**Abstract**

Finely dispersed (СeO2)1-x(Sm2O3)x (x = 0.02; 0.05; 0.10); La1-xSrxNiO3, La1-xSrxCoO3 and La1-xSrxFe0.7Ni0.3O3 (x = 0.30; 0.40) mesoporous xerogel powders are synthesized by co-crystallization of the corresponding nitrates with ultrasonic processing and used to obtain nanoscale ceramic materials with cubic fluorite-like, orthorhombic, and perovskite-like tetragonal crystal structure, respectively, with CSR 64–81 nm (1300°C). Physicochemical characterization of the obtained ceramics revealed that (СeO2)1-x(Sm2O3)x features with open porosity 2–6%, while for La1-xSrxNiO3, La1-xSrxCoO3, and La1-xSrxFe0.7Ni0.3O3, this value is about 21–29%. Ceria-based materials possess a predominantly ionic conductivity (ion transport numbers *ti* = 0.82–0.71 in the temperature range 300–700°C, <sup>σ</sup>700°<sup>С</sup> = 1.3<sup>10</sup><sup>2</sup> S/cm) determined by the formation of mobile oxygen vacancies upon heterovalent substitution of Sm3+ for Се4+. For solid solutions based on lanthanum nickelate and cobaltite, a mixed electronic-ionic conductivity (σ700°<sup>С</sup> = 0.80<sup>10</sup><sup>1</sup> S/cm) with ion transport numbers (*te* = 0.98–0.90, ti = 0.02–0.10) was obtained. The obtained ceramic materials are shown to be promising as solid oxide electrolytes and electrodes for medium-temperature fuel cells.

**Keywords:** co-crystallization of salts, oxides, finely dispersed powders, fuel cells, nanoceramics, electrolytes, electrode materials
