In the lecture I presented our research in the field of thermoelectric (TE) oxide ceramics types n and p, where tailoring their structure and microstructure opens numerous challenges for improvement of the TE characteristics. In the case of n-type ZnO doped with In2O3 a series of homologous (ZnO)k•In2O3 phases is formed, having a complex structure, resulting from multiple In-occupied defects. They form a framework for the electron conduction and also result in phonon scattering for reduced thermal conductivity. In the case of p-type TE Ca3Co4O9 (Ca349) compound with complex misfit layered structure, various processing methods like conventional sintering (CS), hot-pressing (HP) and spark plasma sintering (SPS) enable tailoring of microstructure with different porosity and degree of texturing, which strongly affect TE characteristics. The screen-printing technology opens way to inexpensive development and processing of TE generators (TEGs). I presented our research on the preparation and characterization of the screen-printed thick-film TE microgenerators on alumina substrates based on the p-tipa Ca3Co4O9 and the n-type (ZnO)5•In2O3.
B.05 Guest lecturer at an institute/university
COBISS.SI-ID: 28186919The Z-meter based on the “Lagre delta-T method” was successfully developed for the fully automated thermoelectric (TE) characterization of samples up to a temperature of about 650 oC (originally up to 500 oC). From the measured values, obtained simultaneously on a single sample, the Seebeck coefficient, the electrical resistivity and the thermal conductivity, the specimen’s figure of merited Z is dertermined. The measurement process is performed in vacuum of 10-2 to 10-3 Pa on samples with a preferred height of about 10 mm and a diameter of maximum 12 mm and takes about 14 hours. The measurements on the Z-meter of the n-type (ZnO)k•In2O3 ceramics and the p-type Ca3Co4O9 ceramics gave TE values matching reports in the literature, which was also confirmed with measurements of the Fe0,95Co0,05Si2 reference material.
F.35 Other
COBISS.SI-ID: 27103527Zinc oxide (ZnO) has many useful characteristics, which are already exploited in different technologies. Preparation of nano- and micro crystals and structures provides specific properties, which enable novel ZnO-based technologies and applications. Synthesis methods in water media at low temperature have many technological and ecological advantages. The PhD Student in his dissertation studied the influence of solution concentration, pH, temperature, precipitation agent and agent for grain growth control on precipitation and subsequent hydrothermal growth and morphology of crystals, which enabled reproducible preparation of ZnO powders with desired morphology (spheres, rods, plate-like, …) and size. Knowledge on the growth of ZnO enabled also preparation of transparent and conductive layers of ZnO on glass using hydrothermal growth at 90 oC. Such layers of ZnO represent possible replacement for the indium-tin oxide layer (ITO) in technologies of flat panel displays, touch screens, solar cells, LEDs, etc.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 273567232The samples of thermoelectric micro-generators composed of ten in series connected thermocouples, either from the p-type Ca3Co4O9 and the Ag/Pd electrode or the n-type (ZnO)5In2O3 and the Pt electrode were made by screen printing on alumina substrate. Measurements showed that the thick film thermoelectric have similar Seebeck coefficient (156microV/K for p-type and -176microV/K for n-type) as classically prepared bulk samples; the Ca3Co4O9 film has similar also electrical resistivity (13mOhm.cm), which is much higher (720 mOhm.cm) for the (ZnO)5In2O3 due to the high porosity of the film. The Ca3Co4O9-based micro-generator had good power factor of 0,1210-3W/K2m, while it was very low (2,910-8W/K2m) for the (ZnO)5In2O3-based one. Our study defined a promising fabrication method for oxide–based thermoelectric devices and also identifies the main challenges associated with microgenerator fabrication.
F.06 Development of a new product
COBISS.SI-ID: 28003623Sintering, 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: 26137127