1063-7850/02/2804- $22.00 © 2002 MAIK “Nauka/Interperiodica” 0308 Technical Physics Letters, Vol. 28, No. 4, 2002, pp. 308–310. Translated from Pis’ma v Zhurnal Tekhnicheskoœ Fiziki, Vol. 28, No. 8, 2002, pp. 1–7. Original Russian Text Copyright © 2002 by Kalanov, Ibragimova. The crystal structure of YBa 2 Cu 3 O 7 – δ (YBCO) ceramics belongs to the class of perovskites. In contrast to the ideal perovskite structure (ABO 3 ), the yttrium cuprate exhibits unsaturated coordination with respect to cations. If all the allowed anionic positions in the lat- tice of a superconducting yttrium–barium ceramics were occupied by oxygen atoms, the structure would correspond to the perovskite composition YBa 2 Cu 3 O 9 = [(Y,Ba)CuO 3 ] 3 . Therefore, there is a theoretical poten- tial possibility of intercalating two additional oxygen atoms into the unit cell of a superconducting yttrium– barium ceramics [1]. For this purpose, it is necessary to deform the initial orthorhombic lattice by applying external factors so that all anionic positions would become equipotential. Such an increase in the lattice symmetry of the initial ceramics is accompanied by a phase transition. Attempts at deforming the initial lattice of the YBa 2 Cu 3 O 7 – δ ceramics (so as to introduce two addi- tional oxygen atoms) by thermal or radiation-thermal methods did not lead to the desired results [2, 3]. How- ever, the lattices of oxide-based materials can be also deformed by mechanical means [4]. In particular, it was reported that a thin film of an yttrium–barium ceramics grown on a magnesium oxide substrate proved to be heterogeneous. The film structure comprised alternat- ing layers of the superconducting 123-phase and a cubic perovskite phase, which was caused by internal stresses related to the lattice mismatch between film and substrate [5]. An analogous heterogeneous compo- sition was obtained for a powdered YBCO ceramic sample treated at room temperature in a vibrating mill for 65 h or longer, which led to straining of the surface layers of ceramic particles [6]. Previously [7], we demonstrated the possibility of obtaining a perovskite phase of the YBCO ceramics by creating thermoelastic stresses in the sample. Thus, from the standpoint of the complete phase diagram of the YBCO system, the question concerning the exist- ence of a homogeneous perovskite phase is still open. In particular, it is unclear how cations are arranged, what is the stoichiometry of anions in the corresponding sublattice, and how the conductivity of the whole system would behave. The purpose of this study was to answer these questions. We report on the synthesis, structural analysis, and study of the electrical properties of a homo- geneous perovskite phase in the YBCO system. The initial materials were powdered oxides Y 2 O 3 , Ba 2 O 3 , and CuO taken in the ratio Y : Ba : Cu = 1 : 2 : 3 so as to obtain an YBa 2 Cu 3 O 7 – δ composition. The ini- tial powders were triturated for a prolonged time (>10 h) in an agate mortar and pressed into pellets (with a diameter of 10 mm and a thickness not exceeding 0.6 mm) under a pressure of 1 GPa. Then the pellets were placed into individual cells made of 0.5-mm nichrome wire and arranged in a furnace so as to exclude touching one another or the inner wall surface. The samples were annealed for 20 min at a temperature of 1173 K and then rapidly heated to a temperature slightly above the melting temperature (T m = 1250– 1323 K). After a short-time (<3 min) exposure at this temperature, the samples were allowed to cool down to room temperature with the furnace. Note that exposure above 3 min at T > T m led to partial surface fusion of the pressed pellets. The structural characteristics of the pel- lets were determined by X-ray diffraction measured on a DRON-UM1 diffractometer using CuKα radiation. The temperature dependence of the resistivity was stud- ied by the conventional four-point-probe technique at a dc current of 1 mA in the temperature interval from 77 to 300 K. Figure 1c shows a typical X-ray diffractogram of the as-sintered YBCO sample measured in the point-by- point scan mode. This diffraction pattern principally differs from that observed for a superconducting 123-phase of the YBCO ceramics. An analysis of the X-ray diffraction reflections showed that the pattern fully conforms to the space group Pm3m. This corre- sponds to a simple cubic cell with the lattice parameter a c = 0.4051 nm. Within the framework of the Pm3m space group, the atomic positions in the unit cell are as follows: 1b positions with the coordinates (1/2, 1/2, 1/2) Synthesis and Study of a Perovskite Phase of Yttrium Barium Metal Oxide Ceramics M. U. Kalanov and E. M. Ibragimova Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Uzbekistan Received September 19, 2001 Abstract—A homogeneous cubic perovskite phase of an yttrium–barium ceramics was obtained by creating thermoelastic stresses in a rapidly heated sample of a certain size. The structural parameters of the new phase were determined, and the electric conductivity was measured. © 2002 MAIK “Nauka/Interperiodica”.