Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Yb 4f-Ta 5d Hybridization and Valence Evolution in Tetragonal Tungsten Bronze Ba(3-x)YbxTa5O15

Daisuke Takegami, Haruki Takei, Masato Yoshimura, Takuro Katsufuji, Takashi Mizokawa

Abstract

Here we investigate the electronic structure of the tetragonal tungsten bronze Ba$_{3-x}$Yb$_x$Ta$_{5}$O$_{15}$ by making use of hard x-ray photoemission spectroscopy. The core level spectroscopy shows that the substitution with Yb ions in the series first occurs on the compact S1 site. For $x\leq1$, Yb is found to be dominantly Yb$^{2+}$ with a small mixing of Yb$^{3+}$, while for $x>1$, a significant increase of Yb$^{3+}$ is found, suggesting not only that site S2 favours Yb$^{3+}$, but also that their presence affects also the valency of the ions in site S1. The valence band spectra shows a relatively deep Yb$^{2+}$ doublet, but at the same time indications of a Ta~$5d$-Yb~$4f$ interaction are found, suggesting the presence of Yb~$4f$ carriers at the Fermi level through this hybridization. Our results thus point towards an exotic form of $d$-$f$ electronic interplay that together with the structural degrees of freedom can result in the unusual trends observed in the physical properties of Ba$_{3-x}$Yb$_x$Ta$_{5}$O$_{15}$.

Yb 4f-Ta 5d Hybridization and Valence Evolution in Tetragonal Tungsten Bronze Ba(3-x)YbxTa5O15

Abstract

Here we investigate the electronic structure of the tetragonal tungsten bronze BaYbTaO by making use of hard x-ray photoemission spectroscopy. The core level spectroscopy shows that the substitution with Yb ions in the series first occurs on the compact S1 site. For , Yb is found to be dominantly Yb with a small mixing of Yb, while for , a significant increase of Yb is found, suggesting not only that site S2 favours Yb, but also that their presence affects also the valency of the ions in site S1. The valence band spectra shows a relatively deep Yb doublet, but at the same time indications of a Ta~-Yb~ interaction are found, suggesting the presence of Yb~ carriers at the Fermi level through this hybridization. Our results thus point towards an exotic form of - electronic interplay that together with the structural degrees of freedom can result in the unusual trends observed in the physical properties of BaYbTaO.

Paper Structure

This paper contains 5 sections, 7 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Discussions
  5. Conclusions

Figures (7)

  • Figure 1: Crystal structure of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$ illustrated with the program VESTA VESTA. The brown octahedra correspond to the TaO$_6$, the red spheres to the O ions and the green and dark green spheres to the two distinct Ba sites S1 and S2.
  • Figure 2: HAXPES wide scan of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$ (a), finer close-up scans below 55 eV (b), and the O 1s core level spectra (c).
  • Figure 3: (a) Ba $5p$ core level HAXPES spectra of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$, together with the calculated Ba $5p$ PDOS in Ba$_3$Ta$_5$O$_{15}$. (b) Ba $4d$ core level HAXPES spectra of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$. The intensity has been normalized to the maximum of the peak labelled S2 in order to allow for a better lineshape comparison.
  • Figure 4: (a) Ta $5p$ and (b) Yb $3d$ core level HAXPES spectra of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$.
  • Figure 5: (a) HAXPES valence band spectra of Ba$_3$Ta$_5$O$_{15}$ (x=0), together with the PDOS from LDA calculations, multiplied by their respective photoionization cross-sections at $h\nu=6.5$ keV and a Gaussian broadening to account for experimental resolution. (b) HAXPES valence band spectra of Ba$_{3-x}$Yb$_x$Ta$_5$O$_{15}$ and (c) a close-up near the Fermi level region
  • ...and 2 more figures