Tb3Pd2, Er3Pd2 and Er6Co5–x: structural variations and bonding in rare‐earth‐richer binary intermetallics

The three binary Tb/Er‐rich transition metal compounds Tb₃Pd₂ (triterbium dipalladium), Er₃Pd₂ (trierbium dipalladium) and Er₆Co_5–x (hexaerbium pentacobalt) crystallize in the space groups Pbam (Pearson symbol oP20), P4/mbm (tP10) and P6₃/m (hP22), respectively. Single crystals of Tb₃Pd₂ and Er₆Co_5–x suitable for X‐ray structure analysis were obtained using rare‐earth halides as a flux. Tb₃Pd₂ adopts its own structure type, which can be described as a superstructural derivative of the U₃Si₂ type, which is the type adopted by Er₃Pd₂. Compound Er₆Co_5–x belongs to the Ce₆Co_2–xSi₃ family. All three compounds feature fused tricapped {TR₆} (R = rare‐earth metal and T = transition metal) trigonal prismatic heterometallic clusters. R₃Pd₂ is reported to crystallize in the U₃Si₂ type; however, our more detailed structure analysis reveals that deviations occur with heavier R elements. Similarly, Er₆Co_5–x was assumed to be stoichiometric Er₄Co₃ = Er₆Co_4.5. Our studies reveal that it has a single defective transition‐metal site leading to the composition Er₆Co_4.72(2). LMTO (linear muffin‐tin orbital)‐based electronic structure calculations suggest the strong domination of heteroatomic bonding in all three structures.     

A study on the spectral,microstructural, and magnetic properties of Eu–Nd double-substituted Ba0.5Sr0.5Fe12O19 hexaferrites synthesized by an ultrasonic-assisted approach

In this study, an examination on the spectral, microstructural, and magnetic characteristics of Eu–Nd double-substituted Ba_0.5Sr_0.5Fe₁₂O₁₉ hexaferrites (Ba_0.5Sr_0.5Nd_xEu_xFe_12−2xO₁₉ (x = 0.00–0.05) HFs) fabricated by an ultrasonic-assisted approach has been presented. An UZ SONOPULS HD 2070 ultrasonic homogenizer with frequency of 20 kHz and power of 70 W was used. The chemical bonding, structure and the morphology of the products were evaluated by Fourier-Transform Infrared (FT-IR) Spectroscopy, XRD (X-ray diffraction), scanning and transmission electron microscopy and techniques. The textural properties of the prepared nanomaterials were examined by using the Brunauer-Emmett-Teller (BET) method. The magnetic properties were studied using a vibrating sample magnetometer (VSM) at room temperature (RT) and low temperature 10 K. The magnitudes of various magnetic parameters including M_s (saturation magnetization), M_r (remanence) and H_c (coercivity) were estimated and evaluated. The M-H loops revealed the hard ferrimagnetic nature for all products at both temperatures. The M_s and M_r values showed a decreasing tendency with increasing degree of Eu³⁺ and Nd³⁺ substitutions whereas H_c values displayed an increasing trend. At RT, M_s, M_r and H_c values lie in the ranges of 63.0–68.8 emu·g⁻¹, 24.6–39.2 emu·g⁻¹ and 2252.4–2782.1 Oe, respectively. At 10 K, the values of M_s, M_r and H_c lie between 87.5–97.1 emu·g⁻¹, 33.5–40.1 emu·g⁻¹ and 2060.6–2417.2 Oe, respectively. The observed magnetic properties make the prepared products promising candidates to be applied in the recording media.     

Color tuning of up-conversion emission in ytterbium,erbium, aluminum tri-doped zinc oxide crystal by adjusting aluminum concentration

Ytterbium, erbium, aluminum tri-doped zinc oxide crystal was synthesized, which can turn color from red to green up-conversion luminescence through adjusting aluminum content. When the aluminum concentration reached 4?mol%, the color of up-conversion emission first turn from red to green. Meanwhile, the ratio of red to green emission reduced from 25.32 to 0.26, and the coordinates of chromaticity coordinate calculation changes from (0.5749, 0.3378) to (0.2190, 0.7169) with aluminum concentration range from 0 to 4?mol%. The up-conversion emission peaks at 521, 542, and 660?nm of sample originate from the transitions of ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 of erbium ions, respectively. X-ray diffraction patterns perform the better crystallization degree with increasing aluminum concentration. The scanning electron microscopy images show the porous and lamellar structures with different aluminum concentrations. A convenient but effective design to obtain ytterbium, erbium, aluminum tri-doped zinc oxide up-conversion luminescence is reported, which can turn color from red to green.     

Über die Isotopenzusammensetzung des Schwefels in seinem natürlichen Kreislauf

Es wird ein Modell des globalen Kreislaufs der Isotope des Schwefels erarbeitet, auf dessen Grundlage die säkularen Veränderungen der Isotopenzusammensetzung des Schwefels in sedimentären Sulfiden, in organisch gebundenem Schwefel und in sedimentären Sulfaten verstanden werden können. Das Modell berücksichtigt die Venwitterung von Magmatiten und sedimentärem Schwefel unter Oxydation von Sulfid zu Sulfat, die Verwitterung sedimentärer Sulfate, die Bildung sedimentärer Sulfide und organisch gebundenen Schwefels, die Bildung sedimentärer Sulfate, die Metamorphose der Sedimente und die Überführung sedimentären Schwefels in die Ozeane durch vulkanische Prozesse. Es wird gezeigt, daß nur die Isotopieeffekte bei der mikrobiellen Reduktion von Sulfat zu Sulfid, bei der Assimilation von Sulfaten durch die Pflanze und bei der Verwitterung sedimentärer Sulfide und organisch gebundenem Schwefel unter Oxydation von Sulfid zu Sulfat Einfluß auf die globale Isotopenzusammensetzung des Schwefels in den Sedimenten haben können. Im Wechselspiel dieser Prozesse kommen die säkularen Verānderungen der δ³⁴S-Werte, insbesondere die charakteristischen Schwankungen der δ³⁴S-Werte zustande. Dabei begünstigen starke Meeresbedeckungen der Erdoberfläche und warmes Klima die mikrobielle Reduktion von Sulfat zu Sulfid in den Ozeanen und führen zum Sinken bzw. Steigen der δ³⁴S-Werte in den sedimentären Sulfiden und im organisch gebundenen Schwefel bzw. in den sedimentären Sulfaten. Regressionen der Ozeane und kaltes Klima, insbesondere Vereisungen begünstigen die Verwitterung und Oxydation von Sulfiden zu Sulfaten und führen zu einem Steigen bzw. Sinken der δ³⁴S-Werte in den sedimentären Sulfiden und im organisch gebundenen Schwefel bzw. in den sedimentären Sulfaten.     

Surface modifications of crystalline SiO2 and Al2O3 induced by energetic heavy ions

Abstract

Glasses with composition × CoO.(0.25-x) CaO.0.75 B₂O₃ have been prepared over the range 0 ≤ x ≤ 0.25 containing 2 mol% of V₂O₅. Electron paramagnetic Resonance spectra of VO²⁺ of these glasses has been measured at X-band (ν ≈ 9.15 GHz) at room temperature and at liquid nitrogen temperature. Spin Hamiltonian parameters of the VO²⁺ ions have been calculated. It is found that for x ≤ 0.12 the octahedral symmetry of the V⁴⁺ site is improved. A part of these glasses were annealed at 473 K for 24 hours and EPR spectra were recorded and analysed.     

脉冲强磁场下稀土材料的发光行为研究

脉冲强磁场具有峰值磁场强及扫场速度快的特点,在一个磁场脉冲内可获得从零场到最高磁场强度的全部数据,因而测量结果具有较高的精确度和对比度。稀土发光材料因具有发光谱线丰富、发光效率高的特点,在照明、显示和传感等领域有着广泛的应用。在强磁场作用下,稀土发光材料展现出发光强度和颜色可调的特征,在磁场传感、磁场标定和磁控发光器件等方面有重要应用价值。文章利用武汉国家脉冲强磁场科学中心磁光测量装置,系统地研究了铒、铕等稀土元素掺杂的发光材料在脉冲强磁场作用下的发光光谱、发光强度以及精细能级结构等特征随磁场变化的规律,初步探索了脉冲强磁场下的磁光谱在晶体结构分析、能级结构确定、磁场标定以及磁场传感等方面的应用。     

Importance sampling algorithms for first passage time probabilities in the infinite server queue

This paper applies importance sampling simulation for estimating rare event probabilities of the first passage time in the infinite server queue with renewal arrivals and general service time distributions. We consider importance sampling algorithms which are based on large deviations results of the infinite server queue, and we consider an algorithm based on the cross-entropy method, where we allow light-tailed and heavy-tailed distributions for the interarrival times and the service times. Efficiency of the algorithms is discussed by simulation experiments.     

Theoretical and experimental investigations of complexation with BF3.Et2O effects on electronic structures,energies and photophysical properties of Anil and tetraphenyl (hydroxyl) imidazol

The novel compounds (E)‐2‐(((4‐hydroxyphenyl)imino)methyl)phenol, Tetraphenyl (hydroxyl) imidazole and their corresponding Boron difluoride complexes were synthesized and characterized by spectroscopic techniques. Density functional theory calculations at B3LYP‐D3/6–311++G (d, p) level of theory were performed for the geometric parameters. The MEP surface studies were used to understand the behavior of molecules in terms of charge transfer and to determine how these molecules interact. We used the GIAO and the B3LYP‐D3 with a 6–311++ G (d, p) basis set to simulate the (¹H‐NMR and ¹⁹F‐NMR) and the IR spectra, respectively. The corresponding calculated results are in good agreement with the experimental data. The stability of the molecule arising from hyperconjugation interaction and charge delocalization were analyzed using NBO analysis. FMOs revealed the occurrence of charge transfer within the molecule. The complexation using BF₃.Et₂O was also found to have remarkable effects on the electrochemical properties of the studied molecules, where (b) and (d) present lower chemical stability, higher reactivity and higher polarizability than (a) and (c), respectively. Moreover, the energy gap of (a) and (c) decreased after complexation using BF₃.Et₂O, indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. These values are the factors explaining the possible charge transfer interaction within the molecule. The absorption and emission spectra of the model compound were also simulated and compared to experimental observations in the DMF solvent. The results of DFT calculations supported the structural and spectroscopic data and confirmed the structure modification of frontier molecular orbitals for BF₂ complexes as well as tunable potentials and energy levels.     

The Synthesis of a New Type of Liquid Crystal Containing Rare Earth Element Polyoxometalate

Ｉｎｔｈｉｓｌｅｔｅｒ,ｐｏｌｙｏｘｏｍｅｔａｌａｔｅ（ＮＨ４）１７［Ｃｅ（α２－Ｐ２Ｗ１７Ｏ６１）２］ｘＨ２Ｏ,ａｓａｎｅｗｔｙｐｅｏｆｌｉｑ－ｕｉｄｃｒｙｓｔａｌ,ｉｓｆｉｒｓｔｌｙｒｅｐｏｒｔｅｄ．Ｔｈｅｉｒｐｒｏｐｅｒｔｉｅｓｒｅｌｅｖａｎｔ...     

镍基甲烷化催化剂中的助剂作用 Ⅱ重稀土氧化物添加剂的结构效应和电子效应

应用ＢＥＴ、气相色谱、红外光谱、竞争加氢反应和ＸＰＳ等方法,在以前工作的基础上继续考察了Ｙ２Ｏ３、Ｓｍ２Ｏ３、Ｅｕ２Ｏ３、Ｇｄ２Ｏ３、Ｔｂ４Ｏ７、Ｄｙ２Ｏ３、Ｅｒ２Ｏ３、Ｔｍ２Ｏ３、Ｙｂ２Ｏ３作为添加剂,对镍在γ－Ａｌ２Ｏ３表面的分散度、甲烷化活性、ＣＯ在镍上的吸附态及表面镍原子的电子状态的影响．结果表明,稀土氧化物添加剂不仅明显地提高了金属镍的分散度和甲烷化活性,还直接地影响表面镍原子的电子状态．对不同稀土氧化物,这些效应各异．作者认为,利用稀土氧化物添加剂调节表面镍原子的电子状态,可能成为改进甲烷化催化剂活性的一个有效途径．