title: Crystal structure of BaFe2Se3 as a function of temperature and pressure: phase transition phenomena and high-order expansion of Landau potential.
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, which 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 the Landau potential. A generic phase diagram mapping observed structures is proposed on the basis of the parameterization.
authors.affiliation: Institut für Anorganische und Analytische Chemie, WWU Münster, Münster, Germany. svitlyk@esrf.fr
authors.forename: V
authors.initials: V
authors.lastname: Svitlyk
authors.forename: D
authors.initials: D
authors.lastname: Chernyshov
authors.forename: E
authors.initials: E
authors.lastname: Pomjakushina
authors.forename: A
authors.initials: A
authors.lastname: Krzton-Maziopa
authors.forename: K
authors.initials: K
authors.lastname: Conder
authors.forename: V
authors.initials: V
authors.lastname: Pomjakushin
authors.forename: R
authors.initials: R
authors.lastname: Pöttgen
authors.forename: V
authors.initials: V
authors.lastname: Dmitriev