Effect of particle polydispersity on the irreversible adsorption of fine particles on patterned substrates

We performed extensive Monte Carlo simulations of the irreversible adsorption of polydispersed disks inside the cells of a patterned substrate. The model captures relevant features of the irreversible adsorption of spherical colloidal particles on patterned substrates. The pattern consists of (equal) square cells, where adsorption can take place, centered at the vertices of a square lattice. Two independent, dimensionless parameters are required to control the geometry of the pattern, namely, the cell size and cell-cell distance, measured in terms of the average particle diameter. However, to describe the phase diagram, two additional dimensionless parameters, the minimum and maximum particle radii are also required. We find that the transition between any two adjacent regions of the phase diagram solely depends on the largest and smallest particle sizes, but not on the shape of the distribution function of the radii. We consider size dispersions up-to 20% of the average radius using a physically motivated truncated Gaussian-size distribution, and focus on the regime where adsorbing particles do not interact with those previously adsorbed on neighboring cells to characterize the jammed state structure. The study generalizes previous exact relations on monodisperse particles to account for size dispersion. Due to the presence of the pattern, the coverage shows a non-monotonic dependence on the cell size. The pattern also affects the radius of adsorbed particles, where one observes preferential adsorption of smaller radii particularly at high polydispersity.Comment: 9 pages, 5 figure

Mixed conduction induced by grain boundary engineering

Mixed oxygen-ion electronic conductors were prepared starting from the well-established solid lectrolyte La0.95Sr0.05Ga0.90Mg0.10O3?? (LSGM). The adopted strategy involved selective grain boundary doping with iron to form a grain boundary region with high electronic conductivity. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), impedance spectroscopy in air (around 300 ?C) and high temperature (700?800 ?C) ac conductivity measurements as a function of pO2 all suggest that this doping strategy was successful. In fact, on increasing the Fe-dopant level, Fe always concentrated along the grain boundary region (as confirmed by SEM/EDS), the total conductivity increased and each individual impedance arc decreased, in agreement with predictions based on the presence of a parallel pathway for electronic transport. Furthermore, the increase in total conductivity (?) with dopant level showed a positive log ? versus log pO2 dependence, typical of hole conductivity.371C-9F16-EBDE | Eduarda GomesN/

Grain boundary Fe-doping effects in LSGM

The electrical properties of La0.95Sr0.05Ga0.90Mg0.10O3 ? ? (LSGM) were modified by selective doping of the grain boundaries, using LaFeO3 screen-printed layers and annealing at high temperature to promote Fe diffusion into LSGM. Scanning electron microscopy (SEM) and energydispersive spectroscopy (EDS) analyses showed that iron was mainly located along the grain boundaries with the bulk grain composition almost unchanged. Impedance spectra showed a significant increase in the total conductivity for the Fe-doped samples, the effect being greater for the grain boundary contribution. The formation of a parallel pathway for electronic conduction along the grain boundaries explains these effects. Ageing of these samples at high temperature, after removal of the Fe source, showed a steady shift to the original LSGM behaviour, due to dilution of Fe throughout the samples.371C-9F16-EBDE | Eduarda GomesN/

Processing and electrical conductivity of lanthanum gallate core-shell heterostructures

The electrical properties of a lanthanum gallate solid electrolyte were modified by selectively doping the grain boundaries with Fe. This was achieved by sandwiching a La0.95Sr0.05Ga0.90Mg0.10O3-? (LSGM) dense pellet between LaFeO3 samples. Annealing at 1550?C in air for several hours promoted Fe diffusion into LSGM via the grain boundaries. Scanning electron microscopy and energy-dispersive spectroscopy analyses showed that iron was located at the grain boundary while the grain bulk preserved the LSGM composition. Impedance spectra obtained at low temperature consist of the two usual bulk and grain boundary contributions. A significant increase in total conductivity was observed for the iron-doped samples, the effect being greater for the grain boundary contribution. The total conductivity measured for the iron-containing material revealed a slight decrease with decreasing oxygen partial pressure, suggesting the onset of p-type electronic conduction. Estimates of the p-type electronic conductivity (?p) were obtained by fitting the low temperature impedance spectra to a simple equivalent circuit including one parallel electronic branch. The value for ?p in air at 300?C is 3.1?10-6 S/cm and the activation energy is 75.1 kJ/mol between 300 and 400?C.371C-9F16-EBDE | Eduarda GomesN/