Composition dependence of the ionic diffusion coefficients in yttria-stabilized zirconias

The diffusion coefficient of the O²⁻ ions in yttria-stabilized zirconia (1−x)ZrO₂·xYO_1.5 has been investigated as a function of the concentration of Y³⁺ ion over a range x = 0.131–0.261 by using quasielastic light scattering. The diffusion coefficients were deduced from the analysis of the temperature dependence of the scattering intensity at 3 GHz. It is concluded that the diffusion coefficient reaches its maximum value at x = 0.165. The composition dependence of the scattering intensity suggests that the concentration of the moving carrier decreases as the Y³⁺ content increases in spite of an increase of the oxygen vacancies.     

Radiation-enhanced diffusion of boron in germanium during ion implantation

An effect of radiation-enhanced diffusion during boron ion implantation into 200-500°C germanium substrates has been found. The boron-enhanced diffusion coefficient is independent of the temperature over the range 200-500°C during ion implantation, depends upon the dose rate of the incident ions and its value corresponds to the thermal diffusion of boron in germanium at 800°C.     

A demonstration of the diffusion of sodium in a glass-gas discharge system

A demonstration is proposed of the nonstationary diffusion of sodium from a melt of its salt in two-electrode light indicators of a discharge in the cases of electric fields accelerating and damping the motion of ions.Mordovinian Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 98–102, May, 1992.     

New results on diffusion in fcc metals

The Kondo model for the diffusion of light particles in metals has provided a satisfactory explanation for the low temperature diffusion rates for muons in the fcc metals Cu and Al. Explicit experiments which show the strong dependence of muon behaviour on the presence of conduction electrons have now been performed belowT=1 K in Al. Challenging new diffusion studies on fcc metals such as Pt are also presented.     

Observation of diffusion through ion irradiated Makrofol KG

The features of the latent track in polycarbonate can be analysed by measuring the diffusion constant under ultra high vacuum conditions. Stacks of 30 μm Makrofol KG foils were irradiated with uranium ions of 11.4 MeV/u at the GSI Darmstadt, Germany. We used different fluences from 3·10¹⁰ to 5·10¹¹ ions/cm². The diffusion constant was determined by the time-lag-method [1]. A quadrupole mass filter was used to observe the diffusion of the gas. We measured the diffusion of argon through different foils of each stack at room temperature. In all cases also unirradiated foils were measured. The dependence of the permeability and the diffusion constant on the ion fluence and the energy loss of the ions will be given and indications on the size of latent ion tracks concerning gas diffusion will be discussed.     

Proton diffusion in proton conducting oxides

Quasielastic neutron scattering was used to study the atomistic proton diffusion mechanism in Yb-doped SrCeO₃, a proton conducting perovskite, simultaneously in space and time. Proton diffusion consists of a sequence of trapping and free diffusion events. The free diffusion corresponds to the Grotthus mechanism including very fast rotations around oxygen ions.     

Influence of atomic to molecular conversion on the diffusion of ions

An analytical relation which describes the diffusion of positive ions is derived taking into account the process of conversion of atomic ions into molecular ions. The theoretically obtained results can be used for the interpretation of free diffusion measurements, and also for the derivation of the reaction rate coefficient from these measurements.     

Tracer impurity diffusion in single-crystal rutile (TiO2−x)

By means of the radioactive-tracer sectioning technique, the tracer diffusion of the impurity ions, ⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Co, ⁶³Ni and ⁹⁵Zr, in rutile single crystals was measured as functions of crystal orientation, temperature, oxygen partial pressure and Al impurity content. The diffusion coefficients are very sensitive to the electric charge of the impurity ions. Divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO₂, compared to cation self-diffusion, and exhibit an extreme anisotropy in diffusion behavior, divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. Trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) diffuse similar to cation self-diffusion, both as functions of temperature and oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffuse both as divalent and as trivalent ions. The impurity diffusion as functions of oxygen partial pressure and Al-impurity content are consistent with calculations of point-defect concentrations in rutile.     

On the substructure of diffusion zone in copper-alpha brass diffusion couple

The diffusion zone of a sample in the form of three layers was studied by electron microscopy, X-ray diffraction, light microscopy and microhardness test. Experimental results clearly show that in the diffusion zone there is a superposition of thermal stress and a stress due to the vacancies.     

Radiation-enhanced diffusion in ion-implanted glass

The Rutherford backscattering technique was used to characterize the purposedly added cesium impurities in soda-lime glass. The impurities were introduced into the glass matrix by an ion-exchange diffusion process at room temperature. The diffusion coefficient of cesium was determined from the measured depth profiles. The diffusion of the cesium impurities stimulated by 280 keV Kr⁺-ion beam irradiation was also studied. The depth distributions obtained are discussed using the model of radiation enhanced diffusion. Results are compared with theoretical values based on transport of ions in matter calculations and other experimental work.On sabbatical leave at Applied Science University, Physics Department, P. O. Box 926296, Amman, Jordan     

Time evolution of diffusion fringes in the Christiansen effect

When laser radiation is allowed to fall at the diffusion region separating two liquids in a Christiansen filter, a new fringe pattern appears. We termed it as “diffusion fringes”. In the present work, we have studied this interference fringe pattern and its time evolution. It has been observed that there is a definite co-relation between the shape of the fringe pattern and the width of the diffusion region. The time evolution of this fringe patterns indicates that as diffusion region increases the circular fringe becomes elliptical and finally straight. It is believed that a detailed investigation of these diffusion fringes will throw much needed light not only on the theory of the Christiansen effect but also on the rate of diffusion between two molecules.     

Anomalous diffusion and memory effects on the impedance spectroscopy for finite-length situations

The contribution of ions to the electrical impedance of an electrolytic cell limited by perfect blocking electrodes is determined by considering the role of the anomalous diffusion process and memory effects. Analytical solutions for fractional diffusion equations together with Poisson's equation relating the effective electric field to the net charge density are found. This procedure allows the construction of general expressions for the electrochemical impedance satisfying the Kramers-Kronig relations when the diffusion of ions in the cell is characterized by the usual, as well as by anomalous, behavior.     

Observation of multiple peaking and a possible enhanced diffusion effect in channelling angular distributions

Multiple peaking has been observed in a channelling angular distribution obtained with N ions back-scattered from a Br-implanted Fe single crystal. An effect associated with the same distribution is seen which is attributed to the enhanced diffusion of N in Fe.     

Temperature effects on the diffusion of water and monovalent counterions in the hydrated montmorillonite

We investigate here the effect of temperature on the diffusion of water and cations in the Wyoming-type montmorillonite clay. The considered cations are monovalent compensating ions, such as Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ in one-, two- and three-hydration states. For this purpose, molecular dynamics simulations have been performed to obtain the dynamic behaviour regarding the interlayer ions and water molecules under a temperature range between 260 and 400 K. The diffusion coefficient of water and cations in different hydrated clays increases with temperature. The influence of temperature on the diffusion of water is much greater than that of cations in one-, two- or three-hydrated clay. The degree of hydration plays an important role on the diffusion behaviour of water and counterions. We found that the effect of temperature is negligible in weakly hydrated clay, whereas it became significant in highly hydrated one. Besides, the size and mass of cations’ hydrate also affect the diffusion behaviour of water and cations in the interlayer space of hydrated clay.     

Modeling of ionic diffusion by space charge depolarization

For the study of transport properties of a nano-composite material, an open circuit condition of current is considered, where the sum of diffusion current density, displacement current density, ohmic current density, and excess charge current density is vanished. Including the effects of drift and trapping of ions, drift and trapping diffusion coefficients are modeled respectively and the significance of the type of ionic motion in the study of ionic diffusion is discussed.     

Silver-tracer diffusion in Cu2O

The diffusion of¹¹⁰Ag in Cu₂O has been measured by a serial-sectioning technique as a function of temperature (700–1132°C) and oxygen partial pressure (6 × 10^?6 ?8 × 10^?2 atm). The data are fit to the defect model for Cu₂O developed by the authors in the preceding paper. Silver ions have a larger impurity-vacancy binding free energy and/or a larger jump frequency for the singly charged cation vacancies relative to that for the neutral cation vacancies. The activation enthalpies for the diffusion of copper and silver ions in Cu₂O are nearly equal, but the absolute value of D¹_Ag is about three times larger than D¹_Cu even though the silver ion is 31% larger than the copper ion.