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Clathrate phases with crystal structures exhibiting complex disorder have been the subject of many prior studies. Here we report syntheses, crystal and electronic structure, and chemical bonding analysis of a Li-substituted Ge-based clathrate phase with the refined chemical formula Ba8Li5.0(1)Ge41.0, which is a rare example of ternary clathrate-I where alkali metal atoms substitute framework Ge atoms. Two different synthesis methods to grow single crystals of the new clathrate phase are presented, in addition to the classical approach towards polycrystalline materials by combining pure elements in desired stoichiometric ratios. Structure elucidations for samples from different batches were carried out by single-crystal and powder X-ray diffraction methods. The ternary Ba8Li5.0(1)Ge41.0 phase crystallizes in the cubic type-I clathrate structure (space group no. 223, a 10.80 Å), with the unit cell being substantially larger compared to the binary phase Ba8Ge43 (Ba8□3Ge43, a 10.63 Å). The expansion of the unit cell is the result of the Li atoms filling vacancies and substituting atoms in the Ge framework, with Li and Ge co-occupying one crystallographic (6c) site. As such, the Li atoms are situated in four-fold coordination environment surrounded by equidistant Ge atoms. Analysis of chemical bonding applying the electron density/ electron localizability approach reveals ionic interaction of barium with the Li–Ge framework, while the lithium-germanium bonds are strongly polar covalent.
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This content will become publicly available on January 1, 2027
Imaging the atomic scattering potential in centroidal diffraction of elastic electrons
NThe Fraunhofer diffraction of quantum particles from materials with sharp electron-density edges or symmetric bond structures is ubiquitous. In contrast, diffraction from atoms with a characteristic asymptotically diffused electron distribution is far less intuitive, although known for many years. The current study unravels an unusual diffraction mechanism of elastic electrons from diffused atomic diffractors. Consequently, the fringe pattern converted to the Fourier reciprocal space maps out the effective scattering potential, which is not accessible in direct measurements. This may benefit large-volume and multiscale computational modeling of processes in materials where adopting the complex exact potentials is challenging and expensive. The study employs a relativistic partial-wave analysis with atoms modeled in the Dirac-Fock formalism and performs e-Cd measurements in absolute scale. Analysis for Mg, Ba, and Ra targets demonstrates the universality of the mechanism.ot Available
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- PAR ID:
- 10696618
- Publisher / Repository:
- American Physical Society
- Date Published:
- Journal Name:
- Physical Review A
- Volume:
- 113
- Issue:
- 1
- ISSN:
- 2469-9926
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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