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In the fusion environment, a complex stress field is generated in materials, which affects the evolution of radiation defects. In this study, the behaviors of radiation-induced defects under the effect of stress gradient field in tungsten are carefully simulated at the atomic scale with the molecular dynamics (MD) method. It was found that the stress gradient field affects the migration properties of interstitial defects, resulting in the energy barriers changing with the stress and stress gradient. In the axial stress gradient field, the movement of the 1/2 <111> interstitial dislocation loop is significantly accelerated, and it tends to move toward the region where the stress is concentrated. Within the time scale of the classical MD simulation, the stress gradient has little effect on the migration of vacancies. These results suggested that the stress gradient would cause interstitial defects to accumulate to the region where the stress is concentrated, thereby significantly changing the properties of the tungsten materials. [ABSTRACT FROM AUTHOR]

Tungsten (W) and W-based alloys are potential candidates for next-generation fusion reactors, which would withstand both irradiation damages and heavy heat load. In this work, we employed the molecular dynamic method to simulate the behaviors of different radiation defects under the effect of the temperature gradient field, which is induced by heat load. The rotation of the ⟨ 111 ⟩ dumbbell and habit plane of 1/2 ⟨ 111 ⟩ interstitial loops is analyzed in detail. The results show that these two behaviors are not significantly affected by the temperature gradient. Contrary to the thermal equilibrium state, temperature gradient results in the directional diffusion of ⟨ 111 ⟩ dumbbell and 1/2 ⟨ 111 ⟩ interstitial loops in tungsten from the cold to the hot region. The energy barrier is also reduced in the temperature gradient field, which accelerates the defect diffusion. These results indicate that the accumulation of radiation defects in the high-temperature region is expected in temperature gradient fields, which would lead to more severe radiation damages and degradation of materials. [ABSTRACT FROM AUTHOR]

Five groups of suspensions composed of polystyrene particles, having similar size but different effective surface charge, were adopted to investigate the effects of surface charge and volume fraction on the homogeneity of colloidal crystals through checking the difference between Dexp and Duni by reflection spectroscopy method (Dexp, Duni are the experimental and the expected value of the average nearest neighbor interparticle distance by assuming a uniform structure, respectively). We found volume fractions (ranging from 0.006 to 0.02) and structure types basically have no influence on the values of Dexp/Duni. Moreover, for crystals formed by lowly charged particles, Dexp/Duni is approximately equal to 1, implying the crystals are homogeneous. With the increase of effective surface charge, Dexp gradually deviates from Duni and the formed crystals become inhomogeneous. Our experimental observations are in accordance with the previous simulation results. Additionally, we also found Dexp/Duni initially drops quickly with increasing effective surface charge and then it tends to an asymptotic value (∼0.85), it is supposedly due to the saturation of effective charge. Our relevant computer simulations confirmed that the study scheme that using Dexp/Duni as an indicator to assess the homogeneity of crystal structure is tenable and the simulation results are consistent with experiments. [ABSTRACT FROM AUTHOR]

The stability of the (4 × 4) reconstruction is studied on SrTiO3(111) and LaTiO3(111) surfaces by scanning tunneling microscopy. While the reconstruction may effectively compensate the surface polarity, the associated large lattice distortion on SrTiO3 with relatively strong polarity has to be relaxed by extra adsorbates. Alternatively, substituting Sr by La can reduce the polarity and stabilize the clean reconstructed surface. This provides the driving force for La segregating towards the surface during the heteroepitaxy of SrTiO3 on LaTiO3-covered SrTiO3(111), and thus, the interface sharpness will be deteriorated. To improve the quality of heterointerfaces where the surface polarity of substrates tends to be increased by the epitaxial films, the growth kinetics must be optimized to play the major role. [ABSTRACT FROM AUTHOR]