Structure of Nb/Ta layered ternary tellurides containing first row transition metal atoms

A summary of research on the structure of Nb/Ta layered tellurides in the past period is reported. 14 compounds, which have been structurally characterized by X-ray diffraction work, are presented according to their structural features. The first two compounds, Nb2CrTe4 and Nb2Cu1.48Te4, are characterized in that the ternary atoms are inserted in the different layers from the Nb atoms. While in the other compounds, both kinds of metal atoms are inserted in the same layer. The six compounds with formula M2M'2Te4(M = Nb/Ta; M' = Ni, Co, Fe) are characterized in that their structure can be described as construction by using cluster units "M2M'2Te10" as building blocks. in the two metal-rich compounds, TaCo2Te2 and TaNi2Te2, Ta atom has a distorted mono-capped pentagonal prism configuration. The structure of TaFeTe3, TaNTe3 and NbNi2.34Te3 can be described as building by the arrangement of double octahedral chains (DOC), in this con-nection, a selenide Ta2Ni2Se5 is also included by using the second type of     

Ni7−δSnTe2: Modulated crystal structure refinement, electronic structure and anisotropy of electroconductivity

Single crystals of Ni_7−δSnTe₂ were grown during re-crystallization of the presynthesized powder in a two zone furnace. The modulated structure was solved and refined in the (3+2)-dimensional superspace group I4/mmm(0-α0, α00)0.ss.mm with lattice parameters a=3.759(1) and c=19.410(2) Å (measured at 153 K) and Z=2. Satellite reflections observed in the diffraction images can be assigned to the incommensurate modulation vectors q₁=da* and q₂=db* with d=0.410(1). The composition resulting from X-ray structure refinement is Ni_5.81SnTe₂. The structure model has been also developed in the orthorhombic (3+1)-dimensional superspace group Immm(α00)00s assuming twinning according to [110], giving thus the composition Ni_5.79SnTe₂. The origin of the modulation can be attributed to a variation of the occupancy of the Ni(3) site in Ni/Te slabs of the structure. Band structure calculations on a commensurate approximant and single crystal electrical resistivity measurements reveal anisotropic metallic conductivity for this compound.     

稀土元素对ZrO2-M2O3/MCM-41(M=La,Ce,Sm,Gd)氢转移催化活性的影响

通过浸渍法制备了5%ZrO₂/MCM-41、5%ZrO₂-5%M₂O₃/MCM-41(M=La,Ce,Sm,Gd)催化剂,考察其在苯乙酮氢转移还原生成-苯乙醇反应中的催化活性,同时对样品进行XRD、N₂吸附-脱附、吡啶吸附原位红外等表征分析,研究添加稀土金属氧化物对催化剂活性的影响机理。结果表明:ZrO₂及稀土金属氧化物均以无定型态或粒度低于XRD检测限的细小晶粒较好地分散在MCM-41介孔分子筛内表面;加入稀土金属氧化物对ZrO₂/MCM-41的催化活性有较大影响,催化活性按5%ZrO₂-5%La₂O₃/MCM-41>5%ZrO₂-5%Sm₂O₃/MCM-41>5%ZrO₂-5%Gd₂O₃/MCM-41>5%ZrO₂/MCM-41>5%ZrO₂-5%Ce₂O₃/MCM-41降低。这一方面归因于加入稀土金属氧化物增强了催化剂表面Zr-OH、L酸中心及B酸中心的酸性,另一方面归因于La₂O₃的加入使催化剂表面酸中心数目明显提高,Sm₂O₃、Gd₂O₃的加入使催化剂表面酸中心数目有所降低,而加入Ce₂O₃使催化剂表面酸中心数目显著减少。     

Impacts of oxygen sensitization methods on the deposition and microstructure of ternary lead chalcogenide alloys

Oxygen sensitization and incorporation of ternary lead chalcogenide PbSe_1-xTe_x thin films was investigated with two methods: adding oxygen via PbO to the bulk source alloy and post-deposition oxygen annealing. Characterization of the composition, structure, and morphology of these films confirmed that they follow Vegard's law for lattice parameter, and adding PbO to the source alloy did not impact the lattice parameter. However, adding PbO changed the electrical carrier properties observed in Hall effect measurements without forming any new oxide phase. Conversely, post-deposition annealing increased the lattice parameter due to oxygen incorporation into the lattice via interstitials in samples with appropriate grain boundary orientations. Morphological analysis revealed that PbSe_0.8Te_0.2 films demonstrated (100) texture, while PbSe_0.6Te_0.4 films demonstrated (111) texture with resulting grain boundary orientations more favorable to oxygen diffusion and incorporation. This varying oxygen incorporation from PbO source and oxygen annealing methods reveals trends that can lead to improved photodetector performance.     

希土元素异硫氰酸盐与二甲基乙酰胺配合物的标准生成焓的测定

本文测量了298.15K时La、Ce、Pr、Nd、Sm、Eu、Gd、Dy、Ho、Yb、Y十一种希土元素异硫氰酸盐水合物[RE(NCS)₃·nH₂O]在二甲基乙酰胺(DMA)水溶液中的积分溶解热以及相应的十一种希土元素异硫氰酸盐二甲基乙酰胺配合物[RE(NCS)₃·mDMA]在水中的积分溶解热。藉助于本文所设计的热化学循环,用本文所测得的积分溶解热数据和文献数据,求得了这十一种RE(NCS)₃·mDMA的标准生成焓,进而计算出了它们的晶格能。此外,还对Tb、Er、Tm、Lu四种RE(NCS)₃·mDMA的相应数据进行了估算。     

Selenium‐Enriched Nickel Selenide Nanosheets as a Robust Electrocatalyst for Hydrogen Generation

To address the urgent need for clean and sustainable energy, the rapid development of hydrogen‐based technologies has started to revolutionize the use of earth‐abundant noble‐metal‐free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite‐type transition‐metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se‐enriched NiSe₂ nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm^?2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H⁺ into H₂ is due to the presence of an excess of selenium in the NiSe₂ nanosheet surface.     

Simulation by Molecular Dynamics of Erbium-Activated Silica-Titania Glasses

Rare-earth doped silicate-based glasses are widely used in telecommunication technology. A limitation in the performance of active optical devices such as amplifier comes from the rare-earth clustering. Simulation methods give complementary informations to the spectroscopic usual investigations. We present a molecular dynamics simulation of a SiO₂-TiO₂:Er³⁺ system in varying its composition. Different distribution functions have been analyzed in order to have information about the clustering of erbium. To this purpose, the titanium distribution has been studied for concentration 7.8 and 15.7% Ti/(Ti + Si). We have simulated the structure of the system doped with 1 and 2.3 mol%. A calculation of the crystal field strength for the different kinds of erbium site has been interpreted in the light of the local structure. The important trend of erbium for clustering in our modeled system has been explained by the energetic requirements of the rare-earth.