Tao ZHU
,
Gaorong HAN
,
Gaoling ZHAO and Zishang DING(Dept. of Materials Science and Engineering
,
Zhejiang University
,
Hangzhou 310027
,
China)( State Key Lab. of Magnetism
,
Institute of Physics
,
Chinese Academy of Sciences
,
P.O.Box 603
,
Beijing 100080
,
China)
材料科学技术（英文）
Raman spectra of the PbTiO3 films via sol-gel process were investigated by using a Jobin Yvon U1000 system. Compared with the Raman spectra of the PbTiO3 single crystals, Raman peaks of PbTiOs films shift downward, which is attributed to the stress effect in the PbTiO3 films exerted by the substrate and the size effect on the Raman frequencies
关键词:
Journal of Physics-Condensed Matter
The spin-polarized generalized gradient approximation within the plane-wave pseudopotential density functional theory is employed to investigate the magnetism and phase transition of iron under pressure. It is found that iron has a ferromagnetic body-centered-cubic (bcc) ground state, while at high pressure (such as at the Earth's lower mantle and core pressure), the most stable phase is the nonmagnetic hexagonal-close-packed (hcp) phase. For the face-centered-cubic (fcc) iron, we find that there is an intermediate-spin state (IS) during the transformation from the high-spin state (HS) to the low-spin (LS) state under pressure. The transition pressures of the HS -> IS and the IS -> LS are about 15 GPa and 50 GPa, respectively. The magnetism can affect the properties of iron up to 72.9 GPa. From the enthalpy difference between every two phases, we find the phase transition pressures of FM-bcc -> FM-hcp, FM-bcc -> NM-hcp and NM-bcc -> NM-hcp are 14.4 GPa, 29.5 GPa and 42.7 GPa, respectively.
关键词:
generalized-gradient approximation;ab-initio;pseudopotential;calculations;electronic-structure;static compression;spin transition;surface alloys;lower mantle;earths core;plane-wave
Yang LUO
材料科学技术（英文）
Due to continued growth in key markets, a broadening of application base and performance improvements, the market demands of NdFeB magnet increased steadily in 1998, and the global output of sintered NdFeB magnet exceeded 10,000 t, in spite of the economic recession in Asia. In 1998 China produced 3,850 t sintered NdFeB block magnet, with an annual growth rate of +22% over the output in 1997.
关键词:
Chunju WANG
,
Debin SHAN
,
Bin GUO
,
Jian ZHOU
,
Lining SUN
材料科学技术（英文）
From the viewpoint of production engineering, microforming is considered as an effective process to fabricate various microparts. Several key problems in microforming processes were investigated. A new microforming apparatus with a high stiffness piezoelectric actuator as the punch driver was developed to produce microparts. To improve the forming abilities and locate the billets, a floating microdie was designed. The size effects of the billets and die cavities on the microforming abilities were studied with upsetting and coining tests, respectively. And the isothermal microforming process of microgears was performed with the developed microforming apparatus. Several analysis methods were used to evaluate the forming quality of the microparts.
关键词:
Microforming
,
尺寸效应
,
微塑性成形设备
,
浮动
Express Polymer Letters
The state-of-art and key problems of carbon nanotube (CNT) based polymer composites (CNT/polymer composites) including CNT/polymer structural composites and CNT/polymer functional composites are reviewed. Based on the results reported up to now, CNTs can be an effective reinforcement for polymer matrices, and the tensile strength and elastic modulus of CNT/polymer composites can reach as high as 3600 MPa and 80 GPa, respectively. CNT/polymer composites are also promising functional composite materials with improved electrical and thermal conductivity, etc. Due to their multi-functional properties, CNT/polymer composites are expected to be used as low weight structural materials, optical devices, thermal interface materials, electric components, electromagnetic absorption materials, etc. However, the full potential of CNT/polymer composites still remains to be realized. A few key problems, such as how to prepare structure-controllable CNTs with high purity and consistently dependable high performance, how to break up entangled or bundled CNTs and then uniformly disperse and align them within a polymer matrix, how to improve the load transfer from matrix to CNT reinforcement, etc, still exist and need to be solved in order to realize the wide applications of these advanced composites.
关键词:
polymer composites;carbon nanotubes;mechanical properties;electrical;properties;thermal properties
Physical Review B
The electronic properties and magnetism of Ru-N clusters (N = 4, 6, 10, 13, 19, 43, and 55) are studied using the discrete-variational local-spin-density-functional method. The bond lengths in the clusters with N less than or equal to 13 are optimized, and the cluster binding energies are found to increase monotonically with the increase of cluster size. All clusters except Ru-19 are shown to have magnetic ground states. The average magnetic moments per atom for the Ru-N are found to decrease rapidly with the increase of the cluster size, although small oscillation exists. The calculated moments per atom for Ru-10 and Ru-13 clusters are in good agreement with the experimental values. Multiple magnetic solutions are explored, and double magnetic solutions an found for the icosahedral (I-h) Ru-13 cluster which is used successfully to eliminate the contradiction between the previous theory and experiment on the moment of Ru-13 cluster. The electronic structures of Ru-N clusters are calculated, and indicate that all clusters are metallic in behavior. The comparison between the Ru-55 cluster and the bulk counterpart indicates that Ru-55 has shown bulklike properties in the binding energy, magnetism, valence-bandwidth, and density of states. Based on electronic-structure results, the reactivity of Ru-6, Ru-19, and Ru-43 clusters toward H-2, N-2, and CO molecules is predicted.
关键词:
cobalt clusters;metal-clusters;binding-energy;cr clusters;dependence;symmetry;reactivity;vanadium;moments;systems
