No abstract

The metastable phase diagram of the Gd2O3–SrO–CoO x system in air was established based on the powder X-ray diffraction results of the 1100 °C-synthesized and then furnace-cooled or slowly-cooled (1 K min−1) samples. It consists of two solid solutions, Gd1−x Sr x CoO3−δ (0.6 ≤ x ≤ 0.9) with a tetragonal I4/mmm superstructure and Gd x Sr2−x CoO4−δ (0.5 ≤ x ≤ 1.2) with a layered tetragonal I4/mmm K2NiF4-type structure, and one ternary compound Gd2SrCo2O7 with a tetragonal P42/mnm structure. The existence of six binary oxide compounds Gd2SrO4, GdCoO3, Sr2Co2O5 (R), Sr6Co5O15, Sr5Co4O12 and Sr14Co11O33 was confirmed. This metastable phase diagram is of technological interest in the controlled preparation of single-phase complex oxides. New phases Gd0.375Sr2.625Co2O7−δ and τ4 with an orthorhombic Immm structure were found in the quenched samples. Differences between the present metastable phase diagram and the reported 1100 °C equilibrium one are discussed.