Determination of the local structure of CsBi_4−xPb_xTe₆ (x = 0, 0.5) by X-ray absorption spectroscopy

Abstract

We have studied the local structure and valence electronic unoccupied states of thermoelectric CsBiTe and superconducting CsBiPbTe (T ∼ 3 K) by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements. The Bi-L edge EXAFS reveals wide Bi-Te distance distribution for both compounds indicating complex atomic arrangements in the studied system. The mean square relative displacements (MSRDs) of the Bi-Te bond distances appear largely increased in Pb substituted system due to larger overall local disorder, however, one of the Bi-Te bonds shows a reduced disorder. On the other hand, the Bi-L edge XANES is hardly affected by Pb substitution while the Te-L edge XANES reveals increased density of unoccupied Te 5p states. This suggests that the carriers introduced by the Pb substitution in CsBiPbTe preferentially goes on Te sites. Similarly, the Cs-L edge XANES also shows small changes due to Pb-substitution and reduced local disorder indicated by the reduced width of the Cs-L edge white line. We have also shown that the X-ray photoemission spectroscopy (XPS) measurements on various electronic core levels are in a qualitative agreement with the XANES results. These findings are consistent with carrier doping and a reduced disorder in one direction to be likely factors to drive the thermoelectric CsBiTe into a bulk superconductor by Pb-substitution in CsBiPbTe.

Electronic properties across metal-insulator transition in β -pyrochlore-type CsW2O6 epitaxial films

“…Actually, it is revealed from the Rietveld analysis of powder X-ray and neutron diffractions that the Debye-Waller factor of the Cs atom significantly decreases in comparison to that of W and O atoms in the LT phase [9]. Furthermore, similar anomalous core-level spectra of rattling atoms are reported for cage materials [31][32][33][34], including a rattling superconducting material of Ba24Ge100, where the 12d-site Ba exists inside of the large cage of Ge. The 12d-site Ba 4d core levels split into two components (12d-1 and 12d-2) at 300 K reflecting the rattling motion.…”

Change in the electronic structure of the bismuth chalcogenide superconductor CsBi4−x Pb x Te6 by dissociation of the bismuth dimers

“…On the other hand, CsBi 4−x Pb x Te 6 system without Bi dimer shows the shielding volume fraction of about 100%. Since the EXAFS research reported that the Bi dimer distorts the Bi 4 Te 6 layers [16], destabilized regions could exist at grain boundaries and the CsBi 4 Te 6 system might exhibit filamentary superconductivity.…”

“…Therefore, understanding the correlation between the Bi-dimers and the superconductivity in the CsBi 4−x Pb x Te 6 system via a study of the electronic states would be worthwhile. However, XANES and XPS studies [16] on CsBi 4−x Pb x Te 6 (x = 0 and 0.5) are scarce, and the valence band structure of the ABi 4−x Pb x Te 6 superconductor has not yet been experimentally determined. It is, therefore, crucial to study the experimental valence band of stoichiometric CsBi 4 Te 6 and its evolution with Pb substitution in order to understand the occurrence of bulk superconductivity in CsBi 4−x Pb x Te 6 .…”