Effect of SiO2 nanoparticles sizes on the optical properties and radiation resistance of powder mixtures ZrO2 with micron sizes

One way to improve photo- and radiation resistance of materials is by the modification of their nanoparticles. The purpose of work is to study the optical properties and radiation resistance of ZrO₂ powder mixtures with SiO₂ nanoparticles without high-temperature heating. The ZrO₂ powders with micron sizes were mixed in a ratio of 100:7 mas.% with SiO₂ nanopowders. The nanopowders were obtained by combustion of silicon tetrachloride in air plasma. Samples were characterized using X-ray diffraction (XRD), high resolution scanning electron microscopy (SEM), and a simulator of the environment of outer space “Spectrum”. The radiation resistance increase of zirconia dioxide powders with micron-sized grains by the addition of silica nanoparticles without heating at a high temperature was found. For these purposes only water evaporation at 150 °C was used. The effectiveness of the modification reaches values of 2.1 times. This value is close to or even more in comparison to its values in the modification by using high-temperature heating. This result is significant for the practical use of this method of incensement of the radiation resistance of oxide reflecting powders.     

基于第一性原理研究Y掺杂锐钛矿TiO2的磁光性质

基于第一性原理计算,建立了未掺杂和三种Y掺杂量的锐钛矿TiO2模型。对各个模型的形成能、磁性、电子结构及吸收光谱进行了计算。结果表明：掺入锐钛矿晶格的不同Y原子之间没有团簇趋势;Y掺杂量越大,实现掺杂所需的能量越高;Y掺杂的锐钛矿体系具有铁磁性,因而晶格中的自旋能级分裂效应能降低锐钛矿的带隙宽度,但当Y掺杂量升高时,这种影响显著减弱;随着Y掺杂量增加,弱束缚的O-2p态电子浓度增加,导致价带顶的O-2p态跨越费米能级,使得带隙值减小,进而提高了改性锐钛矿TiO2对可见光的吸收系数。     

超高比表面积碳气凝胶常压干燥制备与结构分析

以间苯二酚(R)-甲醛(F)为原料,加入表面活性剂P123以增强材料的骨架强度的方法,采用常压干燥技术制备了RF碳气凝胶,并进行了二氧化碳活化以调节其孔结构。扫描电子显微镜(SEM)测试表明,常压干燥的碳气凝胶结构中具有更大的纳米颗粒,骨架结构变粗,活化使碳气凝胶骨架结构更加致密;红外吸收光谱(FTIR)表明,表面活性剂P123中的醚键与RF苯环中的羟基存在强的相互作用,碳化后P123特征峰消失;热重曲线(TG和DTG)分析说明P123在440 ℃左右分解完全,不会对碳气凝胶的成分产生影响,并能起到良好的造孔作用;氮气吸附表明常压干燥制备的碳气凝胶比表面积约为570 m2/g,活化之后的比表面积高达3 500 m2/g左右。     

超高比表面积碳气凝胶常压干燥制备与结构分析

以间苯二酚(R)-甲醛(F)为原料,加入表面活性剂P123以增强材料的骨架强度的方法,采用常压干燥技术制备了RF碳气凝胶,并进行了二氧化碳活化以调节其孔结构。扫描电子显微镜(SEM)测试表明,常压干燥的碳气凝胶结构中具有更大的纳米颗粒,骨架结构变粗,活化使碳气凝胶骨架结构更加致密;红外吸收光谱(FTIR)表明,表面活性剂P123中的醚键与RF苯环中的羟基存在强的相互作用,碳化后P123特征峰消失;热重曲线(TG和DTG)分析说明P123在440 ℃左右分解完全,不会对碳气凝胶的成分产生影响,并能起到良好的造孔作用;氮气吸附表明常压干燥制备的碳气凝胶比表面积约为570 m2/g,活化之后的比表面积高达3 500 m2/g左右。     

Model studies of the structure and optical properties of the TiO2(110) surface with an adsorbed Ag atom

ABSTRACT

The present studies of the atomic Ag adsorbate on the substrate TiO₂(110) explore the importance of dispersion (or van der Waals) energies for determining the structure of the adsorbed Ag atom, using density functional theory (DFT) supplemented by a dispersion energy treatment, within the PBE-D3 treatment. It is also of interest to explore electronic excitation by light absorption. Electronic density of states (EDOS) are obtained without and with Ag adsorbed on the TiO₂(110), to find the extent of change on the density of valence, conduction and intraband states. This is done using the hybrid HSE06 functional, which is known to provide good values for the energy band gap of the substrate. A computationally efficient PBE?+?BG procedure for these structures, which corrects the PBE band gap, is implemented to generate accurate EDOSs and light absorption intensities versus photon energies. This is followed by a reduced density matrix treatment of the dissipative dynamics of light absorption, generating state-to-state oscillator strengths and photoabsorbances for the pure and nanostructured TiO₂(110) surfaces. Adsorption of Ag leads to a noticeable increase in light absorption at visible wavelengths, and very large increases in the UV region of the spectrum.     

相分布和晶粒尺寸对Nd2Fe14B/ɑ-Fe纳米复合永磁材料矫顽力的影响

本文采用统计平均方法研究了软、硬磁性晶粒尺寸及相分布对Nd2Fe14B/α-Fe纳米复合永磁材料矫顽力的影响。计算结果表明：对于单相纳米硬磁材料，磁体矫顽力随着硬磁性晶粒尺寸的减小而降低；对于软、硬两磁性相组成的Nd2Fe14B/a-Fe纳米复合永磁材料，两相的随机分布将导致磁体矫顽力随硬磁性晶粒尺寸的减小呈现极大值。本文的计算结果还表明当硬磁性晶粒尺寸大于软磁性晶粒的最佳尺寸时(15nm)，具有多层膜结构的Nd2Fe14B/a-Fe纳米复合永磁材料将比两相随机分布时具有更大的矫顽力。