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Sapphire single crystals grown by an improved Kyropoulos-like method are irradiated by fast neutron flux. The irradiated doses of neutron are 10(18) and 10(19)n/cm(2). The infrared transmission spectra of sapphire were studied before and after irradiation. The irradiated samples were annealed at 200, 400, 600, 800 and 1000 degrees C for 10min in ambient atmosphere. Positron annihilation studies have been carried out before and after neutron irradiation. The experimentally measured positron lifetime in the pristine specimen is 143ps. There were aluminum vacancies produced in sapphire crystals after neutron irradiation. The positron lifetime increased with the dose of neutron flux. A longer value tau(2) was found after annealing at 600 degrees C, which indicated vacancies were aggregated with each other. The second long-time component tau(2) has been found to increase with the annealing temperature. There was almost no change in peak position of the CDB spectra after neutron irradiation and isothermal annealing. The chemical environment of core in sapphire did not change greatly after neutron irradiation.

The effect of magnetic pulse treatments on Fe73.5Cu1Nb3Si13.5B9 amorphous alloy prepared by melt-spun technique is investigated. The structural defects of the treated specimens are investigated by position annihilation lifetime spectra. The results show that amorphous alloy Fe73.5Cu1Nb3Si13.5B9 have two kinds of free volume. One is Bernal vacancy-like which is characterized by less than an atomic volume, Another is void-like defect. Under the applied pulsed magnetic field, the annihilation lifetime and the relative intensity of treated specimens is decrease because the crystallization phase separate out from the amorphous matrix. The relative intensity I2 is increase because the larger free volumes appear at grain boundary of Cu and Nb enrichment area.

Using Raman spectroscopy and positron annihilation technology (PAT). we investigate the structural properties of the codoped samples by implanting boron and oxygen ions into the intrinsic diamond films (called BO series) and by implanting oxygen ions into the diamond films doped with small amounts of boron in chemical vapor deposition (called CVDBO series). It is found that after 1000 degrees C annealing, the full width at half maximum (FWHM) value of diamond peak in Raman spectrum reduces, the amount of diamond increases above 99.6% and the stress changes from compression to tension. More important the FWHM value in CVDBO series decreases by 1.6 cm(-1) after 1000 degrees C annealing, which is larger than that in the BO series with a decrease of 0.2 cm(-1), showing that the annealing prefers to more significantly reduce the defect concentration in CVDBO series. Also, the PAT measurements indicate that the S(n) value of CVDBO series is smaller than that of BO series after 800 degrees C annealing, suggesting that CVDBO series has lower defect concentrations. It is revealed that the co-doping that implanting oxygen ions into the low concentration B-doped diamond films can give a better restoration of the damaged diamond lattice by oxygen ion implantation after high temperature annealing. The intrinsic mechanism is also discussed. (C) 2008 Elsevier B.V. All rights reserved.

Threshold displacement energies for atomic displacements along some interesting directions, and formation energies of vacancy, anti-site and several symmetric interstitial atom configurations are calculated for a TiAl alloy by a molecular dynamic method using the Finnis-Sinclair many-body potentials in this paper. The results show that, the four possible octahedral configurations are unstable and the Al(Al) [110] crowdion is energetically favored in the five stable interstitial configurations. In most directions the displacement energies for Al PKA are larger than those for Ti PKA, the strength of the interaction potentials is only determinative along [110] and [100], the values of E d of the Ti atom are larger than those of the Al atom. The results also show that the displacement energy along [001] is larger than that along the [100] direction both for the Ti atom and the Al atom.

Tempered glass is widely used in building and furniture as a type of safety glass. However, spontaneous breakage of tempered glass is a serious problem known as "glass cancer" characterized by sudden and catastrophic. It is important to reduce, prevent and predict this phenomenon of spontaneous breakage of tempered glass through preparation and application. This study focused on the mechanism of spontaneous breakage of tempered glass and provided the answers on the reasons of spontaneous breakage. The critical conditions including internal and external influence factors on spontaneous breakage were discussed. It is demonstrated that the spontaneous breakage of tempered glass is caused by stress concentration in glass itself while the stress concentration may result from various particles or defects in the glass. Furthermore, local strength is defined for tempered glass which is non-linear distributed along thickness of the glass together with residual stress. The maximum of the local strength occurs at surface of tempered glass, while the lowest value is at neutral layer. The fundamental reason behind spontaneous breakage of tempered glass is that the stress concentration in the glass exceeds local strength, while impurities, such as nickel sulfide or monolithic silicon particles traditionally considered as the breakage causes, are actually indirect causes. A criterion for spontaneous breakage of tempered glass is also revealed which is useful for analysis of breakage of glass. 402 无 机 材 料 学 报 第 31卷

Various helium-containing titanium films were deposited on Si substrates by magnetron sputtering under different helium/argon (He/Ar) ambiances. Helium concentrations and corresponding depth profiles in the Ti films are obtained by elastic recoil detection analysis (ERDA). X-ray diffraction (XRD) measurements are carried out to evaluate the crystallization of the titanium films. Vacancy-type defects and their depth profiles were revealed by slow positron beam analysis (SPBA). It is found that the defect-characteristic parameter S rises with the increment of the He/Ar flow ratios. The variation of.. indicates the formation and evolution of various He-related defects, with uniform distribution into the depth around 400 nm.

Helium-containing titanium films were prepared on Si substrates with various biases applied by magnetron sputtering under stable He/Ar ambiance. Rutherford backscattering and elastic recoil detection analyses are used to measure the thickness of the He-Ti films and the helium depth profile, respectively. Experiments of x-ray diffraction and variable energy positron annihilation spectroscopy are carried out to investigate the microstructures of titanium films and the corresponding helium-related defects developed. The behavior of the implanted He, the microstructure of the He-Ti film and the formation of He-related defects all are affected by the substrate biases applied.

The thermal expansion of as-prepared and annealed silver nanowires embedded in anodic alumina membranes with different diameters was studied by in situ x-ray diffraction in the temperature range from 25to800°C. For both the as-prepared and annealed samples, the coefficients of thermal expansion have “V” shape change as the diameters increase; and the minimum values of the coefficients of thermal expansion do not correspond to the same diameters of nanowires. The collective effects of the surface tension, the limit effects of anodic alumina membrane, and the vacancies incorporated into the silver lattice were responsible for the thermal expansion.

Thermal expansion of as-prepared and annealed ordered arrays of silver nanowires embedded in anodic alumina membranes (AAMs) was studied by in situ x-ray diffraction measurement in the temperature range from 25to800°C. The axial thermal expansion coefficient (TEC) for the as-prepared nanowires is 6.35×10−9∕°C and 6.02×10−6∕°C below and above 650°C, respectively. However, the TEC of the annealed sample turns from 2.32×10−6∕°Cto12.06×10−6∕°C when the temperature is above 350°C. The collective effects of the intrinsic expansion, surface pressure, the limit effect of AAM, and the vacancies incorporated into the silver lattice were responsible for the thermal expansion.