Nanoscale phase separation in the iron chalcogenide superconductor K0.8Fe1.6Se2 as seen via scanning nanofocused x-ray diffraction

TL;DR

This study uses advanced nanofocused X-ray diffraction to visualize and analyze intrinsic nanoscale phase separation in K0.8Fe1.6Se2 superconductors, revealing complex magnetic and non-magnetic domain structures.

Contribution

It provides the first direct visualization of nanoscale phase separation in K0.8Fe1.6Se2 using scanning nanofocus X-ray diffraction, highlighting the spatial distribution of coexisting phases.

Findings

Nanoscale phase separation occurs below 520 K.

Magnetic and non-magnetic phases coexist with distinct lattice structures.

Phase domains are smaller than 300 nm and form a complex network.

Abstract

Advanced synchrotron radiation focusing down to a size of 300 nm has been used to visualize nanoscale phase separation in the K0.8Fe1.6Se2 superconducting system using scanning nanofocus single-crystal X-ray diffraction. The results show an intrinsic phase separation in K0.8Fe1.6Se2 single crystals at T< 520 K, revealing coexistence of i) a magnetic phase characterized by an expanded lattice with superstructures due to Fe vacancy ordering and ii) a non-magnetic phase with an in-plane compressed lattice. The spatial distribution of the two phases at 300 K shows a frustrated or arrested nature of the phase separation. The space-resolved imaging of the phase separation permitted us to provide a direct evidence of nanophase domains smaller than 300 nm and different micrometer-sized regions with percolating magnetic or nonmagnetic domains forming a multiscale complex network of the two phases.