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The search for new economically advantageous technologies of new zinc oxide based composite ceramic materials and the study of their structure and properties attract special attention today. These ceramics have a number of advantages as compared with materials prepared by more expensive technologies, due to the possibility to fabricate items having different shapes and sizes and particularly to vary their morphology, structure and phase composition. This allows controlling their functional properties by varying the powder particle size in charge, the temperatures, durations and atmospheres of synthesis and heat treatment, and the types of doping impurities in the ceramics. The structure and electrical properties of (FexOy)10(ZnO)90 ceramics (0 ≤ x ≤ 3; 1 ≤ y ≤ 4) synthesized in air using single- and two-stage synthesis methods have been studied. FeO, α-Fe2O3 and Fe3O4 powders or (α-Fe2O3 + FeO) mixture have been used for ZnO doping. X-ray diffraction, gamma-ray resonance spectroscopy and Raman spectroscopy data suggest that at average iron concentrations of 1–3 at.% the ceramic specimens contain at least three phases: the Zn1-δFeδO solid solution with a wurtzite structure, the ZnFe2O4 ferrite phase with a spinel structure and FexOy residual iron oxides which were used as doping impurities. Scanning electron microscopy and energy dispersion X-ray analysis have shown that the wurtzite phase grain size in the ceramic specimens decreases from several decades of microns for single-stage synthesis to submicron sizes for two- stage synthesis. We show that iron addition to ZnO induces a compression of the wurtzite phase crystal lattice, the compression of lattice magnitude being proportional to the oxygen content in the FexOy iron oxide doping agent. The temperature dependences of the electrical resistivity suggest that deep donor centers with an activation energy of about 0.37 eV are formed in the Zn1-δFeδO wurtzite phase. The temperature dependences of the electrical resistivity of electrons for undoped ZnO in the 6–300 K range and for doped (FeO)10(ZnO)90 ceramic synthesized in one stage exhibit a variable activation energy below 50 K which indicates a heavily disordered structure.

Crystal structure formation of BaAl2Si2O8 known as polymorphic compound is investigated in present work depending on conditions of preparation. Characteristics of ceramics have been studied for dierent modications of crystal structure. Additional technologic operations (grinding with following heat treatment) have been found to result in polymorphic transformation. Dielectric properties of BaAl2Si2O8 ceramics have been studied for hexagonal, monoclinic crystal structure modications as well as for that based on phase mixture. It has been shown that the sintering of ceramic material based on the monoclinic crystal structure modication of BaAl2Si2O8 takes place in temperature diapason of 13001350• C. Sintering of material with the hexagonal crystal structure modication occurs in temperature diapason of 14501500• C. Ceramics materials based on compound BaAl2Si2O8 are found to have low porosity, high Q-factor and dielectric characteristics, allowing use of these ceramic materials for production of resonators and other microwave equipments.

This work is focused on the analysis of phase structure and temperature dependences of electric resistivity ρ(Т) in ZnO-based composite ceramics (ZnO) 90 (Fe x O y) 10 , doped with Fe by the addition of 10 wt.% of one of the iron oxides Fe x O y. Streszczenie. Praca koncentruje się na analizie struktury fazowej oraz zależności temperaturowych rezystywności elektrycznej ρ(Т) kompozytów ceramicznych (ZnO) 90 (FexOy) 10 opartych o ZnO, domieszkowanych Fe poprzez dodanie 10% wag. jednego z tlenków żelaza Fe x O y. (Własności elektryczne ceramiki kompozytowej na bazie ZnO domieszkowanej Fe)

In this work, we study the effect of adding iron oxides FeO and Fe2O3 in a ratio of 1 : 9 on the thermal and thermoelectric characteristics of ceramics based on zinc oxide ZnO. The samples themselves were made in two stages based on the ceramic technology of sintering powder mixtures in an open atmosphere. Thermal conductivity studies point to the dominant contribution of lattice thermal conductivity at room temperature. The decrease in thermal conductivity as a result of alloying is due to an increase in phonon scattering at point defects introduced into the ZnO lattice (due to the replacement of zinc ions by iron ions) and at grain boundaries (due to microstructure refinement), as well as an increase in porosity (a decrease in density) and the formation of particles of an additional ZnFe2O4 ferrite phase. Alloying wit iron and the accompanying change in the structure of ceramics (decrease in grain size, increase in porosity, precipitation of the ferrite phase) leads to an increase in the thermoelectric figure of merit ZT by 2 times (due to a decrease in electricalresistivity and thermal conductivity with a relatively small decrease in the thermoelectric coefficient). The results obtained can be used to fabricate ZnO-based ceramics with optimal thermoelectric characteristics.