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Keywords = waimirite

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13 pages, 6368 KiB  
Article
Chemical Adsorption of HF, HCl, and H2O onto YF3 and Isostructural HoF3 Surfaces by First Principles
by Jennifer Anders, Henrik Wiedenhaupt and Beate Paulus
Crystals 2023, 13(4), 555; https://doi.org/10.3390/cryst13040555 - 23 Mar 2023
Cited by 2 | Viewed by 2315
Abstract
The two elements, yttrium and holmium, form a geochemical twin pair as their cations possess equivalent ratios of charge to radius. However, despite their equal electrostatics, a subtle difference in their fluoride or chloride affinity is known within solutions. In this work, we [...] Read more.
The two elements, yttrium and holmium, form a geochemical twin pair as their cations possess equivalent ratios of charge to radius. However, despite their equal electrostatics, a subtle difference in their fluoride or chloride affinity is known within solutions. In this work, we investigated whether this affinity gap is also present within the solid phase and how it depends on the surface configuration. We modeled adsorptions onto β-YF3 (waimirite) and isostructural β-HoF3 by periodic density functional theory. To draw conclusions on the affinity toward fluoride and chloride vs. water, adsorbates of HF, HCl, or H2O onto any of the four highly abundant surfaces of (010), (100), (011), and (101) were studied. Among others, the conformational landscape was explored by 200 ps of ab initio molecular dynamics. For stoichiometric surfaces of both MF3, we indeed found stronger adsorptions for HF than HCl. All (hkl)·H2O showed slightly stronger adsorption energies for HoF3, while for HF and HCl, the metal preferences varied by the surface. While (100) showed the strongest preference for HoF3, (101) preferred YF3 by the same magnitude. Full article
(This article belongs to the Special Issue First Principles Calculation for Crystalline Materials)
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14 pages, 9818 KiB  
Article
First Principle Surface Analysis of YF3 and Isostructural HoF3
by Jennifer Anders, Niklas Limberg and Beate Paulus
Materials 2022, 15(17), 6048; https://doi.org/10.3390/ma15176048 - 1 Sep 2022
Cited by 5 | Viewed by 2282 | Correction
Abstract
The trifluorides of the two high field strength elements yttrium and holmium are studied by periodic density functional theory. As a lanthanide, holmium also belongs to the group of rare earth elements (REE). Due to their equivalent geochemical behavior, both elements form a [...] Read more.
The trifluorides of the two high field strength elements yttrium and holmium are studied by periodic density functional theory. As a lanthanide, holmium also belongs to the group of rare earth elements (REE). Due to their equivalent geochemical behavior, both elements form a geochemical twin pair and consequently, yttrium is generally associated with the REE as REE+Y. Interestingly, it has been found that DFT/DFT+U describe bulk HoF3 best, when the 4f-electrons are excluded from the valence region. An extensive surface stability analysis of YF3 (PBE) and HoF3 (PBE+Ud/3 eV/4f-in-core) using two-dimensional surface models (slabs) is performed. All seven low-lying Miller indices surfaces are considered with all possible stoichiometric or substoichiometric terminations with a maximal fluorine-deficit of two. This leads to a scope of 24 terminations per compound. The resulting Wulff plots consists of seven surfaces with 5–26% abundance for YF3 and six surfaces with 6–34% for HoF3. The stoichiometric (010) surface is dominating in both compounds. However, subtle differences have been found between these two geochemical twins. Full article
(This article belongs to the Section Materials Chemistry)
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