Phase formation in the (1-y)BiFeO3-yBiScO(3) system under ambient and high pressure


Formation and thermal stability of perovskite phases in the BiFel-yScyO3 system (0 <= y <= 0.70) were studied. When the iron-to-scandium substitution rate does not exceed about 15 at%, the single-phase perovskite ceramics with the rhombohedral R3c symmetry (as that of the parent compound, BiFeO3) can be prepared from the stoichiometric mixture of the respective oxides at ambient pressure. Thermal treatment of the oxide mixtures with a higher content of scandium results in formation of two main phases, namely a BiFeO3-like R3c phase and a cubic (Iota 23) sillenite-type phase based on gamma-Bi2O3. Single-phase perovskite ceramics of the BiFe1-yScyO3 composition were synthesized under high pressure from the thermally treated oxide mixtures. When y is between 0 and 0.25 the high-pressure prepared phase is the rhombohedral R3c with the root 2a(p)x root 2a(p),x2 root 3a(p) superstructure (a(p) similar to 4 angstrom is the pseudocubic perovskite unit-cell parameter). The orthorhombic Pnma phase (root 2a(p)x4a(p)x2 root 2a(p)) was obtained in the range of 0.30 <= y <= 0.60, while the monoclinic C2/c phase (root 6a(p)x root 2a(p)x root 6a(p)) is formed when y=0.70. The normalized unit-cell volume drops at the crossover from the rhombohedral to the orthorhombic composition range. The perovskite BiFe1-yScyO3 phases prepared under high pressure are metastable regardless of their symmetry. At ambient pressure, the phases with the compositions in the ranges of 0.20 <= y <= 0.25, 0.30 <= y < 0.50 and 0.50 <= y <= 0.70 start to decompose above 970, 920 and 870 K, respectively.



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Salak, AN; Khalyavin, DD; Pushkarev, AV; Radyush, YV; Olekhnovich, NM; Shilin, AD; Rubanik, VV

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This work was supported by project TUMOCS. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 645660. Financial support of the Belarusian Republican Foundation for Fundamental Research (Project No T15VT-008) is gratefully acknowledged as well. The authors thank Mr. M. Starykevich for help with the SEM study.

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