D.J. Li

First-Principles Calculation of Elastic Properties of TiB2 and ZrB2

Based on Density Functional Theory (DFT), using first-principles pseudopotential plane wave method, elastic properties and electronic structure of TiB2 and ZrB2 were calculated. The elastic constants of these compounds were calculated by Voigt-Reuss-Hill method. The results show that the elastic modulus of TiB2 and ZrB2 are 594 and 520 GPa, and the shear modulus are 268 and 229 GPa, respectively. Pugh empirical criterion and Poissons ratio show that the two compounds are very brittle, and the brittleness of TiB2 is higher than ZrB2. Finally, the differences in elastic properties between TiB2 and ZrB2 result form their electronic structures.

Effect of Reaction Temperature on Carbon Nanotubes

A series of the carbon nanotubes were synthesized on quartz substrates in a chemical vapor deposition (CVD) process. Ethylene was used as the carbon source, and ferrocene used as the catalyst. The scanning electron microscope (SEM) and Raman spectrum were employed to investigate the effects of reaction temperature on the structure and components of the carbon nanotubes. The results showed that, when the reaction temperature is 860°C , the best synthesis of the well-distributed carbon nanotubes with less of non-carbon impurity was achieved. At this condition, The length of the CNTs was 95 μm and the diameter was 104 nm.

Ferroelectric and Dielectric Properties of La2O3-Doped BaTiO3 Ceramics

The different concentration La2O3-doped BaTiO3 ceramics were prepared by sol-gel method. The ferroelectric and dielectric properties of the ceramics are characterized by TF analyzer 2000. With the increased amount of La2O3-doped, the dielectric constant increase gradually, when the sintering temperature is 1250 °C, the dielectric constant has reached 4648 for La2O3 with 0.4％-doped. With the temperature increased the dielectric constant of La-BaTiO3 increase gradually, when the sintering temperature is 1290 °C, the dielectric constant has reached 7066 for La2O3 with 0.4％-doped.

First-Principles Calculations of Transition Metal Nitrides TiN and NbN

First-principles study of elastic modulus, shear modulus and some other elastic parameters of TiN and NbN are reported using the plane-wave pseudopotential density functional theory method in this paper. The calculated lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The band structure and density of states of these two compounds were obtained, which show that the mainly contribution on pseudopotential calculations of the density of states of TiN is Ti-3d orbital and N-2p orbital, while TiN is the Nb-4d orbit and B-2p orbit, TiN with higher conductivity; Pugh empirical criterion shows that TiN and NbN are both brittle compounds, and NbN is more brittle than TiN.