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arXiv · 1301.0509

Crystal Structure of BaFe2Se3 as a Function of Temperature and Pressure: Phase Transition Phenomena and High-Order Expansion of Landau Potential

V. Svitlyk·D. Chernyshov·E. Pomjakushina·A. Krzton-Maziopa·K. Conder·V. Pomjakushin·R. Pottgen·V. Dmitriev
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Abstract

BaFe2Se3 (Pnma, CsAg2I3-type structure), recently assumed to show superconductivity at ~ 11 K, exhibits a pressure-dependent structural transition to the CsCu2Cl3-type structure (Cmcm space group) around 60 kbar, as evidenced from pressure-dependent synchrotron powder diffraction data. Temperature-dependent synchrotron powder diffraction data indicate an evolution of the room-temperature BaFe2Se3 structure towards a high symmetry CsCu2Cl3 form upon heating. Around 425 K BaFe2Se3 undergoes a reversible, first order isostructural transition, that is supported by the differential scanning calorimetry data. The temperature-dependent structural changes occur in two stages, as determined by the alignment of the FeSe4 tetrahedra and corresponding adjustments of the positions of Ba atoms. On further heating, a second order phase transformation into the Cmcm structure is observed at 660 K. A rather unusual combination of isostructural and second-order phase transformations is parameterized within phenomenological theory assuming high-order expansion of Landau potential. A generic phase diagram mapping observed structures is proposed on the basis of the parameterization.

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V. Svitlyk, D. Chernyshov, E. Pomjakushina, A. Krzton-Maziopa, K. Conder, V. Pomjakushin, R. Pottgen, V. Dmitriev. 2013-01-03. Crystal Structure of BaFe2Se3 as a Function of Temperature and Pressure: Phase Transition Phenomena and High-Order Expansion of Landau Potential. https://doi.org/10.1088/0953-8984%2F25%2F31%2F315403

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