Papers by Keyword: Vacancy-Type Defect

Abstract: To specify the effects of modulating mechanism of Gd substitution on the dielectric properties for Ca_1-xGd_xCu₃Ti₄O₁₂ system, the XRD, SEM and positron positron annihilation technique have been implemented. The results display that both grain size and vacancy-type defect concentration play important roles in controlling the dielectric properties of CaCu₃Ti₄O₁₂. The dielectric properties are improved by adding an appropriate amount of Gd additives (x=0.01) but weakened by higher Gd doping content since this is closely related to the grain size and concentration of vacancy-type defect in the samples.

Abstract: The evolution of the helium-related defect in polycrystalline tungsten was studied by Doppler Broadening Positron Annihilation Spectroscopy and Scanning Electron Microscope as functions of annealing temperature and implantation fluence. The experimental results showed that the defect type was not changed at lower annealing temperature, and the decline of S parameter manifested that the lower temperature annealing led the decrease of defect concentration. In addition there existed the same defect type with the increment of the implantation fluence, thus the rise of S parameter implied the increase of the defect concentration.

Abstract: Nanocrystalline (n-) Au shows a large internal friction accompanied with the modulus defects above ~200 K. After the creep test, the strong <111> preferred texture changed to rather random one but the mean grain size was unchanged. In situ STM observation indicated that the crystallites can independently move during the creep deformation. Quasi-two phase state composed of solid crystallites and anelastic/viscoelastic grain boundaries (GBs) is proposed to explain these characteristic mechanical properties of n-Au. Further, GBs show the glass-transition-like change at around 200 K, anelastic/viscoelastic transition at ~30 MPa and dynamical state change above ~200 MPa. The high vacancy-type-defect concentration plays an important role on stabilization of the quasi-two phase state in n-Au.