The dissertation work in Devoted to Synthesis and investigations of physicochemical Properties of Complex Oxide Compounds (COC) based on rare-earth Elements (REE) and Transition metals of perovskite structure and similar to in.
The effect of phase formation and oxygen non-stoichiometry on conductive Properties of Ruddlesden-Popper phase (RPP) has been investigations first for the systems of La-Ni-O, Pr-Ni-O i Nd-Ni-O in the field of low temperatures (300-78 К). The optimal conditions for Synthesis of the phase has been found, their physicochemical Properties were researched. It has shown that high conductivity of the La-Ni-O is due to Ni3+ ions.
The influence of heterovalent isomorphous substitution in such RPP has for the first time La3-xМxNi2O7-δ and La4-xМxNi3O10-δ (М = Ca, Sr, Ba) in a wide substitution interval (0≤x≤2,0) has been studied. As shown, heterovalent isomorphous substitution is limited by the substitute size. The longest regions of Solid solutions are attributed for calcium-containing Solid solutions, the shortest regions are characteristic for barium-containing ones. Doping of alkaline earth metals of all the systems up to a certain limit leads to loss of metallic conductivity and transition of COC to semiconductive state accompanied by decrease of RPP lamination.
In order to search new catalytically active perovskite-based COC, isomorphically substituted systems based on lanthanum cobaltate with alkaline and alkaline-earth Elements were investigated: М’M”CoO3-δ (M’=Sr, La; M”=Li, Na, K), La1-3хLiхМ2хCoO3-δ (М = Са, Sr, Ва; 0≤x≤0,33), La1-2хLiхМхCoO3-δ (М = Са, Sr, Ва; 0≤x≤0,5); nikelates of alkaline and alkaline-earth metals M’M”NiO3-δ (M’=Sr, Ba, La; M”=Li, Na, K) and manganates of alkaline and alkaline-earth metals SrM’MnO3-x (M’=Li, Na, K). It has been shown that selectivity of strontium manganates, nickelates and cobaltate doped with alkaline metals reaches more than 95% for the reactions of methane oxidation. Solid solutions based on lanthanum cobaltate doped with lithium and alkaline-earth metals demonstrate high catalytic activity in reactions of oxidation of carbon monoxide. The temperature of 100% СО conversion has been established to decrease with increase of average ion radius of alkaline-earth metal.
In order to search new conductive and superconductive compounds, REE cuprate and new high temperature superconductors (HTSС) were synthesized and studied. BaCuO2.25 has been synthesized first using secondary induction heating, its structure has been specified, dielectric properties were investigated within the temperature interval of 453-593 К. It was shown that this compound is a semiconductor with thermoactivated type of conductivity, the energy activation of which is 0,2 eV.
The effect of synthesis method on oxygen non-stoichiometry and physicochemical properties of a new representative of HTSC cuprates, namely Y-358 (Y3Ba5Cu8O18+δ), was investigated. In order to establish the effect of isomorphous substitution on structure and superconductive properties of Y-358, the systems with substitution in a sublattice of yttrium and barium were investigated. The homogeneity region of the Y3-xCsxBa5Cu8O18+δ system is 0≤х≤0,1, the superconductivity temperature is Tc = 92-93 K. It is interesting that the substitution causes no sufficient change of superconductivity characteristics. For the Y3Ba5-xSrxCu8O18+δ systems, the homogeneity field of solid solutions is within the interval of 0≤x≤0,2, all the obtained compounds are superconductive with a very narrow wideness of superconductive transition at Tc = 79-82 К depending of the substitute concentration.
Protection of HTSС compounds against degradation in environment is actual problem. In order to solve it, composite materials based on HTSС ceramics, such as YВa2Cu3O6,91 (Y-123) and Bi2Sr2CaCu2O8,2 (Bi-2212) containing inorganic (Al2O3, ZrO2, Nb2O5 аnd Ta2O5) and polymer (polyethylene glycol dimethacrylate) additives. According to their stabilizing effect, the inorganic alloying additives are in the row: ZrO2 ≤ Al2O3 ≈ Ta2O5 ≤ Nb2O5 (for Y-123); and ZrO2<Ta2O5<Nb2O5< Al2O3 (for Bi-2212). Polymer-ceramic composite materials can be divided to two types. The first one are individual granules of the superconductive ceramics are in the polymer matrix (0-3 composites). The second type are three dimension phases of superconductive and polymer components (3-3 composites of polyethylene glycol dimethacrylate) with Y-123 аnd Bi-2212. Degradation of the composites affected by humidity and water vapor has been investigated, the composites are stable under these conditions. As found, two types polymer-composite materials show improvement of mechanical properties: the material is easy to shape. 3-3 composites save their resistive and magnetic properties as opposed to 0-3 composites.
