First-principles study, fabrication and characterization of (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramic

The formation possibility of a new (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramic (ZHC-1) was first analyzed by the first-principles calculations and thermodynamical analysis and then it was successfully fabricated by hot pressing sintering technique. The first-principles calculation results showed that the mixing enthalpy of ZHC-1 was 5.526 kJ/mol and the mixing entropy of ZHC-1 was in the range of 0.693R-1.040R. The thermodynamical analysis results showed that ZHC-1 was thermodynamically stable above 959 K owing to its negative mixing Gibbs free energy. The experimental results showed that the as-prepared ZHC-1 (95.1% relative density) possessed a single rock-salt crystal structure, some interesting nanoplate-like structures and high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, compared with the initial metal carbides (ZrC, NbC, TiC and VC), it showed a relatively low thermal conductivity of 15.3 + - 0.3 W/(m.K) at room temperature, which was due to the presence of solid solution effects, nanoplates and porosity. Meanwhile, it exhibited the relatively high nanohardness of 30.3 + - 0.7 GPa and elastic modulus of 460.4 + - 19.2 GPa and the higher fracture toughness of 4.7 + - 0.5 MPa.m1/2, which were attributed to the solid solution strengthening mechanism and nanoplate pullout and microcrack deflection toughening mechanism.Comment: 49 pages,6 figures, 4 table

Quantum teleportation via two qubit Heisenberg XY chain - Effects of anisotropy and magnetic field

In this paper, we study the influence of anisotropy on the usefulness, of the entanglement in a two-qubit Heisenberg XY chain at thermal equilibrium in the presence of an external magnetic field, as resource for quantum teleportation via the standard teleportation protocol. We show that the nonzero thermal entanglement produced by adjusting the external magnetic field strength beyond some critical strength is a useful resource. We also considered entanglement teleportation via two two-qubit Heisenberg XY chains.Comment: 12 pages, 1 figur

Enhancement of aldehyde-water shift reaction over CuZnAl catalyst by Mn promoter

A series of Mn promoted CuZnAl catalysts were prepared by coprecipitation method. Doping of manganese in CuZnAl strongly enhanced the AWS activity and propionic acid selectivity. The interaction between Cu and Mn ions results in suppressed the hydrogenation of propanal to propyl alcohol and enhanced the selectivity of propionic acid. According to our results, the most favorable Mn/Cu molar ratio is 1:1. Higher temperature is also beneficial to the selectivity of propionic acid on CuZnAl-based catalysts

Formation criterion for binary metal diboride solid solutions established through combinatorial methods

Establishing the formation criterion is urgent for accelerating the discovery and design of solid-solution materials with desirable properties. The previously reported formation criterion mainly focused on solid-solution alloys, while the formation criterion was rarely established in solid-solution ceramics. To solve this problem, herein, we take a class of solid-solution ceramics, namely binary metal diboride ((MxN1-x)B-2) solid solutions, as a prototype. Through combinatorial methods including high-throughput molten salt syntheses and high-throughput first-principles calculations combined with the machine learning approach, the correlation between influential factors, including atomic size difference (delta), mixing enthalpy at 0 K and 0 Pa (Delta Hmix0K), doping condition (phi), and valence electron concentration (VEC), and the formation ability of (MxN1-x)B-2 solid solutions was first studied systematically, and then their formation criterion was well established. The results showed that the influential degree of the aforementioned four factors on the formation ability of (MxN1-x)B-2 solid solutions could be described as follows: delta \u3e Delta Hmix0K\u3e phi \u3e VEC. In addition, a newly proposed parameter, beta, could well reflect the formation ability of (MxN1-x)B-2 solid solutions: when beta \u3e 0, the single-phase (MxN1-x)B-2 solid solutions could be successfully synthesized in our work and vice versa. This study may provide a theoretical guidance in the discovery and design of various solid-solution ceramics, such as the metal borides, carbides, nitrides, etc, with desirable properties

Iron-chromium mixed metal oxides catalyse the oxidative dehydrogenation of propane using carbon dioxide

The oxidative dehydrogenation of propane to propene using carbon dioxide is an attractive novel synthesis route to produce a key platform chemical. We investigated iron-chromia catalysts prepared by sol-gel. The mixed oxides showed improved specific surface area and a high concentration of acid and base sites and were found to be highly active catalysts. Although coking was observed over the catalysts, oxidative regeneration restored the majority of the initial activity over 5 consecutive cycles. The initial space time yield was amongst the most active Cr-based catalysts in the literature

The reaction pathways of 5-hydroxymethylfurfural conversion in a continuous flow reactor using copper catalysts

The transformation of 5-hydroxymethylfurfural is investigated using supported and bulk copper oxide catalysts. We show that the selectivity to 5-methylfuraldehyde or 2,5-diformylfuran can be controlled by the solvent and the carrier gas. The use of water as the solvent and N2 as the carrier gas led to the highest conversion and most selective pathway to 2,5-diformylfuran. Quasi in situ X-ray photoelectron spectroscopy and H2-TPR measurements revealed that H2O can re-oxidise Cu, significantly enhancing the selectivity to 5-methylfuraldehyde. Subsequent density functional theory calculations revealed more precisely the role of water in the reaction mechanism

First‐principles study, fabrication, and characterization of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramic

The formation possibility of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramic (HHC‐1) was first analyzed by the first‐principles calculations, and then, it was successfully fabricated by hot‐pressing sintering technique at 2073 K under a pressure of 30 MPa. The first‐principles calculation results showed that the mixing enthalpy and mixing entropy of HHC‐1 were −0.869 ± 0.290 kJ/mol and 0.805R, respectively. The experimental results showed that the as‐prepared HHC‐1 not only had an interesting single rock‐salt crystal structure of metal carbides but also possessed high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, it exhibited extremely high nanohardness of 40.6 ± 0.6 GPa and elastic modulus in the range from 514 ± 10 to 522 ± 10 GPa and relatively high electrical resistivity of 91 ± 1.3 μΩ·cm, which could be due to the presence of solid solution effects.</p

Formation criterion for binary metal diboride solid solutions established through combinatorial methods

Establishing the formation criterion is urgent for accelerating the discovery and design of solid-solution materials with desirable properties. The previously reported formation criterion mainly focused on solid-solution alloys, while the formation criterion was rarely established in solid-solution ceramics. To solve this problem, herein, we take a class of solid-solution ceramics, namely binary metal diboride ((MxN1-x)B-2) solid solutions, as a prototype. Through combinatorial methods including high-throughput molten salt syntheses and high-throughput first-principles calculations combined with the machine learning approach, the correlation between influential factors, including atomic size difference (delta), mixing enthalpy at 0 K and 0 Pa (Delta Hmix0K), doping condition (phi), and valence electron concentration (VEC), and the formation ability of (MxN1-x)B-2 solid solutions was first studied systematically, and then their formation criterion was well established. The results showed that the influential degree of the aforementioned four factors on the formation ability of (MxN1-x)B-2 solid solutions could be described as follows: delta > Delta Hmix0K> phi > VEC. In addition, a newly proposed parameter, beta, could well reflect the formation ability of (MxN1-x)B-2 solid solutions: when beta > 0, the single-phase (MxN1-x)B-2 solid solutions could be successfully synthesized in our work and vice versa. This study may provide a theoretical guidance in the discovery and design of various solid-solution ceramics, such as the metal borides, carbides, nitrides, etc, with desirable properties.</p