Search results for "Vacancy defect"
showing 8 items of 178 documents
Magnetic Disaccommodation in Manganese Ferrites in the Temperature Region IV
1991
The magnetic relaxation in polycrystalline, nonstoichiometric manganese ferrite samples MnxFe3−xO4 is investigated as a function of the Mn content (0 ≦ x ≦ 1). The analysis of the experimental results shows that in the temperature region IV two different relaxation processes at 285 (IV) and 220 K (IVa) can be distinguished. The process IV exhibits orientational relaxation characteristics and is composed by the superposition of two Debye processes with activation energies close to 0.75 and 0.80 eV whereas relaxation IV a could be associated with vacancy migration through the lattice, but future investigations are necessary to probe this. Es wird die magnetische Relaxation in polykristallinen…
Diffusional Relaxation in Dimer Deposition
1992
In deposition of dimers on a 1D lattice substrate, we find by analytical arguments, supported by numerical Monte Carlo simulations, that the effect of added diffusional relaxation is to allow the full, saturation coverage, 100%, for large times. This limiting coverage is approached according to the ~ 1/√t power law preceded, for fast diffusion, by the mean-field crossover regime with the intermediate ~ 1/t behavior.
Defects in oxide glasses
2005
An insight into the present understanding of point defects in the simplest and the most radiation-resistant oxide glass, glassy silicon dioxide (silica) is presented. The defects and their generation processes in glassy and α-quartz forms of silicon dioxide are significantly different. The only defect, confirmed to be similar in both materials, is oxygen vacancy. In silica, additional defects of dangling bond type are generated from precursor sites formed by strained Si-O bonds, and by modifier ions. The optical absorption spectra of silica are dominated by paramagnetic dangling bond type defects: silicon dangling bond (“E′-center”) and oxygen dangling bond (“non-bridging oxygen hole center…
Tailoring oxide properties: An impact on adsorption characteristics of molecules and metals
2014
Abstract Both density functional theory calculations and numerous experimental studies demonstrate a variety of unique features in metal supported oxide films and transition metal doped simple oxides, which are markedly different from their unmodified counterparts. This review highlights, from the computational perspective, recent literature on the properties of the above mentioned surfaces and how they adsorb and activate different species, support metal aggregates, and even catalyse reactions. The adsorption of Au atoms and clusters on metal-supported MgO films are reviewed together with the cluster׳s theoretically predicted ability to activate and dissociate O 2 at the Au–MgO(100)/Ag(100…
Positron Studies of Subsurface Zone in Titanium Created in Sliding Wear
2014
Positron annihilation studies of the subsurface zone constituted during dry sliding in pure titanium are reported. A new type of defect depth profile in this zone, which is not an exponential decay usually reported for other metals and alloys, is observed. Two layers in the subsurface zone are present in this metal. In the layer adjacent to the worn surface, the characteristic plateau of the mean positron lifetime that extends to a depth of 60–70 μm was observed. Small vacancy clusters and dislocations were recognized in this layer. At deeper zone, the mean positron lifetime decreased exponentially in the manner typical for the other metals. In this zone, vacancy clusters increase in size a…
Optical Properties of Natural and Synthetic Minerals
2015
The results of investigation of optical absorption and photoluminescence (PL) of topaz, beryl and yttrium aluminium garnet crystals doped with different concentrations of transition ions exposed to fast neutron irradiation and electron irradiation are presented. We suppose that irradiation leads to the formation of two types of complex centers: "Me2+-F+ (or F) centre" and complex centers, which consist of a cation vacancy and an impurity (iron, manganese and chromium) ion. Exchange interaction between radiation defects and impurity ions during neutron or electron irradiation gives rise to appearance of additional absorption and luminescence band broadening in investigated crystals.
Mössbauer and TEM studies of the perovskite system (1-y)La2/3 $$A$$ 1/3TiO3·yLaFeO3
1994
The microscopic nature of the Mossbauer phase analysis has been found as being particularly valuable in testing assumptions suggested by TEM results regarding the microdomain structure and the population of different lattice sites by iron ions in the perovskite system (1-y)La2/3\(A\)1/3TiO3·yLaFeO3 with 0.04<y < 0.25 (\(A\) is an A-site vacancy). This system was found to contain only Fe3+-phases which are stable under normal conditions, but moderate heating in vacuo causes a partial reduction of ferric ions to ferrous ions.
Modification of the Structure and Nano-Mechanical Properties of LiF Crystals Under Irradiation with Swift Heavy Ions
2011
The modifications of the structure and hardness of LiF crystals under high-fluence irradiation with MeV- and GeV-energy Au ions have been studied using nanoindentation and atomic force microscopy. The formation of ion-induced dislocations and bulk nanostructures consisting of grains with nanoscale dimensions (50 nm - 100 nm) has been observed. The structural modifications are accompanied by a strong ion-induced hardening which is related to dislocation impeding by assemblies of defect aggregates, dislocation loops of vacancy and interstitial types and grain boundaries. For MeV ions, the modifications are localized in a thin surface layer (few mm) where much higher density of deposited energ…