Synthesis, structure and dielectric properties of new ceramics with K2NiF4-type structure

We report the preparation of ceramics on the basis of solid-solutions La1,8Sr0,2Ni0,8Cu0,2O4 with K2NiF4-type structure by new method and systematically study their structure, morphologies, and dielectric properties. Different values of frequency-independent dielectric constants are observed at wide region of frequencies 10-107 Hz in the ceramics prepared before and after thermobaric treatment of the sample. The highest permittivity ε is of order 103 (at ambient temperature) in the frequency range from 1 kHz to 10 MHz after the sample treatment at 1000 оC and P = 4 GPa during 5 min. An obvious change of grain morphology and sufficient change of structural polyhedra anisotropy in La1,8Sr0,2Ni0,8Cu0,2O4 was observed during the thermobaric treatment. Results of the dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and hopping conduction mechanism of small polaron.