Suppression of the structural phase transition and lattice softening in slightly underdoped Ba(1-x)K(x)Fe2As2 with electronic phase separation

Abstract

We present x-ray powder diffraction (XRPD) and neutron diffraction measurements on the slightly underdoped iron pnictide superconductor Ba(1-x)K(x)Fe2As2, Tc = 32K. Below the magnetic transition temperature Tm = 70K, both techniques show an additional broadening of the nuclear Bragg peaks, suggesting a weak structural phase transition. However, macroscopically the system does not break its tetragonal symmetry down to 15 K. Instead, XRPD patterns at low temperature reveal an increase of the anisotropic microstrain proportionally in all directions. We associate this effect with the electronic phase separation, previously observed in the same material, and with the effect of lattice softening below the magnetic phase transition. We employ density functional theory to evaluate the distribution of atomic positions in the presence of dopant atoms both in the normal and magnetic states, and to quantify the lattice softening, showing that it can account for a major part of the observed increase of the microstrain.

7 pages, 4 figures

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• Thermodynamic phase diagram and phase competition in BaFe2(As1-xPx)2 studied by thermal expansion
• Emergence of Orbital Nematicity in the Tetragonal Phase of BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Electronic phase separation in iron pnictides
• Phase separation of antiferromagnetic ground states in systems with imperfect nesting
• Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states
• Local lattice distortions vs. structural phase transition in NdFeAsO1-xFx
• Magnetic field effects in electron systems with imperfect nesting
• Magnetic neutron scattering studies on the Fe-based superconductor system Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$
• Disorder correction to the Néel temperature of ruthenium-doped BaFe${}_2$As${}_2$: Theoretical analysis