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The phase relations in the BaO–TiO2−δ system within the concentration range of 14–65 mol% BaO under reducing conditions were investigated using high temperature DTA and X-ray powder diffraction. The stable compounds under these conditions were determined, together with the temperatures of the invariant reactions and the liquidus boundaries. The phase relations in this BaO–TiO2–Ti2O3 system under elevated temperatures and reducing atmospheres are represented in the form of quasi-binary phase diagrams. [Copyright &y& Elsevier]

A new barium polytitanate Ba1.054Ti0.946O2.946 was synthesized by a citrate chemical route. The X-ray powder pattern of this compound was indexed to a hexagonal system, with space group P63/mmc and lattice parameters a=5.722(4) and c=13.996(8) A˚. Prolonged annealing of the Ba1.054Ti0.946O2.946 in air at temperatures above 1150°C leads to a peritectoid decomposition reaction yielding Ba2TiO4 and cubic-BaTiO3, consistent with the known phase diagram. A thermal stability study of this compound demonstrates it to be a stable phase under ambient conditions and metastable under low oxygen partial pressures. [ABSTRACT FROM AUTHOR]

Abstract: High-temperature electrical conductivity measurements, structural data from powder X-ray diffraction and 57Fe Mössbauer spectroscopy were combined to study the interrelationship of oxygen ion transport and p- and n-type transport in Sr2(Fe1− x Ga x )2O5, where , 0.1 and 0.2. Although gallium substitution generally decreases the total ion-electron transport, the transition of the orthorhombic brownmillerite structure to a cubic phase on heating results in the recurrence of the conductivity to the same high level as in the parent ferrite (). The changes of the partial contributions to the total conductivity as a function of x are shown to reflect a complicated interplay of the disordering processes that develop in the oxygen sublattice on heating in response to replacement of iron with gallium. [Copyright &y& Elsevier]