**3. Conclusions**

Finely dispersed xerogel nanopowders of the compositions (СeO2)1-x(Sm2O3)x (x = 0.02, 0.05, 0.10), La1-xSrxCo(Ni)O3, and La1-xSrxFe0.7Ni0.3O3 (x = 0.3, 0.4) with an average crystallite size of 8–10 nm are obtained by co-crystallization of salts with ultrasonic treatment. Their consolidation by cold uniaxial pressing at the pressure of 150 or 100 MPa followed by sintering at 900–1300°C provided ceramic electrolyte and cathode materials. At 600–1300°C, the obtained ceramic materials are single-phase solid solutions with a fluorite type cubic structure for the СeO2–Sm2O3 system, perovskitetype tetragonal, and orthorhombic structure for La2О3–SrO–Co(Ni)2О<sup>3</sup> and La2О3–SrO– Fe2O3-Ni2О<sup>3</sup> systems. The obtained ceramic materials are characterized by CSR 64– 81 nm (1300°C), open porosity in the range of 2–30%, and relative density of 97–94%. Materials based on cerium oxide have the conductivity <sup>σ</sup>700°<sup>С</sup> = 1.3<sup>10</sup><sup>2</sup> S/cm of predominantly ionic type ion transfer numbers ti = 0.82–0.71 in the temperature range of 300–700°С, due to the formation of mobile oxygen vacancies during the heterovalent substitution of Ce4+ for Sm3+. Solid solutions based on nickelate and lanthanum cobaltite have mixed electron-ionic conductivity <sup>σ</sup>700°<sup>С</sup> = 0.80<sup>10</sup><sup>1</sup> S/cm with transfer numbers te = 0.98–0.90, ti = 0.02–0.10. Lanthanum nickelate features a higher electrical conductivity compared to lanthanum cobaltite; both solid solutions are characterized by an increase in electrical conductivity with the content of strontium oxide. In addition, ceramics with a perovskite-type tetragonal crystal structure show higher electrical conductivity compared to materials with an orthorhombic perovskite-type crystal structure.

The commensurability of TEC values of the resulting electrolyte material based on cerium dioxide (12.2–12.5<sup>10</sup><sup>6</sup> <sup>K</sup><sup>1</sup> ) and cathode materials based on lanthanum nickelate (12.8–14.2<sup>10</sup><sup>6</sup> <sup>K</sup><sup>1</sup> ) has been established, which makes it possible to consider this pair of ceramic materials as SOFC component.

The obtained ceramics materials according to their mechanical (open porosity, density and thermal expansion coefficient) and electrophysical properties are promising as solid oxide electrolytes and cathodes of medium-temperature fuel cells.
