Defect agglomeration

Low-temperature oxygen ion irradiations of various elemental superconductors show a minimum in the Tc vs. dose curve, and a subsequent increase in Tc at higher doses. In Nb this decrease is attributed to the decrease in the energy gap anisotropy with the increase attributed to strain (which changes the electron-phonon coupling) resulting from defect agglomeration. 

For every chemistry, a better understanding on the degradation and fatigue mechanisms of ferroelectric materials, caused by domain wall pinning, defect agglomeration, or other effects, will... 

Order or disorder of defects is a matter of a fine balance between the configurational entropy of the defects and the exothermic enthalpy gained in association of certain point defects to form various t) es of larger defect agglomerations. Systems with relatively small defect concentrations are entropy controlled and consist of randomly distributed point defects. As concentration increases the enthalpy takes control and leads successively to formation of larger defect entities randomised associated defects or defect clusters, point defects assimilated into randomised stmcture elements of a new phase, superlattice ordering and extended defects, shear planes, and discrete intermediate phases. 

Characterization. The proper characterization of coUoids depends on the purposes for which the information is sought because the total description would be an enormous task (27). The foUowiag physical traits are among those to be considered size, shape, and morphology of the primary particles surface area number and size distribution of pores degree of crystallinity and polycrystaUinity defect concentration nature of internal and surface stresses and state of agglomeration (27). Chemical and phase composition are needed for complete characterization, including data on the purity of the bulk phase and the nature and quaHty of adsorbed surface films or impurities. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

At variance with the evaporated samples, Am and did not change much for the sol-gel ones, in spite of the difference between AE cation radii size (Fig. lb, c). It can be suggested that the sol-gel method succeeded in better introduction of Nd into a solid solution (supported by the TPD results) which also depended to a lower extent on the cation radii size match. The increase of the lattice anisotropy AO (Fig. Id) and the trend of the local strain values to decrease or remain about constant (Fig. lc) indicated that there was competition between disorder sources of different nature dispersed lattice defects and Nd3+ agglomerates. 

The third component in the triple defect is stasis of bile within the gallbladder that allows time for the cholesterol crystals to precipitate, agglomerate and... 

Avoid CMP chemistry that involves multicharged cations. Such chemicals compress the double charge layer and activate slurry agglomeration and process defectivity. Ions such as Al and Fe may initiate agglomeration and scratching at concentrations as low as lO to 10 M. 

There are certain unusual types of defects in metal systems that are noteworthy. It has been found (Taylor Doyle, 1972) that in NiAl alloys A1 atoms on the Al-rich side do not substitute on the Ni sublattice instead there are vacancies in the Ni sites. For example, at 55 at.% Al, 18% of Ni sites are vacant while the A1 sites are filled. Such vacancies determined by composition are referred to as constitutional vacancies. Other alloys have since been found to exhibit such vacancies, typical of these being NiGa and CoGA. Another rather curious aspect of defects is the formation of void lattices when metals such as Mo are irradiated with neutrons or more massive projectiles (Gleiter, 1983). Void lattices arise from agglomeration of vacancies and are akin to superlattices. Typically, neighbouring voids in Mo are separated by 200 A. An explanation for the stability of void lattices on the basis of the continuum theory of elasticity has been proposed (Stoneham, 1971 Tewary Bullough, 1972). 

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