Abstract
The band structures of ordered and thermally disordered Li 2 Mo 12 O 34 are calculated by use of ab initio density functional theory (DFT)–Linear Muffin-Tin Method (LMTO) with a 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 X-ray photoelectron spectroscopy (XPS) measurements. However, real purple bronze has 10% Li vacancies, and static disorder will attenuate the T-dependent broadening. It is argued that core level spectroscopies could be a useful tool for the measurement 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.
Highlights
Lithium Purple Bronze (Li0.9Mo6O17) is an unusual material which has drawn the attention of researchers for nearly three decades [1,2]
The band dispersion along the conducting Γ − Y direction agrees well with the measured results obtained by Angle-resolved photoemission spectroscopy (ARPES) [34], showing a flattening of the two dispersive bands at about 0.4–0.5 eV below EF
The spread in core levels ∆ zero-point motion (ZPM) and ∆ room temperature (RT) in Table 1 is based on the variations of core levels on the different sites among the four disordered “ZPM” and five “RT” configurations, respectively
Summary
Lithium Purple Bronze (Li0.9Mo6O17) is an unusual material which has drawn the attention of researchers for nearly three decades [1,2]. It is a compound with a rather complicated layered structure [3], and it exhibits highly 1-dimensional (1D) electronic properties [4,5,6]. The present work shows that core level broadening from thermal disorder can be large, and it is important to recognize core level spectroscopy as a useful tool for the determination of the effects of disorder on valence states and material properties
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