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The results of a study of the GdAlO3–SrO section, which is one of the internal sections of the Gd2O3–SrO–Al2O3 ternary system, are presented. In the GdAlO3–SrO section three triple compounds, Gd2SrAl2O7, GdSrAlO4, and GdSr2AlO5, crystallizing in the tetragonal system, are synthesized. The data on the mechanism of their solid-phase formation are systematized. The results of the thermal stability of perovskite-like phases in the GdAlO3–SrO system are presented in a wide temperature range of 1100–1800°C in air. The congruent character of the melting of Gd2SrAl2O7, GdSrAlO4, and GdSr2AlO5 complex oxides is established and their melting temperatures are determined. [ABSTRACT FROM AUTHOR]

The combination of technically useful physicochemical properties allows the use of materials based on lutetium aluminates as lasers and scintillators in calorimetry in high energy physics and in medical diagnostics. Synthesis of single crystals based on lutetium aluminates LuAlO3 and Lu3Al5O12 is carried out in inert, inert-reducing media, and in vacuum. In this study, the stability of lutetium aluminates in the Lu2O3–Al2O3 systems is studied for the first time by differential thermal analysis up to 2100°C followed by X-ray phase analysis in a helium atmosphere and dynamic vacuum. A comparative analysis of the behavior of lutetium aluminates with the previously obtained data in air and in an argon-hydrogen atmosphere is carried out. We use single crystals of LuAlO3 (structural type of perovskite) and Lu3Al5O12 (structural type of garnet) obtained by the Bridgman method. Lu4Al2O9 polycrystals (monoclinic structure) are synthesized by melt quenching. [ABSTRACT FROM AUTHOR]

The mechanism of formation of the perovskite-like layered structure of the oxide Gd2SrFe2O7 was studied. The limiting stages are those of formation of phases with perovskite (GdFeO3, SrFeO3− x ) and K2NiF4 (GdSrFeO4) structures. The Mössbauer study has shown that iron atoms exist in a heterovalent state (Fe3+ and Fe4+) only in the structure of SrFeO3− x ). [ABSTRACT FROM AUTHOR]

Phase formation in the Ln2O3-SrO-Al2O3 system (Ln = Nd, Sm) was studied in the range 900-1530°C. Comparative examination of the kinetics of the synthesis of Ln2SrAl2O7 oxides (Ln = La, Nd, Sm) showed that this reaction proceeds by a common mechanism and is substantially faster for neodymium and samarium complex aluminates than for lanthanum aluminate. [ABSTRACT FROM AUTHOR]

Phase formation processes in the systems Ln2O3-SrO-Fe2O3 (Ln = La, Nd) in air in the temperature range 1200–1500°C were studied. The synthesis of the complex ferrites La2SrFe2O7 and Nb2SrFe2O7 involves the formation of the intermediate compounds LnFeO3 and LnSrFeO4 and occurs by the same mechanism as the synthesis of the corresponding aluminates, but much faster. [ABSTRACT FROM AUTHOR]

Phase formation processes in the systems Ln2O3-SrO-Fe2O3 (Ln = La, Nd) in air in the temperature range 1200–1500°C were studied. The synthesis of the complex ferrites La2SrFe2O7 and Nb2SrFe2O7 involves the formation of the intermediate compounds LnFeO3 and LnSrFeO4 and occurs by the same mechanism as the synthesis of the corresponding aluminates, but much faster. [ABSTRACT FROM AUTHOR]

The mechanism of formation of the perovskite-like layered structure of the oxide Gd2SrFe2O7 was studied. The limiting stages are those of formation of phases with perovskite (GdFeO3, SrFeO3− x ) and K2NiF4 (GdSrFeO4) structures. The Mössbauer study has shown that iron atoms exist in a heterovalent state (Fe3+ and Fe4+) only in the structure of SrFeO3− x ). [ABSTRACT FROM AUTHOR]

The series of complex aluminates RE2SrAl2O7 (RE = La, Nd, Sm, Eu, Gd, Tb, Dy, Ho) was prepared at 1450 °C. Their structure is the double perovskite slab–rocksalt layer P2/RS intergrowth of the n=2 Ruddelsden–Popper phases. X-ray Rietveld refinement calculations point to a progressive RE-Sr ordering between the ninefold sites in the RS layers and the twelvefold one in the P2 slabs, respectively. This ordering proves both to improve the ease to prepare these aluminates and stabilize their intergrowth structure. The limit observed for RE=Ho corresponds to a nearly fully ordered distribution of the Ho3+ and Sr2+ cations – 91%. Due to an excess structure-bonding anisotropy in the ninefold sites, a further extent to smaller RE3+ cations is unsuccessful. These results well compare with those regarding the magnetoresistant manganites RE1+xSr2−xMn2O7: increasing RE-Sr ordering and limit found for Er. The big size A element long range ordering phenomena which are unlikely to depend on redox phenomena of the B element in the P2 slabs, have to be considered as specific trends of the P2/RS intergrowth type complex oxides. [Copyright &y& Elsevier]