Local structural studies of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ using atomic pair distribution function analysis

TL;DR

This study uses atomic pair distribution function analysis to investigate local structural changes in Ba$_{1-x}$K$_x$Fe$_2$As$_2$, revealing anisotropic vibrations and systematic evolution of structural parameters with doping.

Contribution

It provides detailed local structural insights into Ba$_{1-x}$K$_x$Fe$_2$As$_2$ using PDF analysis, highlighting anisotropic vibrations and doping-dependent structural evolution.

Findings

Atomic vibrations are anisotropic with $U_{11} = U_{22} e U_{33}$.

Structural parameters evolve systematically with K doping.

Local structure aligns with long-range diffraction data.

Abstract

Systematic local structural studies of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system are undertaken at room temperature using atomic pair distribution function (PDF) analysis. The local structure of the Ba$_{1-x}$K$_x$Fe$_2$As$_2$ is found to be well described by the long-range structure extracted from the diffraction experiments, but with anisotropic atomic vibrations of the constituent atoms ($U_{11}$ = $U_{22} \ne U_{33}$). The crystal unit cell parameters, the FeAs$_4$ tetrahedral angle and the pnictogen height above the Fe-plane are seen to show systematic evolution with K doping, underlining the importance of the structural changes, in addition to the charge doping, in determining the properties of Ba$_{1-x}$K$_x$Fe$_2$As$_2$.