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Crystal structure of vyacheslavite, U(PO₄)(OH), solved from natural nanocrystal: a precession electron diffraction tomography (PEDT) study and DFT calculations.

ABSTRACT: The crystal structure of the U(iv)-phosphate mineral vyacheslavite has been solved from precession electron diffraction tomography (PEDT) data from the natural nano-crystal and further refined using density-functional theory (DFT) calculations. Vyacheslavite is orthorhombic, with the space group Cmca, with a ≈ 6.96 Å, b ≈ 9.07 Å and c ≈ 12.27 Å, V ≈ 775 Å³ (obtained from PEDT data at 100 K), Z = 8. Its structure is a complex heteropolyhedral framework consisting of sheets of UO₇(OH) and PO₄ polyhedra, running parallel to (001), interconnected by additional PO₄ polyhedra. There is an (OH) group associated with the U(iv) polyhedron. The question of H₂O presence within the small cavities of the framework has been addressed by the DFT calculations, which have proved that vyacheslavite does not contain any significant amount of H₂O at room temperature.

SUBMITTER: Steciuk G

PROVIDER: S-EPMC9065332 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Crystal structure of vyacheslavite, U(PO4)(OH), solved from natural nanocrystal: a precession electron diffraction tomography (PEDT) study and DFT calculations.

Steciuk Gwladys G Ghazisaeed Seyedayat S Kiefer Boris B Plášil Jakub J

RSC advances 20190624 34

The crystal structure of the U(iv)-phosphate mineral vyacheslavite has been solved from precession electron diffraction tomography (PEDT) data from the natural nano-crystal and further refined using density-functional theory (DFT) calculations. Vyacheslavite is orthorhombic, with the space group Cmca, with a ≈ 6.96 Å, b ≈ 9.07 Å and c ≈ 12.27 Å, V ≈ 775 Å3 (obtained from PEDT data at 100 K), Z = 8. Its structure is a complex heteropolyhedral f ...[more]

PMID: 35519355

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Project description:A sequence of chemical vapor synthesis and thermal annealing in defined gas atmospheres was used to prepare phase-pure anatase TiO2 nanocrystal powders featuring clean surfaces and a narrow particle size distribution with a median particle diameter of 14.5 ± 0.5 nm. Random networks of these nanocrystals were immobilized from aqueous dispersions onto conducting substrates and are introduced as model systems for electronic conductivity studies. Thermal annealing of the immobilized films at 100 °C < T < 450 °C in air was performed to generate particle-particle contacts upon virtual preservation of the structural properties of the nanoparticle films. The distribution of electrochemically active electronic states as well as the dependence of the electronic conductivity on the Fermi level position in the semiconductor films was studied in aqueous electrolytes in situ using electrochemical methods. An exponential distribution of surface states is observed to remain unchanged upon sintering. However, capacitive peaks corresponding to deep electron traps in the nanoparticle films shift positive on the potential scale evidencing an increase of the trapping energy upon progressive thermal annealing. These peaks are attributed to trap states at particle-particle interfaces in the random nanocrystal network (i.e., at grain boundaries). In the potential region, where the capacitive peaks are detected, we observe an exponential conductivity variation by up to 5 orders of magnitude. The potential range featuring the exponential conductivity variation shifts positive by up to 0.15 V when increasing the sintering temperature from 100 to 450 °C. Importantly, all films approach a potential- and sintering-temperature-independent maximum conductivity of ∼10-4 Ω-1·cm-1 at more negative potentials. On the basis of these results we introduce a qualitative model, which highlights the detrimental impact of electron traps located on particle-particle interfaces on the electronic conductivity in random semiconductor nanoparticle networks.

Dataset Information

Crystal structure of vyacheslavite, U(PO₄)(OH), solved from natural nanocrystal: a precession electron diffraction tomography (PEDT) study and DFT calculations.

Publications

Crystal structure of vyacheslavite, U(PO<sub>4</sub>)(OH), solved from natural nanocrystal: a precession electron diffraction tomography (PEDT) study and DFT calculations.

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