• Krztoń-Maziopa, Anna
• Pomjakushina, E. V.
• Svitlyk, V.
• Chernyshov, D.
• Pomjakushin, V. Yu.
• Conder, K.
• Bosak, A.

Abstract

The crystal and magnetic structures of the superconducting iron-based chalcogenides RbyFe2−xSe2 have been studied by means of single-crystal synchrotron x-ray and high-resolution neutron powder diffraction in the temperature range 2–570 K. The ground state of the crystal is an intrinsically phase-separated state with two distinct-by-symmetry phases. The main phase has the iron vacancy ordered ${5} {5}$ superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have ${5} {5}$-type of ordering and has a smaller in-plane lattice constant a and larger tetragonal c-axis and can be well described by assuming the parent average vacancy disordered structure (I4/mmm space group) with the refined stoichiometry Rb0.60(5)(Fe1.10(5)Se)2. The minority phase amounts to 8–10% mass fraction. The unit cell volume of the minority phase is 3.2% smaller than the one of the main phase at T = 2 K and has quite different temperature dependence. The minority phase merges with the main vacancy ordered phase on heating above the phase separation temperature TP = 475 K. The spatial dimensions of the phase domains strongly increase above TP from 1000 to >2500 Å due to the integration of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at a temperature T = 488 K, close to TP, for a long time drastically reduces the amount of the minority phase.

Topics

• impedance spectroscopy
• atomic force microscopy
• iron
• annealing
• space group
• vacancy
• ordered phase