Many complex oxides of transition metals show effect of enormous dielectric permeability. New complex layered oxides LnSr2CuTiO6,5 (Ln = La, Nd, Pr) are synthesized. Their structure by means of x-ray diffraction on the Shimadzu XRD-7000 S is investigated. Processing of XRD was carried out in the program FULLPROF-2013. The main X-ray reflexes are indicated in space group I4/mmm (№ 139). The data of the crystal-chemical analysis which are carried out taking into account a charge state and coordination environment of cations show that distortion of coordination polyhedrons is significantly reduced in series Ln = La→Nd. The unit cell parameters naturally decrease according to reduction of ionic radiuses of La→Nd. Dielectric properties of materials investigated using the universal analyzer of a frequency response Solartron 1260A in the range of frequencies 1mHz - 16МHz with a signal amplitude 500-900 mV. Increasing the dielectric constant is possible due to the charge ordering caused by uneven distribution of charge. Frequency dependences of an imaginary and real part of dielectric constant are given.

Keywords: dielectric constant , complex oxide, transition metal, perovskite, x-ray diffraction, microstructure, crystal-chemical analysis, impedance- spectroscopy, charge ordering, coordination polyhedron

Ceramic materials based on solid solutions La2-xSrxMO4, where M is Ni, Fe, Co, Cu, x = 0, 2 with layered K2NiF4 structure (structure of Ruddlesden-Popper) have been synthesized and investigated. The correlation of dielectric properties with a normalized bond lengths of the metal-oxygen has been observed. The existence of nickel atoms in the 2+ oxidation state for nickelates has been shown.

Keywords: solid solutions, colossal dielectric constant, resistivity, x-ray diffraction, dielectric spectrum, XANES, low-resistivity semiconductors, the activation energy, the distortion of the coordination polyhedra, oxygen non-stoichiometry