Intrinsic crystal phase separation in antiferromagnetic superconductor RbyFe2-xSe2: a diffraction study

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 \surd5x\surd5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have \surd5x\surd5-type of ordering and has smaller in plane lattice constant a and larger tetragonal c-axis and can be well described 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 transforms to the main vacancy ordered phase on heating above the phase separation temperature T_P = 475 K. The spatial dimensions of the phase domains strongly increase above TP from 1000 Å to > 2500 Å due to the merging of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at the temperature T=488 K close to T_P for the long time drastically reduces the amount of the minority phase.

added additional figure and section on high T annealing

References in corpus (7)

• Superconductivity at 38 K in the iron arsenide (Ba1-xKx)Fe2As2
• Fe-based high temperature superconductivity with Tc=31K bordering an insulating antiferromagnet in (Tl,K)FexSe2 Crystals
• Superconductivity at 32 K in single crystal Rb${}_{0.78}$Fe${}_2$Se${}_{1.78}$}
• Intrinsic phase separation in superconducting K0.8Fe1.6Se2 (Tc= 31.8 K) single crystals
• Iron vacancy superstructure and possible room temperature antiferromagnetic order in superconducting Cs_{y}Fe_{2-x}Se_2
• Cation vacancy order in the K0.8+xFe1.6-ySe2 system: five-fold cell expansion accommodates 20% tetrahedral vacancies
• Room temperature antiferromagnetic order in superconducting X_yFe_{2-x}Se_ 2, (X= Rb, K): a powder neutron diffraction study

Cited by in corpus (3)

• Phase relations in K_xFe_{2-y}Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction
• Evolution of precipitate morphology during heat treatment and its implications for the superconductivity in KxFe1.6+ySe2 single crystals
• Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation