Hreb V. Modification of the structure and properties of electronics functional materials based on cobaltites of rare-earth elements

The thesis is devoted to establishing the influence of metals displacement in the cationic positions of perovskite cells on the crystal structure, thermal expansion and spin-spin, magnetic and dielectric-metal transitions temperatures and establishment of the principles of the predicted properties control of potential materials of functional electronics based on cobaltites of rare-earth elements. The thesis solves important scientific tasks, namely: X-ray phase and X-ray structural diffraction analysis of the solid solutions crystal structure of mixed cobaltites R1–xR'xCoO3, cobaltites-chromites RCo0.5Cr0.5O3 and cobaltites-gallates RCo1–xGaxO3 at room temperature was performed; a study of the thermal behaviour of the crystal structure of selected nominal compositions was carried out by in situ high-temperature X-ray synchrotron powder diffraction technique; a comparative analysis were performed for the concentration and temperature dependences of the unit cell parameters, the calculated valence bond lengths, their average values and deformation, tolerance factors, etc.; the regions of phase transition from rhombohedral to the rhombic structure are localized in La1–xRxCoO3 systems; the formation of dimensionally pseudocubic and pseudotetragonal cells in systems contained Pr and Nd were detected; the thermal expansion coefficients are calculated, and the influence of cationic substitution on the observed anomalies of the thermal expansion and temperature of the spin-spin, magnetic and dielectric-metal phase transitions is established; the possibility of predicted control of the potential materials functional properties of the thermoelectricity, gas sensors, catalysts, etc., by isovalent substitution of rare-earth elements and cobalt in solid solutions R1–xR'xCoO3 and RCo1–xMxO3 (M = Cr, Ga) is shown.