类MgB2硼化物晶体电子结构比较研究

应用准确的第一原理方法，对8种类MgB₂超导体结构的二硼化物进行了电子结构 比较研究，发现其中的超导体具有特殊的能带属性.对其在高压下态密度的变化情况做了对照. 关键词： 硼化物 态密度 能带 高压     

苯酚装置中物料的定性定量分析

苯酚是一种重要的基本有机化工原料,广泛用于双酚A、酚醛树脂、环氧树脂、医药、农药、炸药和染料等方面。燕化公司苯酚丙酮装置是采用异丙苯法生产的。其原理是原料苯和丙烯在催化剂存在下反应生成异丙苯,异丙苯与空气中的氧反应生成过氧化氢异丙苯,在硫酸催化剂存在下,过氧化     

Magnetoresistance and magnetic properties of Fe3O4 nanoparticle compacts

In this paper,we report on the magnetic properties of Fe3O4 nanoparticles with different grain sizes under different pressures.In all the samples,the saturated magnetization Ms shows a linear decrease with increasing pressure.The thickness of the magnetic dead layer on the nanoparticle surface nuder different pressures was roughly estimated,which also increases with increasing pressure.The transport measurements of the nanoparticle Fe3O4 compacts show that the low-field magnetoresistance (MR) value is insensitive to the grain size in a wide temperature range;however,the high-field MR value is dependent on grain size,especially at low temperatures.These experimental results can be attributed to the different surface states of the nanoparticles.     

南海海绵Gellius Cymiformis中的一个新神经酰胺

从中国南海海绵 Gellius Cymiformis(Esper)中首次分离到一个新的神经酰胺 Gecymiamide—A(I),通过各种波谱分析推导其化学结构。     

Effects of pressure and/or magnetism on superconductivity of δ-MoN single crystal

Effects of pressure and/or magnetism on the critical superconducting temperature(Tc)ofδ-Mo N single crystal were investigated using a Maglab system.Theδ-Mo N single crystal was synthesized at extreme conditions of high pressure and high temperature.The carrier density ofδ-Mo N single crystal as a function of applied pressure was determined using Hall coefficient measurement.     

Superconductivity in Topological Semimetal θ-TaN at High Pressure

Recently,θ-TaN was proposed to be a topological semimetal with a new type of triply degenerate nodal points.Here,we report studies of pressure dependence of transport,Raman spectroscopy and synchrotron x-ray diffraction on θ-TaN up to 61 GPa.We find that θ-TaN becomes superconductive above 24.6 GPa with T_c at 3.1 K.The θ-TaN is of n-type carrier nature with carrier density about 1.1 × 10~(20)/cm~3 at 1.2 GPa and 20 K, while the carrier density increases with the pressure and saturates at about 40 GPa in the measured range.However,there is no crystal structure transition with pressure up to 39 GPa,suggesting the topological nature of the pressure induced superconductivity.     

Y_1Ba_2Cu_3O_(7-δ)的氧离子缺位数,氧空穴数变化与结构相变的关系

在空气、氮气、真空(10~(-3)乇)、氧气等气氛条件下,利用高温 X 射线动态跟踪法和 TG-DTA测定了 Y_1Ba_4Cu_3O_(7-δ)的结构和氧缺位量随温度的变化,注意到不同气氛对超导体中晶格氧和吸附氧的动态平衡的影响;测得氧缺位量δ与晶体结构转变之间的关系.根据文献[11]关于Cu-O 间电子转移的结论,计算出 Cu-O_2层中 O 的平均空穴数 n_h 与结构变化的对应关系.O≤δ≤0.25,0.25≥n_h≥0.125为正交超导相的稳定区,氧的空穴浓度为(1.44—0.72)x10~(21)/cm~30.25≤δ<0.5,0.125≥n_k>0为正交、四方相的转变过渡区;0.5≤δ≤1,n_h=0为四方非超导相的稳定区.因此,除了四方非超导结构区氧负离子取2价外,其它情况氧负离子也不总是取负2价.     

Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca_2CuO_2Cl_2

The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified:a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.     

Effect of Annealing on Ferroelectric Properties of Nanometre BaTiO3 Ceramics Prepared by High Pressure Sintering Method

Dense nanocrystalline BaTiO3 ceramics with a grain size of 5Onto are prepared under 6 GPa at 1273K using a high pressure sintering method. The sintered bulk is uniform and the relative density is above 97%. We anneal the ceramic samples in oxygen with various temperatures and for the annealing, several broadened peaks can be observed at different times without apparent grain growth. After about 378K（ by dielectric measurements. However, these peaks are very different from those of coarser-grained ceramics. It is indicated that both the elimination of oxygen vacancies and the release of residual stresses caused by high pressure greatly improve the overall ferroelectric properties of BaTiO3 ceramics. The observation of nearly linear polarization hysteresis loop after anneal provides the solid evidence of ferroelectricity in these nano-sized BaTiO3 ceramics. It is believed that the absence of 90° domains and the existence of poor-permittivity nonferroelectric grain boundaries contribute to the slim loop.     

Metallization of Cu3N Semiconductor under High Pressure

Using the four-probe method, we investigate the electrical conductivity of Cu3N under high pressure with the diamond anvil cell. Cu3N is a semiconductor at ambient pressure showing a band gap about l eV. With the application of quasi-hydrostatic pressures, its resistance decreases dramatically over five orders of magnitude from ambient to 9 GPa. The compound became a metal at pressure about 5.5 GPa, which is in well agreement with the recent first principle calculation.