Nanoalloys (NAs) have extraordinary catalytic properties, but metals are often immiscible giving compositional limits on catalytic design. It is generally believed that solution‐based chemical ...synthesis is inadequate for obtaining NAs, and often exotic shock synthesis or severe decomposition or reduction reactions are required. However, such methods only work on the laboratory scale making real‐world applications difficult. Here, a general solvothermal method is reported to obtain phase‐pure bimetallic and high‐entropy nano‐alloys across the entire composition range. Tuning of solvent chemistry and precursors leads to six different bimetallic NAs: PdxRu1‐x, PtxRu1‐x, IrxRu1‐x, RhxRu1‐x, Ir1‐xPtx, and Rh1‐xPtx, without immiscibility regions. All samples have face‐centered‐cubic crystal structures, which have not previously been observed for the ruthenium‐based systems. Additionally, quaternary and quinary systems are produced, demonstrating the ability to obtain medium‐ and high‐entropy NAs. The method described herein provides a simple, general production method of previously unknown solid solutions throughout their entire composition range potentially allowing for detailed tuning of nanocatalyst properties.
Bimetallic nanoparticles have outstanding catalytic properties, but large‐scale synthesis is challenging. Here, a simple solution‐based chemical synthesis method provides a range of phase‐pure bimetallic nanoalloys across the complete composition range allowing for tuning of their properties. Surprisingly, it is even possible to make high‐entropy alloys containing four or five metals.
Abstract
Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited ...either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg
3
Sb
1.5
Bi
0.5
, that exhibits a very high figure of merit
zT
ranging from 0.56 to 1.65 at 300−725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg
3
Sb
1.5
Bi
0.5
a promising candidate for the low- and intermediate-temperature thermoelectric applications.
n‐type Mg3Sb2‐based compounds have emerged as a promising class of low‐cost thermoelectric materials due to their extraordinary performance at low and intermediate temperatures. However, so far, high ...thermoelectric performance has merely been reported in n‐type Mg3Sb2‐Mg3Bi2 alloys with a large amount of Bi. Moreover, current synthesis methods of n‐type Mg3Sb2 bulk thermoelectrics involve multi‐step processes that are time‐ and energy‐consuming. Herein, we report a fast and straightforward approach to fabricate n‐type Mg3Sb2 thermoelectrics using spark plasma sintering, which combines the synthesis and compaction in one step. Using this method, we achieve a high thermoelectric figure of merit zT of about 0.4–1.5 at 300–725 K in n‐type (Sc, Te)‐co‐doped Mg3Sb2 without alloying with Mg3Bi2. In comparison with the currently reported synthesis methods, the complexity, process time, and cost of our method are significantly reduced. This work demonstrates a simple, low‐cost route for the potential large‐scale production of n‐type Mg3Sb2 thermoelectrics.
A simple one‐step approach is developed for preparing high‐performance low‐cost n‐type (Sc, Te)‐doped Mg3Sb2 thermoelectric materials that show a high optimal thermoelectric figure of merit zT of about 1.5 and a high average zT of about 0.9 at 300–725 K. The approach provides a new avenue for the rapid, low‐cost, and large‐scale production of n‐type Mg3Sb2 thermoelectrics.
Abstract The Mg 3 Sb 2 structure is currently being intensely scrutinized due to its outstanding thermoelectric properties. Usually, it is described as a layered Zintl phase with a clear distinction ...between covalent Mg 2 Sb 2 2− layers and ionic Mg 2+ layers. Based on the quantitative chemical bonding analysis, we unravel instead that Mg 3 Sb 2 exhibits a nearly isotropic three-dimensional bonding network with the interlayer and intralayer bonds being mostly ionic and surprisingly similar, which results in the nearly isotropic structural and thermal properties. The isotropic three-dimensional bonding network is found to be broadly applicable to many Mg-containing compounds with the CaAl 2 Si 2 -type structure. Intriguingly, a parameter based on the electron density can be used as an indicator measuring the anisotropy of lattice thermal conductivity in Mg 3 Sb 2 -related structures. This work extends our understanding of structure and properties based on chemical bonding analysis, and it will guide the search for and design of materials with tailored anisotropic properties.
The concept of secondary building units (SBUs) is central to all science on metal‐organic frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during ...MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) analysis was used to probe UiO‐66 formation under solvothermal conditions. The expected SBU—a hexanuclear zirconium cluster—is present in the metal salt precursor solution. Addition of organic ligands results in a disordered structure with correlations up to 23 Å, resembling crystalline UiO‐66. Heating leads to fast cluster aggregation, and further growth and ordering results in the crystalline product. Thus, SBUs are present already at room temperature and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis.
Nucleation: In situ pair distribution function analysis was used to reveal the atomic scale nature of precursor species during solvothermal UiO‐66 MOF synthesis, and a hexanuclear zirconium cluster was established as the secondary building unit present, even in the metal salt precursor solution.
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•Phase pure rutile SnO2 NPs were synthesized by a continuous flow hydrothermal method.•SnO2 NPs prepared with considerable size and morphology control.•At low and high pH obtained ...nanorods under near critical or supercritical conditions.•SnO2 nanoparticles with 3.5 nm in size had BET of 185 m2. g-1 and a band gap of 4.0 eV.•The initial discharge capacity of SnO2 produced at 250 °C was 1378 mA h.g-1.
SnO2 nanoparticles have been prepared by a continuous flow hydrothermal method using SnCl4∙5H2O and aqueous sodium hydroxide as precursor solutions. The syntheses were carried out in an experimental matrix of four different precursor pH values (1, 3, 7 and 11) and four different temperatures (250, 300, 350, 400 °C). Both temperature and pH affect the crystallite size and morphology providing considerable synthesis control over the nanoparticle characteristics. At intermediate pH (3 and 7) quite spherical nanoparticles are obtained and higher synthesis temperature results in larger nanoparticles (3–6 nm). A highly peculiar behavior is observed at either low pH (1) or high pH (11), where larger anisotropic nanorods (width 6−9 nm, length 20−40 nm) are obtained for the reaction near or in the supercritical regime (350 and 400 °C). Pore size and band gap were determined for all products, and selected samples were tested as anode materials in Li ion batteries.
Supercritical growth: The formation and evolution of ceria nanoparticles during hydrothermal synthesis was investigated by in situ total scattering and powder diffraction. The nucleation of pristine ...crystalline ceria nanoparticles originated from previously unknown cerium dimer complexes. The nanoparticle growth was highly accelerated under supercritical conditions.
The surface of a topological insulator plays host to an odd number of linearly-dispersing Dirac fermions, protected against back-scattering by time-reversal symmetry. Such characteristics make these ...materials attractive not only for studying a range of fundamental phenomena in both condensed matter and particle physics, but also for applications ranging from spintronics to quantum computation. Here, we show that the single Dirac cone comprising the topological state of the prototypical topological insulator Bi2 Se3 can co-exist with a two-dimensional electron gas (2DEG), a cornerstone of conventional electronics. Creation of the 2DEG is tied to a surface band-bending effect, which should be general for narrow-gap topological insulators. This leads to the unique situation where a topological and a non-topological, easily tunable and potentially superconducting, metallic state are confined to the same region of space.
The superionic conductor Cu2−xSe has regained interest as a thermoelectric material owing to its low thermal conductivity, suggested to arise from a liquid-like Cu substructure, and the material has ...been coined a phonon-liquid electron-crystal. Using high-quality three-dimensional X-ray scattering data measured up to large scattering vectors, accurate analysis of both the average crystal structure as well as the local correlations is carried out to shed light on the Cu movements. The Cu ions show large vibrations with extreme anharmonicity and mainly move within a tetrahedron-shaped volume in the structure. From the analysis of weak features in the observed electron density, the possible diffusion pathway of Cu is identified, and it is clear from its low density that jumps between sites are infrequent compared with the time the Cu ions spend vibrating around each site. These findings support the conclusions drawn from recent quasi-elastic neutron scattering data, casting doubt on the phonon-liquid picture. Although there is diffusion of Cu ions in the structure, making it a superionic conductor, the jumps are infrequent and probably not the origin of the low thermal conductivity. From three-dimensional difference pair distribution function analysis of the diffuse scattering data, strongly correlated movements are identified, showing atomic motions which conserve interatomic distances at the cost of large changes in angles.
Crystal structure and phase transition of thermoelectric SnSe Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo
Acta crystallographica Section B, Structural science, crystal engineering and materials,
June 2016, Letnik:
72, Številka:
3
Journal Article
Recenzirano
Tin selenide‐based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh ...thermoelectric figure of merit of 2.6 ± 0.3 in the high‐temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high‐resolution synchrotron powder X‐ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high‐temperature phase transition (∼ 810 K). Anharmonic Gram–Charlier parameters have been refined, but data from single‐crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low‐temperature and high‐temperature phases are discussed. It is also shown that the high‐temperature Cmcm phase is not pseudo‐tetragonal as commonly assumed.
The crystal structure of SnSe is investigated through high‐resolution synchrotron powder X‐ray diffraction in the range 100–855 K. The temperature dependence of the lattice constants, fractional coordinates, site occupancy factors and atomic displacement parameters is studied.
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