydrothermal (HT) conditions at 90oC was analyzed. Preparation of the seed layer was studied. The key characteristics of seed layer (thickness, size, connectivity and orientation of grains),which essentially influence HT growth of ZnO film in accordance to spatially confined oriented growth (SCOG), can be tailored with concentration of Zn-acetate, thickness of Zn-acetate layer on glass, and temperature and time of calcinations. Depending on the characteristics of the ZnO seed layer, either dense, smooth or highly (0001)-oriented ZnO films with high optical transparency above 60% can be obtained or a porous opaque ones.
F.09 Development of a new technological process or technology
COBISS.SI-ID: 25775399