Abstract
The distortion of atomic structure around In and Cu dopants in sphalerite ZnS was explored by extended X-ray absorption fine structure (EXAFS) spectroscopy enhanced by reverse Monte Carlo (RMC) simulation (RMC-EXAFS method). These data were complemented with quantum chemical Density Functional Theory (DFT) calculations and theoretical modeling of X-ray absorption near edge spectroscopy (XANES) spectra. The RMC-EXAFS method showed that in the absence of Cu, the In-bearing solid solution is formed via the charge compensation scheme 3Zn2+↔2In3+ + □, where □ is a Zn vacancy. The coordination spheres of In remain undistorted. Formation of the solid solution in the case of (In, Cu)-bearing sphalerites follows the charge compensation scheme 2Zn2+↔Cu+ + In3+. In the solid solution, splitting of the interatomic distances in the 2nd and 3rd coordination spheres of In and Cu is observed. The dopants’ local atomic structure is slightly distorted around In but highly distorted around Cu. The DFT calculations showed that the geometries with close arrangement (clustering) of the impurities—In and Cu atoms, or the In atom and a vacancy—are energetically more favorable than the random distribution of the defects. However, as no heavy In atoms were detected in the 2nd shell of Cu by means of EXAFS, and the 2nd shell of In was only slightly distorted, we conclude that the defects are distributed randomly (or at least, not close to each other). The disagreement of the RMC-EXAFS fittings with the results of the DFT calculations, according to which the closest arrangement of dopants is the most stable configuration, can be explained by the presence of other defects of the sphalerite crystal lattice, which were not considered in the DFT calculations.
Highlights
In our previous works [1,2], we studied the local atomic environment and electronic state of dopants (In, Cu, Ag, Au, Cd) in natural and synthetic ZnS crystals by means of X-ray absorption spectroscopy (XAS)
As no heavy In atoms were detected in the 2nd shell of Cu by means of Extended X-ray absorption fine structure (EXAFS), and the 2nd shell of In was only slightly distorted, we conclude that the defects are distributed randomly
The disagreement of the reverse Monte Carlo (RMC)-EXAFS fittings with the results of the Density Functional Theory (DFT) calculations, according to which the closest arrangement of dopants is the most stable configuration, can be explained by the presence of other defects of the sphalerite crystal lattice, which were not considered in the DFT calculations
Summary
In our previous works [1,2], we studied the local atomic environment and electronic state of dopants (In, Cu, Ag, Au, Cd) in natural and synthetic ZnS crystals by means of X-ray absorption spectroscopy (XAS). Analysis of the X-ray absorption near edge structure (XANES)/Extended X-ray absorption fine structure (EXAFS) spectra revealed that in substitutes for Zn in the structure of Minerals 2020, 10, 841; doi:10.3390/min10100841 www.mdpi.com/journal/minerals. The “formal” oxidation state of in equals to 3+ and does not depend on the presence of other impurities. The difference in the “formal” oxidation states of In3+ and Zn2+ implies the substitution scheme 3Zn2+ ↔2In3+ + , where is a Zn vacancy. Enrichment in In is associated with elevated concentrations of Cu. According to our previous data, in the presence of
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.