| 1. |
- Andronic, L., et al.
(author)
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Photocatalytic self-cleaning properties of thin films of photochromic yttrium oxyhydride
- 2022
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In: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 316
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Journal article (peer-reviewed)abstract
- Oxyhydride of yttrium (YHO) belongs to an emerging class of materials, with oxide and hydride anions sharingthe same sites in the lattice. Under sunlight irradiation, the material is transparent to visible light with trans-parency exceeding 85% and can absorb about 10% of sunlight. Furthermore, increasing light transmittance in thevisible light enhanced the self-cleaning properties of the coated materials, making these materials promisingcandidates for smart windows applications. However, the light-absorbing properties of the materials wereincreased with exposure time, and in the photodarkening state, they can absorb about 40% of sunlight. Kelvinprobe measurements show work function values between 2.9 and 4.2 eV for YHO, depending on the H2/Arpressure in the deposition chamber. Using the Kelvin probe, we demonstrate that the work function decreaseswith decreasing deposition pressure and hydrogen flow. Measurements under solar light reveal a decrease of workfunction by 0.2 eV followed by a slow relaxation with the light off. Moreover, the self-cleaning test shows that theoxyhydroxide thin films have excellent photocatalytic activity and total self-cleaning in 40 h.
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| 2. |
- B. Brant Carvalho, Paulo H., et al.
(author)
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Elucidating the guest disorder in structure II argon hydrate : A neutron diffraction isotopic substitution study
- 2020
-
In: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 285
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Journal article (peer-reviewed)abstract
- Clathrate hydrates with the cubic structure II (CS-II) form typically with large guest molecules, such as tetrahydrofuran, trimethylamine oxide, or propane. However, CS-II is also realized for argon hydrate despite the comparatively small van der Waals diameter of the guest (around 3.8 angstrom). Here, the structure of deuterated argon hydrate was studied at ambient pressure in the temperature range 20-95 K using neutron diffraction and comparing natural Ar with Ar-36, which scatters neutrons more than 13 times more efficiently. The procedure allowed to unambiguously establish the positional disorder within the large cages of CS-H, while simultaneously refining host and guest structures. These cages are singly occupied and off-centered argon atoms distribute on two tetrahedron-shaped split positions with a ratio 3:1. Molecular dynamics (MD) simulations revealed that the crystallographic positional disorder structure is due to mobile argon atoms even at 20 K. The MD potential energy distribution confirmed the diffraction model. It is noted that the unit cell volumes of argon hydrate in the investigated temperature range are virtually identical to N-2 hydrate, which has a similar composition at ambient pressure, indicating a very similar (slightly attractive) host-guest interaction.
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| 3. |
- Babizhetskyy, Volodymyr, et al.
(author)
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Crystal and electronic structures of the new ternary gallide Zr12Pd40−xGa31+y (x = 0–1.5, y = 0–0.5)
- 2023
-
In: Journal of Solid State Chemistry. - 0022-4596 .- 1095-726X. ; 327
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Journal article (peer-reviewed)abstract
- Zr12Pd40Ga31 was prepared from the elements by arc melting under argon and subsequent annealing at 870 K for 720 h. Single-crystal X-ray diffraction reveals that Zr12Pd40Ga31 crystallizes in a new hexagonal structure type: Pearson symbol (PS) hP166, space group P6/mmm, a = 18.7670(6) Ǻ, c = 8.6634(6) Ǻ). The crystal structure consists of three types of atomic layers – two flat sheets at z = 0 (layer A) and z = 0.5 (C) and one corrugated at z = 0.25 and z = 0.75 (B), which stack in the sequence … ABCB … along the [001] direction. The structure shows close vicinity to a series of hexagonal structures with PS hP164–hP171. These compounds show peculiar structural variability expressed in the different atomic occupations of the Wyckoff positions along and around the 3-fold and 6-fold axes. Homogeneity range and lattice parameters of new ternary compound Zr12Pd40−xGa31+y (x = 0–1.5, y = 0–0.5) have been refined from EDX and powder XRD data. Electronic structure calculations and bonding analysis have been performed for an idealized model revealing domination of the Pd–Ga and Ga–Ga interactions.
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| 4. |
- Cedervall, Johan, et al.
(author)
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Phase stability and structural transitions in compositionally complex LnMO 3 perovskites
- 2021
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 300
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Journal article (peer-reviewed)abstract
- Entropy stabilised materials have possibilities for tailoring functionalities to overcome challenges in materials science. The concept of configurational entropy can also be applied to metal oxides, but it is unclear whether these could be considered as solid solutions in the case of perovskite-structured oxides and if the configurational entropy plays a stabilising role. In this study, compositionally complex perovskite oxides, LnMO3 (Ln = La, Nd, Sm, Ca and Sr, M = Ti, Cr, Mn, Fe, Co, Ni, and Cu), are investigated for their phase stability and magnetic behaviour. Phase-pure samples were synthesised, and the room temperature structures were found to crystallise in either Pnma or R3¯c space groups, depending on the composition and the resulting tolerance factor, while the structural transition temperatures correlate with the pseudo cubic unit cell volume. The techniques used included diffraction with X-rays and neutrons, both ex- and in-situ, X-ray photoelectron spectroscopy, magnetometry as well as electron microscopy. Neutron diffraction studies on one sample reveal that no oxygen vacancies are found in the structure and that the magnetic properties are ferrimagnetic-like with magnetic moments mainly coupled antiferromagnetically along the crystallographic c-direction. X-ray photoelectron spectroscopy gave indications of the oxidation states of the constituting ions where several mixed oxidation states are observed in these valence-compensated perovskites.
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| 5. |
- Clulow, Rebecca, et al.
(author)
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Magnetic and Structural Properties of the Fe5Si1-xGexB2 System
- 2022
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 316
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Journal article (peer-reviewed)abstract
- A series of compounds with compositions Fe5Si1-xGexB2 were synthesised and their structural and magnetic properties were investigated. The Mo5SiB2-type structure with tetragonal I4/mcm space group is maintained for all compounds with x < 0.15, which is estimated as the compositional limit of the system. The unit cell pa-rameters expand with Ge content before reaching a plateau of a = 5.5581(1) and c = 10.3545(1) angstrom at x = 0.15. The saturation magnetisation (MS) decreased slightly with increasing Ge content whilst the magnetocrystalline anisotropy energy (MAE) remains almost unaffected. The Curie temperature for all compounds studied is at 790 K whilst the spin-reorientation temperature shows suppression from 172 K to 101 K where x = 0.15. Ab Initio calculations reveal an increase in MAE for compositions up to x = 0.25 and a decreased magnitude of MAE of-0.14 MJ/m3 for the hypothetical compound Fe5GeB2 relative to the parent compound Fe5SiB2.
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| 6. |
- Garcia-Ben, Javier, et al.
(author)
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Narrowing the tolerance factor limits for hybrid organic-inorganic dicyanamide-perovskites
- 2022
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 316, s. 123635-
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Journal article (peer-reviewed)abstract
- In this work we focus in setting the limits of the tolerance factor and the size of the A-cations that stabilize the perovskite structure in hybrid dicyanamide compounds [A][Mn(dca)3]. For this purpose, we propose an alter-native, simple approach to calculate a more realistic effective ionic radius for the large and anisotropic A-cations often present in these type of compounds. We test the proposed procedure by analysing the crystal structures of [A][Mn(dca)3] dicyanamide hybrids reported in the literature and recalculating the tolerance factors of such compounds, as well as by preparing five new [A][Mn(dca)3] members, discussing also the influence of the A -cation shape in the stability limits of the perovskite structure. Interestingly, such methodology is not only useful to develop new compounds of the emerging family of (multi)functional multi(stimuli)-responsive dicyanamide materials but can also be applied to other hybrid organic-inorganic perovskites and related materials.
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| 7. |
- Ghanta, Sivaprasad, et al.
(author)
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Synthesis, structure, and physical properties of a Y-Au-Ge 1/1 Tsai-type quasicrystal approximant and Y-14(Au,Ge)(51) with the Gd14Ag51 structure type
- 2023
-
In: Journal of Solid State Chemistry. - 0022-4596 .- 1095-726X. ; 327
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Journal article (peer-reviewed)abstract
- Exploration of the Au-Ge rich part of the pseudo-binary section Y-x(Au0.70Ge0.30)(100-x) (3 < x < 18) in the Y-Au-Ge system afforded the intermetallic compounds Y-3(Au0.7054Ge0.2946)(19-x) (x 0.38) and Y-14(Au0.8313Ge0.1687)(51), which are new representatives of the cubic 1/1 Tsai-type approximant crystal (YbCd6 parent type, space group Im (3) over bar) and the hexagonal Gd14Ag51 structure type (space group P6/m), respectively. Y-3(Au0.7054Ge0.2946)(19-x) decomposes peritectically into Y-14(Au, Ge)(51) phase and melt at around 700 degrees C. In this respect the Y-Au-Ge system deviates from the Y-Au-Si system which firstly contains a second type of 1/1 approximant crystal phase with higher Y content, Y-3.25(Au,Si)(18-x) (x approximate to 0.11) and, secondly, adjacent at higher Y composition there is a stoichiometric and ordered tetragonal phase YAu3Si. Y-3(Au,Ge)(19-x) and Y-14(Au,Ge)(51) exhibit bulk superconductivity of conventional type-II BCS type albeit with very low transition temperatures (below 1 K), which is very similar to the corresponding compounds in the Y-Au-Si system.
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| 8. |
- Gordeeva, Alisa, 1994-, et al.
(author)
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Electronic structure characterization of TiO2-II with the α-PbO2 structure by electron-energy-loss-spectroscopy and comparison with anatase, brookite, and rutile
- 2023
-
In: Journal of Solid State Chemistry. - : Academic Press. - 0022-4596 .- 1095-726X. ; 322
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Journal article (peer-reviewed)abstract
- TiO2-II is a high pressure form of titania with a density about 2% larger than that of rutile. In contrast to the common polymorphs anatase, brookite and rutile its electronic structure and optical properties are poorly characterized. Here we report on a comparative electron-energy-loss-spectroscopy (EELS) study for which high resolution valence-loss and core-loss EELS data were acquired from nanocrystalline (<75 nm sized) titania particles with an energy resolution of about 0.2 eV. Electronic structure features revealed from titanium L3,2 and oxygen K electron energy loss near-edge structures show a strong similarity of TiO2-II with both rutile and brookite, which is attributed to similarities in the connectivity of octahedral TiO6 units with neighboring ones. From combined valence-loss EELS and UV-VIS diffuse reflectance spectroscopy data the band gap of TiO2-II was determined to be indirect and with a magnitude of ∼3.18 eV, which is very similar to anatase (indirect, ∼3.2 eV), and distinctly different from rutile (direct, ∼3.05 eV) and brookite (direct, ∼3.45 eV).
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| 9. |
- Khalili, Roya, et al.
(author)
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Local structures of rare earth phosphate minerals by NMR
- 2022
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In: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 311
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Journal article (peer-reviewed)abstract
- 31P solid state NMR studies combined with DFT calculations were conducted over a chosen series of rare earth element phosphates (REEPO4s), selected on the basis of the size and magnetic properties of REEs (La, Sm, Lu and Yb). PXRD analysis revealed the presence of rhabdophane (La, Sm), monazite (La) and xenotime (Lu, Yb) phases of these phosphate compounds. The direct excitation and cross-polarization 31P NMR studies together with calculations confirmed the PXRD results for the abovementioned bulk structures, but also revealed presence of several local phosphorus environments on surfaces. NMR is sensitive to the atomic level local interactions, and we were able to show that the combination of experimental and theoretical NMR methods can provide information unavailable with other methods. Due to the distinct coordination of the water molecules to crystal surfaces with different Miller plane cleavages, we were able to identify from the NMR spectra the surface structures of the studied minerals. This adds to the knowledge of the bulk structures of REE phosphates and provides preliminary data for studies on coordination of various ligands on REE phosphate surfaces. This combination of experimental and computational methods can further be used for studies on surface chemistry, important for applications in catalysis and extraction of REEs from the minerals.
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| 10. |
- Kibbou, Moussa, et al.
(author)
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Probing the electronic, optical and transport properties of halide double perovskites Rb2InSb(Cl,Br)6 for solar cells and thermoelectric applications
- 2022
-
In: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 312
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Journal article (peer-reviewed)abstract
- Halide-based double perovskites have recently been promoted as high-performing semiconductors for photovoltaic and thermoelectricity applications owing to their outstanding efficiency, non-toxicity and ecological stability. In the framework of this research, we have systematically investigated the structural, mechanical, electronic, optical, and thermoelectric properties of Rb2InSb(Cl,Br)6 double halide perovskites. Based on Born stability and tolerance factor criteria, we have found that Rb2InSb(Cl,Br)6 are mechanically and structurally stable. Furthermore, we have performed a comprehensive evaluation of the electronic, optoelectronic, and thermoelectric characteristics. From the electronic band structure results, Rb2InSbCl6 and Rb2InSbBr6 exhibit direct semiconducting band gaps of 1.41 eV and 0.53 eV, respectively. The optical parameters of Rb2InSb(Cl,Br)6 reveal that our active structures have a higher dielectric constant, with maximum absorption in the visible range reaching over 5.68 = 105 cm1 and high optical conductivity (2.19 fs1 for Rb2InSbCl6 and 2.14 fs1 for Rb2InSbCl6). Moreover, the maximum limited spectroscopic efficiency reaches an impressive value of approximately 28.0% for Rb2InSbBr6 and 33.7% for Rb2InSbCl6. The thermoelectric properties were accurately calculated using the BoltzTraP simulation package. The obtained results reveal a significant electrical conductivity, a strong Seebeck coefficient (S 2756 mu VK1 at 300 K), and an average figure of merit close to one for both structures (ZT 1). Our findings suggest the versatility of these materials and could be used for a wide range of applications, including commercial solar cells and thermoelectricity.
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