The temperature dependences of unit cell parameters of the Nd2-xCexCuO4 +/-y(x = 0, 0.15)T' phase heated from room temperature to 1050 degreesC in a helium atmosphere were obtained by high-temperature X-ray powder diffraction. A possible mechanism of exchange between different oxygen positions of the T'-phase structure at the ultimate stage of forming the Nd1.85Ce0.15CoO4-y HTSC phase is discussed in terms of the known concepts of the influence of intrastructural oxygen disordering on the character of these dependences.

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A retrospective critical analysis of phase diagrams of the CoMnO system in air has been made. A high-temperature phase equilibrium of the CoMnO system in air and phase diagrams of this system under different cooling conditions (quenching in water, quenching in air, cooling at rate of 25°K h−1) have been constructed. A comparative analysis of these diagrams shows that whatever the cooling rate, cooling does not preserve the high-temperature state of the system and is accompanied (depending on cooling conditions, temperature and Co/Mn ratio) by one or more of the following phenomena: (1) oxidation of the CoNMn1−NO solution to spinel-type solid solutions (2) merging of a cubic and tetragonal spinel phase and formation of a homogeneous tetragonally distorted spinel (3) tetragonal distortion of the spinel lattice (4) decomposition of the cubic spinel into a cubic and tetragonal spinel. (5) decomposition of the cubic spinel into a cubic, tetragonal and slightly distorted tetragonal spinel. Therefore, the form of the phase diagram of the CoMnO system in air is entirely determined by the method of cooling.

The purpose of this paper is a study of the dielectric properties of MgMn/sub 2-x/V/sub x/O/sub 4/ at superhigh frequencies in the concentration region where the tetragonal ..-->.. cu. phase transition occurs.