In this work, Bi 2 Te 3 nanocrystals were synthesized via a hydrothermal method. They were treated by spark plasma sintering (SPS) at 350°C and further annealed between 350 and 500°C. The crystal structures and morphologies of these annealed Bi 2 Te 3 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) measurements. SEM observation indicates an obvious increase of particle size with increasing annealing temperature, but the grain size estimated from HRTEM observation and the broadening of X-ray diffraction lines show little change in the annealing temperature range between 350 and 500°C. Positron annihilation lifetime measurements reveal vacancy defects in all of the samples, which exist most probably in the grain boundary region. The average positron lifetime shows a monotonic decrease from 301 to 273 ps with increasing annealing temperatures up to 500°C. Detailed analysis of the positron lifetime indicates decrease of vacancy concentration after annealing. Meanwhile, the lattice thermal conductivity of the Bi 2 Te 3 nanocrystals increases with increasing annealing temperature. The electrical resistivity and Seebeck coefficient have also some changes for the annealed samples. The intimate correlation between vacancy defects and lattice thermal conductivity confirms that reduction of thermal conductivity in Bi 2 Te 3 nanocrystals is due to phonon scattering by vacancy defects rather than grain size effects.

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Chemical effect of Si+ ions on the implantation-induced defects in ZnO studied by a slow positron beam J. Appl. Phys. 113, 043506 (2013); 10.1063/1.4789010 Two-domain formation during the epitaxial growth of GaN (0001) on c-plane Al2O3 (0001) by high power impulse magnetron sputtering

Studies have been done to elucidate the velocity dependence of dynamic capillary pressure in the process of water displacing oil under constant pressure drops in hydrophilic capillaries with 0.92 μm in radius. Experimental results show that this dependence is closely correlated with the relative viscosities of the liquids involved. When the liquids are equal in viscosity, the displacement proceeds with constant rate and the dynamic capillary pressure stays almost unchanged, while it increases gradually with a increase in velocity in the case of water displacing more viscous oil, in contrast, it decreases gradually with a reduction in velocity when water displaces less viscous oil.

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