Calculated effects of disorder on the Mo core levels in purple bronze Li$_2$Mo$_{12}$O$_{34}$

TL;DR

This study uses ab-initio calculations to show that thermal disorder significantly broadens Mo 3d-core levels in Li$_2$Mo$_{12}$O$_{34}$, suggesting core level spectroscopy can detect thermal effects in materials.

Contribution

It demonstrates the impact of thermal and static disorder on core level broadening in purple bronze using first-principles calculations, highlighting potential experimental applications.

Findings

Thermal disorder causes substantial broadening of Mo 3d-core levels.

Room temperature broadening exceeds zero-temperature broadening, enabling detection.

Static disorder from Li vacancies reduces temperature-dependent broadening effects.

Abstract

The band structures of ordered and thermally disordered Li$_2$Mo$_{12}$O$_{34}$ are calculated by use of ab-initio DFT-LMTO method with focus on the behavior of the Mo 3d-core levels. It is shown that thermal disorder and zero-point motion lead to substantial core level broadening, and the broadening at room temperature is predicted to be sufficiently larger than at zero degrees to allow for a detection by XPS measurements. However, real purple bronze has 10 percent of Li vacancies and static disorder will attenuate the $T$-dependent broadening. It is argued that core level spectroscopies could be a useful tool for measuring of thermal disorders in many materials, especially for those with minor static disorder. Studies of core levels in magnetic materials will be helpful for an understanding of $T$-dependent spin moments.