Kaikan L. S. UkraineIvano-Frankovsk Carpathian National University of V. Stefanik, 57, Shevchenko St., Ivano-Frankovsk, 76025 Author's articles Electrophysical properties of non-stoichiometric lithium-iron magnesium-substituted spinels Dielectric qualities of lithium iron spineless doped by ion Mg+ on basis of impedance temperature researches