Influence of Baric and Thermobaric Effects on Dielectric Properties of Complex Oxide Ceramics La1.8Sr0.2Ni0.8Co0.2O4+δ

With a purpose to clarify the reasons for the manifestation of high dielectric permittivity (e) of oxides with K2NiF4-type structure, the influences of pressure (up to 50 GPa) and thermobaric effects (T = 1273 K, P = 2.5 GPa) on the electrical properties of the appropriate La1.8Sr0.2Ni0.8Co0.2O4+delta oxide have been analyzed.Ceramic samples have been synthesized by the "solution combustion" method with diammonium citrate and subsequent sintering of pyrolysis products at 1473 K and thermobaric treatment (TBT). At room temperature, the dielectric constant of thermobarically treated ceramics was found to be an order of magnitude greater than e of sample obtained by sintering. Complex studies of electrical properties in broad ranges of pressure, temperatures and electric field frequencies have shown that the permittivity values of La1.8Sr0.2Ni0.8Co0.2O4+delta ceramics are not only due to external causes determined Maxwell-Wagner effects on grain boundaries and heterogeneity. Internal causes, the main of which are associated with bulk processes of charge polarization and distortion of polyhedra when the structure deviates from ideal, as well as with polarization processes caused by polaron carriers, are discussed. The baric behavior of thermo-electromotive (thermo-emf) force for some number of cycles of increasing and subsequent decreasing pressure makes it possible to use the examined material as a conductive medium capable of operating with controlled thermo-emf values under conditions of pressure change.