Microstructure of Polymeric Electrolyte PEU LiClO_(4) Studied by Positron Spectroscopy

The positron lifetime spectra and ionic conductivity have been measured for polymeric electrolyte PEU LiClO_(4)as a function of temperature in the range of 120￣360 K and as a function of Li salt concentration at room temperature.From the temperature dependence of positron annihilation parameters,the glass transition and subtransition are observed,and the glass transition temperature T_(g)of pure PEU is determined to be 240 K.Above T_(g),the free volume hole size dramatically increases with temperature.The variations of positron annihilation parameters and ionic conductivities with respect to Li salt concentration at room temperature indicate that the Li salt mainly diffuses into the amorphous region in PEU LiClO_(4).The increase of Li salt concentration brings about an increase in the number of carried ions,and a reduction of the fractional free volume.

A Review of Studies of Polymeric Membranes by Positron Annihilation Lifetime Spectroscopy

A review is presented of studies of polymeric membranes by applying positron annihilation lifetime spectroscopy （PALS）. PALS has been used to study subnanometer-sized holes, to determine their size distribution and free-volume fractions, and to probe molecular-sized vacancies in glassy polymers. At present, PALS is believed to be a highly effective physical method for the examination of polymeric membranes.

Effect of Defects on Magnetic Properties of O^(+) -implanted AlN Films by Positron Annihilation Spectroscopy

Room-temperature ferromagnetism is observed in the O^(+)-implanted AIN films with O+doses of 5×10^(16) cm^(-2)(AIN:Osxion)and 2×10^(17) cm^(-2)(AIN:O_(2x1on)).The observed magnetic anisotropy indicates that the ferromagnetism is attributed to the intrinsic properties of O^(+) -implanted AIN films.The out-of-plane saturation magnetization(Ms)of the AIN:O5×10^(16) is about 0.68 emu/g,much higher than that of AIN:O_(2x1017),0.09 emu/g,which is due to the excessively high O^(+)dose made more O+ions occupy adjacent A1^(3+)positions in forms of antiferromagnetic coupling.Doppler broadening of positron annihilation radiation measurements demonstrate the existence of Al vacancies in the O^(+)-implanted AIN films.The first-principles calculations suggest that the ferromagnetism originates mainly from the Al vacancies.Meanwhile,the formation of divacancies or vacancy clusters by high concentrations of Al vacancies will lead to the transformation of VA-VAi coupling from ferromagnetim to antiferromagnetism,ultimately weakening the ferromagnetism of the sample.

Investigation of the effects of misch metal in RS Al-Fe-V-Si-Mm nanocrystalline alloys by PAT

The positron lifetime spectra of severalAl_(93.3-x)Fe_(4.3)V_(0.7)Si_(1.7)Mm_x (x = 0.5%, 1.0%, 3.0%, atom fraction) alloys with differentcontent of misch metal prepared by rapid solidification were measured, and the variations on theinterfacial defects with the content of misch metal were revealed by an analysis of the lifetimeresults. The interface characteristics derived from the lifetime results could be used to give asatisfactory interpretation of the dependence of mechanical properties on the content of mischmetal.

Preparation and Structural Characterization of Polystyrene-Rectorite Nanocomposites

The polystyrene/rectorite nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic rectorite. The structures and thermal properties of these hybrids have been investigated by X\|ray diffraction (XRD), fourier transform infrared (FT\|IR), positron annihilation spectroscopy (PAS) and thermal gravimetric analysis (TGA) techniques. It was found that exfoliation of rectorite in polystyrene (PS) matrix was achieved. The average free\|volume radius in the PS/clay nanocomposites is generally same as that in PS. Along with increment of rectorite contents, the interface between rectorite and polystyrene matrix increases, and the free\|volume concentration decreases obviously. And the polystyrene nanocomposites have higher thermal decomposition temperature than pure PS.

Characterization of lattice defects in metallic materials by positron annihilation spectroscopy:A review

Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron anni- hilation spectroscopy is a non-destructive technique lattice defects in solids on the atomic scale. Positron which enables characterization of open volume lifetime and Doppler broadening of annihilation photo-peak are the most common observables related to positron annihilation process. Positron lifetime spectroscopy enables to identify defects in solids and to determine their concentrations while coinci- dence measurement of Doppler broadening provides information about local chemical environment of defects. This article provides a review of the state-of-art of defect characterization in bulk metallic mate- rials by positron annihilation spectroscopy. Advanced analysis of positron annihilation data and recent developments of positron annihilation methodology are described and discussed on examples of defect studies of metallic materials. Future develonment in the field in proposed as well.

Dispersion of CoCl_2 into γ-Al_2O_3 Studied by Positron

Co^2＋/γ-Al2O3 samples were prepared by incipient wetness impregnation of γ-Al2O3 with different concentration solution of COCl2 and dried at 40 ℃. We measured the positron lifetime spectra of the samples of different Co2＋ mass fractions （0%-8.24%） heated at different temperatures （100 -500 ℃）. All lifetime spectra were resolved into four components, in which the third and the fourth components were related to the surface state of the micropores and the secondary pores of the γ-Al2O3. The experimental results showed that the Co^2＋ was mainly located in the micropores and the secondary pores near to the exterior of the support. For low Co^2＋ mass fraction samples, when the heating temperature was above 400℃, dispersal was almost finished. When the Co^2＋ mass fraction was above 5.59%, Co^2＋ and Cl were dispersed into the secondary pores in the form of multiple layers.

Structural features and thermoelectric performance of Sb- and Bi-doped Cu_(2)SnSe_(3) compounds

In this paper, a series of Sb-doped and Bi-doped Cu_(2)Sn_(1-x)M_(x)Se_(3) samples(M = Sb, Bi) are prepared by vacuum melting combined with the spark plasma sintering process. The effects of different atomic doping amounts on their properties are discussed. Structural studies indicate that all obtained samples comprise a single Cu_(2)SnSe_(3) phase. Sb and Bi atoms are experimentally demonstrated to be efficient cation dopants for increasing the transport performance. Compared with that doping on the cation site,Bi doping is much more efficient in increasing the electron concentration of the Cu_(2)SnSe_(3) system. Ultimately, a high figure of merit of 0.36 is achieved in the Cu_(2)Sn_(0.94)Sb_(0.06) Se_(3) sample at 773 K due to the enhanced power factor and lowered lattice thermal conductivity,which are 1.73 times higher than those of the pure sample.Our results provide an efficient approach to enhance thermoelectric performance via other doping atoms, which could also be applied to copper-based chalcogenide materials.

On the helium bubble swelling in nano-oxide dispersion-strengthened steels

The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.

Atmospheric CO_(2) capture and photofixation to near-unity CO by Ti^(3+)-V_(o)-Ti^(3+) sites confined in TiO_(2) ultrathin layers

To realize efficient atmospheric CO_(2) chemisorption and activation,abundant Ti^(3+) sites and oxygen vacancies in TiO_(2) ultrathin layers were designed.Positron annihilation lifetime spectroscopy and theoretical calculations first unveil each oxygen vacancy is associated with the formation of two Ti^(3+)sites,giving a Ti^(3+)-V_(o)-Ti^(3+) configuration.The Ti^(3+)-V_(o)-Ti^(3+) sites could bond with CO_(2) molecules to form a stable configuration,which converted the endoergic chemisorption step to an exoergic process,verified by in-situ Fourier-transform infrared spectra and theoretical calculations.Also,the adjacent Ti^(3+)sites not only favor CO_(2) activation into COOH*via forming a stable Ti^(3+)–C–O–Ti^(3+) configuration,but also facilitate the rate-limiting COOH^(*)scission to CO^(*)by reducing the energy barrier from 0.75 to 0.45 e V.Thus,the Ti^(3+)-V_(o)-TiO_(2) ultrathinlayers could directly capture and photofix atmospheric CO_(2) into near-unity CO,with the corresponding CO_(2)-to-CO conversion ratio of ca.20.2%.

Effects of alloying elements Mn,Mo,Ti,Si,P and C on the incubation period of void swelling in austenitic stainless steels

Void swelling,which induces the degradation of the original properties of nuclear materials under high-energy particleirradiation,is an important problem.The incubation period,a transient stage before the steady void growth,determines the duration of service of nuclear materials.Several experimental studies have been performed on void observations by transmission electron microscopy(TEM),which,however,has a resolution limit for the size of defect clusters.Positron annihilation lifetime spectroscopy(PALS)enables the detection of small vacancy clusters,single vacancies,dislocations and precipitates.The use of these two methods provides complementary information toward detecting defect information in the incubation period.Here,defect structures during the incubation period in austenitic stainless steels,by means of PALS and TEM are reviewed.The role of alloying elements into determining the period is explained.Furthermore,the existing problems and research directions in this field are presented.