| 1. |
- Artini, Cristina, et al.
(författare)
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Roadmap on thermoelectricity
- 2023
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Ingår i: Nanotechnology. - : IOP Publishing Ltd. - 0957-4484 .- 1361-6528. ; 34:29
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Tidskriftsartikel (refereegranskat)abstract
- The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices.
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| 2. |
- Grilli, Davide, et al.
(författare)
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Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z : A Symmetric Mirror Homologous Series in the La–Ni–Si System
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:27, s. 10736-10742
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Tidskriftsartikel (refereegranskat)abstract
- A series of four homologous silicides have been discovered during systematic explorations in the central part of the La–Ni–Si system at 1000 °C. All compounds La12.5Ni28.0Si18.3 (n = 3; a = 28.8686(8), c = 4.0737(2) Å, Z = 3), La22.1Ni39.0Si27.8 (n = 4; a = 20.9340(6), c = 4.1245(2) Å, Z = 1), La32.9Ni49.8Si39.3 (n = 5; a = 24.946(1), c = 4.1471(5) Å, Z = 1), and La44.8Ni66.1Si53.4 (n = 6; a = 28.995(5), c = 4.158(1) Å, Z = 1) crystallize in the hexagonal space group P63/m and can be generalized according to Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z with n = 3–6. Their crystal structures are based on AlB2-type building blocks, fused La-centered Ni6Si6 hexagonal prisms, yielding larger oligomeric equilateral domains with the edge size equal to n. The domains extend along the c axis and show checkered ordering of the cationic and anionic parts, while all their atoms are located on mirror planes. Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z can be considered as a mirror series to the La-rich La(n+1)(n+2)Nin(n–1)+2Sin(n+1), where an exchange of the formal cationic and anionic sites, i.e., La and Si, occurs. The La–Ni–Si system is the first system where two such analogous series have been observed.
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| 3. |
- Pani, Marcella, et al.
(författare)
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Four ternary silicides in the La-Ni-Si system : from polyanionic layers to frameworks
- 2022
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033 .- 1466-8033. ; 24:47, s. 8219-8228
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Tidskriftsartikel (refereegranskat)abstract
- The central part of the La–Ni–Si system has been investigated at 800 °C by means of single crystal X-ray diffraction, microscopy and analytical microprobe techniques. The result led to the identification of four new metal-rich silicides: LaNi2Si (Rm, a = 4.0263(3) Å, c = 15.066(2) Å, Z = 3), La2Ni3Si2 (P21/c, a = 6.8789(7) Å, b = 6.2167(3) Å, c = 12.214(1) Å, β = 90.92(1), Z = 4), La3Ni3Si2 (Pnma, a = 7.501(2) Å, b = 14.316(4) Å, c = 6.149(2) Å, Z = 4), La6Ni7Si4 (Pbcm, a = 6.066(1) Å, b = 7.488(1) Å, c = 29.682(5) Å, Z = 4). LaNi2Si belongs to the SrCu2Ga structure type, which is not represented among silicides, while La2Ni3Si2 crystallizes in its own structure type. Both compounds feature layered polyanionic motifs consisting of Ni and Si, which are separated by La. Instead, La6Ni7Si4 and La3Ni3Si2 are characterized by polyanionic networks. The former compound belongs to the Pr6Ni7Si4 structure type, with only two other representatives (Ce and Nd); the latter has been observed only with Rh and Ir. The two structures reveal close structural relationships having multiple identical slabs. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for LaNi2Si, La2Ni3Si2 and La3Ni3Si2 to gain insights into their structure–bonding relationships. Their band structures suggest a metallic character for all compounds. The overall crystal orbital Hamilton populations are dominated by polar Ni–Si bonds, though homoatomic Ni–Ni and La–Ni(Si) bond contributions are not negligible. The variety of bonding patterns may serve as a logical explanation for the number of discovered compounds in this system as well as for the diversity of the observed structures.
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| 4. |
- Provino, Alessia, et al.
(författare)
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Crystal and Magnetic Structures of the Ternary Ho2Ni0.8Si1.2 and Ho2Ni0.8Ge1.2 Compounds : An Example of Intermetallics Crystallizing with the Zr2Ni1–xP Prototype
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:21, s. 16397-16408
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Tidskriftsartikel (refereegranskat)abstract
- We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure.
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| 5. |
- Provino, Alessia, et al.
(författare)
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Stability, Crystal Chemistry, and Magnetism of U2+xN21-xB6 and Nb3-yNi20+yB6 and the Role of Uranium in the Formation of the Quaternary U2-zNbzNi21B6 and U delta Nb3-delta Ni20B6 Systems
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:22, s. 15045-15059
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the U-Ni-B and Nb-Ni-B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U2Ni21B6 and Nb3-yNi20+yB6 [ternary derivatives of the cubic Cr23C6-type (cF116, Fm3m)] have been studied; the formation of the hypothetical U3Ni20B6 and Nb2Ni21B6 has been disproved. U2Ni21B6 [a = 10.6701(2) angstrom] crystallizes in the ordered W2Cr21C6-type, whereas Nb3-yNi20+yB6 [a = 10.5842(1) angstrom] adopts the Mg3Ni20B6-type. Ni in U2Ni21B6 can be substituted by U, leading to the solid solution U2-xNi21+yB6 (0 <= x <= 0.3); oppositely, Nb in Nb3Ni20B6 is partially replaced by Ni, forming the solution Nb3-yNi20+yB6 (0 <= y <= 0.5), none of them reaching the limit corresponding to the hypothetically ordered U3Ni20B6 and Nb2Ni21B6. These results prompted us to investigate quaternary compounds U2-zNbzNi21B6 and U6Nb3-delta Ni20B6: strong competition in the occupancy of the 4a and 8c sites by U, Nb, and Ni atoms has been observed, with the 4a site occupied by U/Ni atoms only and the 8c site filled by U/Nb atoms only. U2Ni21B6, U2.3Ni20.7B6, and Nb3Ni20B6 are Pauli paramagnets. Interestingly, Nb2.5Ni20.5B6 shows ferromagnetism with T-c approximate to 11 K; the Curie-Weiss fit gives an effective magnetic moment of 2.78 mu(B)/Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 mu(B)/fu (approximate to 0.49 mu(B)/Ni). The magnetic moment of Ni at the 4a site induces a moment in all of the Ni atoms of the whole unit cell (32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U2Ni21B6 and Nb3Ni20B6 is energetically preferred. The various electronic states generating ferromagnetism on Nb2.5Ni20.5B6 and Pauli paramagnetism on U2Ni21B6 and Nb3Ni20B6 have been identified.
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