Concentration Of Vacant Sites Research Articles

Ag2S/Ag heteronanostructure

An Ag2S/Ag heteronanostructure has been prepared for the first time by hydrochemical deposition. The “acanthite α-Ag2S–argentite β-Ag2S” phase transformation has been studied in situ by high-temperature X-ray diffraction and transmission electron microscopy. The crystal structure of argentite has been revealed. It has been found that the concentration of vacant sites in the metal sublattice of argentite exceeds 92%. The reversible acanthite–argentite transformation in the Ag2S/Ag heteronanostructure at the application of the external bias voltage is considered.

Monte Carlo simulation of polymer welding

Monte Carlo Modelling of random polymer chains, course grained onto a cubic F lattice, provides the ability to monitor the long range relaxation processes and the dynamic parameters of chains up to 400 units long. The model, described and verified by Haire et al. (Haire KR, Carver TJ, Windle AH. A Monte Carlo model for dense polymer systems and its interlocking with molecular dynamics simulation. Computational and Theoretical Polymer Science 2000; in press), is here applied to the study of molecular parameters in the vicinity of different types of surface and also to the process of polymer welding, whereby adhesion between two adjacent surfaces is achieved by the interpenetration of chains which are across the surface.The model demonstrates that a surface distorts the conformation of chains adjacent to it to give an oblate molecular envelope, that the concentration of vacant sites and chain ends increases near to the surface and that the density of points representing the centres of mass of the chains increases in the sub-surface regions. These results confirm earlier predictions and provide additional confidence in the model.Modelling of the welding process leads to the parameter intrinsic weld time, tw, which is the time from initial perfect contact of the surfaces to the achievement of a weld within which the chain conformation is indistinguishable from the bulk. After the initial period in which the mating surfaces roughen, the welding proceeds according to the t1/4 law predicted by reptation theory. The time to a given level of interdiffusion across the boundary is proportional to the chain length l, a comparatively weak dependence, while tw is proportional to l3, a strong dependence. This is the same dependence on length as for the relaxation time of the chain end-to-end vectors. In fact, the agreement between the relaxation time, measured on the model of the bulk, and tw is surprisingly close, at least for the monodisperse polymers investigated here.

Properties of lithium ion-conducting ceramics based on rare-earth titanates

The properties of complex oxides with perovskite structure of the Ln2/3−XM3XTiO3 type (where Ln = rare-earth element and M = Li, Na, K) have been investigated. It has been shown that lithium - containing perovskites possess cationic conductivity, with values depending on the size of conducting channels and the concentration of vacant sites in the rare-earth ion sublattice.

Interprétation dans le plan de bode de la partie inductive des diagrammes d'impédance

A theoretical study of a reaction scheme in which the reactions take place in the adsorbed phase is performed in the harmonic mode. The faradaic impedance diagram presents an inductive loop which can be interpreted by means of the Bode diagram. The shape of the impedance diagram is found to depend mainly on the variation in the concentration of vacant sites with the frequency.

The elastic behaviour of tetrahedral materials with vacant sites

As part of a study of defect tetrahedral structure compounds, the elastic constants of single crystal specimens of Hg 3Ga 2□Te 6 and HgIn 2□Te 4 have been measured between 77 K and room temperature using the pulse superposition technique. These compounds are included in the series HgTe, Hg 5In 2□Te 8, Hg 3In 2□Te 6 and HgIn 2□Te 4 and HgTe, Hg 5Ga 2□Te 8, Hg 3Ga 2□Te 6 where there is a progressive increase in the concentration of vacant sites. While the other compounds studied are cubic, HgIn 2□Te 4 has a tetragonal structure with a c a ratio of 2.0. The components of the elastic stiffness tensor of this material at 77 K are (in units of 10 11 dyne cm −2) C 11 = 4.31 C 12 = 2.54 C 44 = 2.14 C 33 = 4.47 C 13 = 2.18 C 66 = 2.41. In a cubic material C 11 = C 33, C 44 = C 66 and C 12 = C 13: the elastic behaviour of this tetragonal compound closely resembles that of a cubic material, as might be anticipated from its structure. This similarity is further illustrated by reference to the symmetry of phase velocity and Young's modulus surfaces. Examination of the elastic constants and reduced elastic constants of these compounds shows a regular trend, the elastic stiffness decreases as the number of vacant sites increases. There is an approximately linear relationship between the reduced bulk modulus and the number of sited vacancies.

Investigation of Oxidation of Copper by Use of Radioactive Cu Tracer

A very thin layer of radioactive copper was electrolytically deposited on a copper blank. The surface was then oxidized in air at 1000°C for 18 minutes, giving an oxide layer with a thickness of 1.25×10−2 cm. After quenching, successive layers of the oxide were removed chemically, and the copper activity in each layer was measured. The observed self-diffusion of radioactive copper in the oxide agrees quantitatively with a theory based on the following assumptions: (a) The oxide grows by diffusion of vacant Cu+ sites from the outer surface of the oxide inward to the metal. (b) The concentration of vacant sites as the oxygen-oxide interface is independent of the oxide thickness, and drops linearly from this constant value to zero at the metal boundary. (c) Accompanying the inward flow of vacant sites, there is a flow of positive electron holes such as to maintain electrical neutrality. (d) Self-diffusion of copper ions takes place only by motion into vacant sites. The results give a fairly direct confirmation of the theory of oxidation first suggested by Wagner.