Lyudmyla Melnichuk

The structural evolution of 1Ce10ScSZ and 0.5Ce0.5Gd10ScSZ ceramics is investigated as a function of sintering temperature in the range of 1100–1500°C. The ceramics are synthesized from commercial powders with compositions of 1 mol.% CeO ₂ – 10 mol.% Sc ₂ O ₃ – 89 mol.% ZrO ₂ (1Ce10ScSZ) and 0.5 mol.% CeO ₂ – 0.5 mol.% Gd – 10 mol.% Sc ₂ O ₃ – 89 mol.% ZrO ₂ (0.5Ce0.5Gd10ScSZ). X‐ray diffraction confirms that the initial powders possess a single‐phase cubic fluorite structure. After sintering, the 0.5Ce0.5Gd10ScSZ ceramics maintains the cubic phase at all temperatures investigated, indicating high structural stability. In contrast, the 1Ce10ScSZ one sintered at 1100°C contains both cubic and rhombohedral phases. These results demonstrate that the Ce/Gd ratio strongly influences phase stability in scandium‐stabilized zirconia. The rhombohedral phase formation in 1Ce10ScSZ is attributed to increased residual porosity, which promotes lattice relaxation and symmetry lowering at low sintering temperatures. A lower heating rate markedly reduces porosity and suppresses rhombohedral formation, leading to fully cubic ceramics.

The structural and electrical characteristics of (Mg,Zn)O ceramics produced using the solid state reaction at 1100 °C for 3 hours were studied applying X-ray diffraction and IR reflection spectroscopy as well as means of direct current measurements versus MgO content in initial charge (varied from 0 to 100 mol.%). It has been shown that electrical conductivity extracted from the IR reflection spectra corresponds to that of hexagonal phase in a solid solution, while plasmon in cubic phase was not observed. The electron concentration in the hexagonal grains of solid solution prepared with MgO content below 30 mol. % in the charge was found to be close to that of ZnO grains. It shows the tendency to decrease with further growth of the MgO content, which was explained by extraction of zinc interstitials, responsible for ZnO conductivity, from ZnO under formation of the MgZnO cubic phase. The direct current measurements have shown the lower conductivity as compared to the value estimated from IR reflection spectra. This fact along with the superlinearity of current-voltage characteristics has been explained by the presence of intergranular barriers, which does not allow obtaining information on the concentration of free electrons in the grain by this method. The possible nature of intergranular barriers as well as the role of grain boundaries in the DC conductivity of samples has been discussed.

ZnO films were grown on p-type Si substrates by radio-frequency magnetron sputtering of ZnO target in pure argon or mixed argon-oxygen plasma and were investigated using atomic force microscopy, spectroscopic ellipsometry, Fourier-transformed infrared spectroscopy and electrical methods. It was observed that the films grown in argon plasma had large surface roughness which increases with the rise of deposition time. The lateral size of ZnO columns showed similar dependence on deposition parameters as the roughness. Contrary to this, the films produced in argon-oxygen plasma were found to be smoother and denser having thinner ZnO columns. These films also demonstrated an abrupt absorption band-gap edge that is the evidence of better crystalline quality of these films (the lower number of native point and elongated defects). Plasmon-phonon interaction in ZnO films as well as the effect of the plasmon system of Si substrate on this interaction was considered. The theoretical approach used for the fitting of specular infrared reflection spectra allowed determining concentration and mobility of free carriers as well as conductivity of ZnO films. It was found that the films grown in pure argon plasma demonstrated a higher concentration and a smaller mobility of free carriers in the comparison with the corresponding parameters of the films grown in argon-oxygen mixed plasma. The direct resistivity measurements show the essentially higher values compared with the values estimated from IR reflection spectra. The possible reasons of this difference are discussed. The utility of infrared reflection spectroscopy for the non-destructive analysis of electro-physical properties of polycrystalline films was shown.

Optical and electrophysical properties of terbium-doped zinc oxide films have been studied, by using the external reflection IR spectroscopy. The films were deposited onto silicon oxide substrates with the help of the magnetron sputtering method. A theoretical analysis of the reflection spectra of the ZnO/SiO2 structure is carried out in the framework of a multioscillatory model in the spectral interval 50–1500 cm−1 and for the electrical field orientation perpendicular to the c-axis (E⊥C). The method of dispersion analysis is applied to determine the optical and electrical properties of ZnO films, as well as the oscillator strengths and damping coefficients in the ZnO film and the SiO2 substrate. The influences of the phonon and plasmon-phonon subsystems in the ZnO film on the shape of IR reflection spectra registered from the Tb–ZnO/SiO2 structure are elucidated.