Luisa Peraldo Bicelli

Analytical characterization of electrode surface by X-ray photoelectron spectroscopy. β-PbO2-based cathode in voltage-compatible lithium cells

Lead dioxide cathodes, discharged in a lithium cell at significant points of the discharge curve, have been analysed by XPS and information obtained on the surface chemical composition has been used to elucidate the cell discharge mechanism.General and particular problems and complications arising in XPS investigations when ‘real’ samples are involved are critically outlined with obvious reference to the intrinsic difficulty in the surface analytical characterization of a mixture of lead compounds. An approach is suggested which stresses how even semiquantitative determinations could play a key role in the speciation analysis.

Intermetallic compound formed by electrodeposition of indium on antimony

Abstract Indium galvanostatic electrodeposition from aqueous solutions on antimony electrodes has been investigated together with time evolution of the deposit composition. The morphology, composition and structure of the deposit surface and cross-section have been analysed by SEM-EDS and X-ray diffraction both before and after annealing at 70, 110 and 135°C for increasing times. The results showed the formation of InSb, owing to indium diffusion into the bulk of the cathode and to the reaction with antimony. The indium diffusion coefficient in InSb between 25 and 135°C (from 0.1×10−19 to 2.6×10−19m2s−1) has been estimated from X-ray data and the values of the activation energy (30 kJ mol−1) and preexponential factor (1.8×10−15 m2 s−1) have been determined.

Formation of structural defects during non-coherent nucleation : An atomistic analysis

The mechanism of formation of the main structural defects during metal deposition has been investigated on the basis of atomistic considerations, aiming to relate quantitatively the crystallization overvoltage the dislocation density and the average grain size of the deposits. The theoretical behaviour was verified by the experimental findings on Zn electrodeposition.

Formation of structural defects during metal electrocrystallization

The mechanism of formation of the main structural defects during metal electrodeposition has been investigated by performing a thermodynamic analysis of crystal growth through non-coherent 3D nucleation when the substrate does not influence the process any more.

Influence of the structure of the electrodeposited antimony substrate on indium diffusion

Abstract The influence of the morphology and structure of antimony substrates on the diffusion and reaction process of an electrodeposited indium overlayer was investigated. The formation of the InSb intermetallic compound was studied by SEM-EDS and X-ray diffraction, at temperatures of 40, 70, 110 and 140°C. The antimony substrates, either crystalline or amorphous, were prepared by electrodeposition, the former being obtained in two different conditions, i.e. from a bath either not containing or containing the surface-active agent, Trylon B. The lowest indium diffusion coefficient was observed for the crystalline substrate prepared in the presence of the organic compound and the highest for the amorphous substrate, in spite of the higher surface roughness of the crystalline material. The values ranged from 0.35×10 −19 to 17.1×10 −19 m 2 s −1 , at 70°C. This behaviour was ascribed to the lower activation energy for In diffusion in the amorphous phase (53 instead of 65 kJ mol −1 ) which has a more open structure and lower density than the crystalline structure, due to the larger interatomic distances.

Influence of foreign particle adsorption on the formation of structural defects during noncoherent nucleation: an atomistic analysis

Abstract The influence of surface adsorption of foreign particles on the formation of the main structural defects during metal deposition was investigated, aiming to quantitatively relate the surface coverage, the dislocation density and the average grain size of the deposits. The theoretical results were verified by the experimental findings on NiP electrodeposits.

Intermetallic compounds formed by electrodeposition of indium on bismuth

Abstract Indium electrodeposition on bismuth cathodes at constant current density and room temperature gives rise to the formation of three intermetallic compounds owing to indium diffusion and reaction inside the electrode. The mechanism of this process has been investigated by scanning electron microscopy, energy-dispersive spectrometry and X-ray diffraction, analysing the morphology, composition and structure of the deposit surface and cross-section. The intermetallic compounds are In 2 Bi, In 5 Bi 3 and InBi, the latter being the unique compound at the end of the analysed time-scale (1500 h), while In 5 Bi 3 never emerged on the electrode surface.

Influence of temperature and of structure of antimony substrate on gallium diffusion into the GaSb semiconductor compound

Abstract The diffusion coefficient of Ga electrodeposits on Sb electrodeposited thin films, either amorphous or crystalline, was investigated to determine the influence of the morphology and structure of the antimony substrates on the diffusion and reaction process. The Ga/Sb bilayer was studied by SEM–EDS and X-ray diffraction before and after heating at temperatures of 50, 75 and 100°C. The formation of the GaSb semiconductor compound was particularly considered and the activation energy and frequency factor of the process was determined. At these temperatures, Ga was at least partially molten and the diffusion coefficient showed that the geometrical factor was prevailing over the structural one. For example, at 75°C, the values of the diffusion coefficient were 1.5×10 −17 and 6.3×10 −17 m 2 s −1 for the amorphous and crystalline antimony, respectively. On the contrary, at 20°C, a temperature at which Ga is in the solid state, the structural factor prevailed over the geometrical one and values were obtained lower by around three orders of magnitude. The prevailing influence at 20°C was identical to that previously observed for In diffusion into amorphous and crystalline Sb with InSb formation. The experimental results, both at low and high temperatures, are discussed also taking the behaviour of the In–Sb system into account.

Analytical characterization by X-ray photoelectron spectroscopy of quaternary chalcogenides for cathodes in lithium cells

Cdln2S2Se2 cathodes, discharged in a lithium cell at significant points of the discharge curve, have been analysed by X-ray photoelectron spectroscopy (XPS) and information on the surface chemical composition has been used to obtain a deeper knowledge of the cell discharge mechanism.XPS characterization indicated that, with an initial discharge greater than 0.3 F, the cathode surface chemistry was heavily modified, owing mainly to a topotactic reaction of electrolyte anions at the interface and, to a lesser extent, to the intercalation (and reduction) of electrolyte anions into the layered structure of the chalcogenide.On the basis of thermodynamic considerations the formation of species identified by XPS on the discharged cathodes has been tentatively explained and the results seem to reinforce the general model obtained by a previous electrochemical and X-ray diffraction investigation.

Thermodynamics of the Photocorrosion of n-ZnSe and p-ZnTe

In this paper we review the thermodynamics of the stability of n-ZnSe and p-ZnTe in aqueous environments relevant to photoelectrochemical cells: polyiodide and polychalcogenides (polysulphides, polyselenides and polytellurides). The following photoelectrochemical reactions were considered: (i) bond cleavage photoreactions, (ii) direct photooxidation (nZnSe) and direct photoreduction (p-ZnTe), (iii) oxidative (n-ZnSe) and reductive (p-ZnTe) photodecomposition, (iv) oxidative (n-ZnSe) and reductive (p-ZnTe) exchange photoreactions. Chemical chalcogen exchange reactions in the relevant electrolytes were also taken into account. It results that n-ZnSe can undergo the following degradation reactions: (i) bond cleavage photoreactions and direct photooxidation in both neutral and alkaline aqueous solutions, (ii) oxidative photodecomposition in polyiodide, polysulphide, polyselenide and polytelluride electrolytes and (iii) oxidative exchange photoreactions in polysulphide and polytelluride electrolytes, pZnTe can undergo the following degradation reactions: (i) reductive exchange photoreactions in polysulphide and polyselenide solutions and (ii) a scarcely probable bond cleavage photoreaction in polytelluride electrolytes. Corresponding author: Tel.: +39-0832-320325; Fax: +39-0832-297323; e-mail:benedetto.bozzini@unile.it