Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

Magnetic ordering temperatures in heavy rare earth metal dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to a pressure of 69 GPa and a temperature of 10 K. Previous studies using magnetic susceptibility measurements at high pressures were able to track magnetic ordering temperature only till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hcp phase and finally leveling off in the distorted face centered cubic phase of Dy. Our studies reaffirm that 4f-shell remains localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.     

High pressure electrical transport behavior in organic semiconductor pentacene

The high pressure electrical transport behavior of pentacene has been investigated by alternating current impedance techniques and direct current resistivity measurement in a diamond anvil cell (DAC). The resistance decreases with increasing pressure below 17.4?GPa, while it increases above 17.4?GPa, which is caused by the transition of pentacene from an ordered state to the disordered state under higher pressure. From the Raman spectra under various pressures, pentacene becomes amorphous above 17.3?GPa, which is consistent with the impedance results. The charge transport operates in the hopping regime with charges jumping between interacting molecules, and the hopping mechanisms are related to the vibration modes. Above 17.4?GPa, the pressure dependence of the relaxation activation energy is 21.7?meV/GPa and pentacene keeps semiconductor characteristics up to 28.3?GPa.     

Diamond-anvil cell high pressure X-ray studies on thorium to 100 GPa

Abstract

High pressure crystal structural changes and volume compression for thorium were investigated to 100 GPa in a diamond-anvil cell apparatus using the energy-dispersive X-ray diffraction technique. No structural change was observed in this pressure range. However, a slope change in the P-V curve was observed between 20 and 30 GPa. We surmise that this break in the slope may be due to an electronic transformation.     

Diamond anvil cell, 50th birthday

The year 2008 marked the fiftieth birthday of the diamond anvil cell. Its birth took place when Alvin Van Valkenburg, while working with his colleagues, Charles E. Weir, Ellis R. Lippincott, and Elmer N. Bunting, first realized that he could look right through one of the diamond anvils and see a sample while it was at high pressure. In the following years, these scientists and many others adapted the diamond anvil cell to a wide variety of analytical techniques that have provided an impressive amount of information about materials at high pressures and high temperatures. But, virtually all of those techniques start with looking into the diamond anvil cell.     

To the synthesis of polycrystalline diamond

Abstract

The sintering system “Diamond-Graphite-Cobalt” is investigated by means of a High Pressure - High Temperature - Belt - Apparatus. Described are the sintering conditions used and some of the properties of the compacts obtained. Good sintering structures and hard PCD (up to 50 GPa) were obtained at 7,5 GPa and 1500°C.     

氮掺杂的金刚石磁性研究

采用第一性原理计算方法研究金刚石中由空位或者N掺杂引起的磁特性. 发现-1价和-2 价的碳空位能分别产生3 μ_B和2μ_B的磁矩; -2价的碳空位能够引发长程有序的铁磁耦合状态, 而-1价的碳空位更倾向于反铁磁耦合.掺杂N元素能有效地控制空位的荷电状态及相应的磁相互作用, 这一结果为在金刚石中实现非过渡族金属掺杂的铁磁性提供了一条新的路径. 关键词： 第一性原理计算 氮掺杂 金刚石 磁性     

Square‐Wave Voltammetry Determination of Aspartame in Dietary Products Using a Boron‐Doped Diamond Electrode

Abstract

The use of square‐wave voltammetry in conjunction with a cathodically pretreated boron‐doped diamond electrode for the analytical determination of aspartame in dietary products is described. In this determination, the samples were analyzed without previous treatment in a 0.5 mol l^?1 H₂SO₄ solution. A single oxidation peak at a potential of 1.6 V vs. Ag/AgCl (3.0 mol l^?1 KCl) with the characteristics of an irreversible reaction was obtained. The analytical curve was linear in the aspartame concentration range 9.9×10^?6 to 5.2×10^?5 mol l^?1 with a detection limit of 2.3×10^?7 mol l^?1. The relative standard deviation (n=5) obtained was smaller than 0.2% for the 1.0×10^?4 mol l^?1 aspartame solution. The proposed method was applied with success to the determination of aspartame in several dietary products and the results were similar to those obtained using an HPLC method at 95% confidence level.     

The Use of Ultrasound for the Analytical Determination of Nitrite on Diamond Electrodes by Square Wave Voltammetry

Abstract

This work describes an analytical methodology for the determination of nitrite ions in aqueous solutions using boron‐doped diamond electrodes and square wave voltammetry associated with ultrasound radiation. The nitrite ions were oxidized to nitrate ions in Britton‐Robinson buffer solutions 0.1 M, pH 2.0 at 1.0 V versus Ag/AgCl. The voltammetric response of nitrite in the presence of ultrasound showed a peak current five times higher than the obtained in silent conditions. Thus, the detection limit obtained in the presence of radiation was 17 nM (0.782 µg l^?1), a small value if compared with that obtained in the absence of ultrasound: 140 nM (6.44 µg l^?1).     

The high‐temperature tribological properties of Si‐DLC films

The tribological properties of Silicon‐containing diamond‐like‐carbon (Si‐DLC) films, deposited by magnetron sputtering Si target in methane/argon atmosphere, were studied in comparison with diamond‐like‐carbon (DLC) films. The DLC films disappeared because of the oxidation in the air at 500 °C, whereas the Si‐DLC films still remained, implying that the addition of Si improved significantly the thermal stability of DLC films. Retarded hydrogen release from DLC film at high temperature and silicon oxide on the surface might have contributed to lower friction coefficient of the Si‐DLC films both after annealing treatment and in situ high‐temperature environment. Copyright © 2012 John Wiley & Sons, Ltd.