Nouveaux conducteurs ioniques caracterises par une structure a tunnels entrecroises

The ionic conductivity of pyrochlores A_1+α(Ta_1+αW_1?α)O₆ was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and $\text{5 10}{}^{\mathrm{?8}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 5.5 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{500}\text{K}\text{≤ 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T1_12+x(M_30+xW_3?x)O₉₀, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A₂M₇O₁₈ structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; $\text{3.6 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 1.4 10}{}^{\mathrm{?6}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 3.8 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The evolution ofionic conduction properties of all these compounds is discussed.     

Temperature dependence of the surface diffusion distance of bismuth atoms adsorbed on mica,carbon and silicon monoxide surfaces

The mean distance of surface diffusion of bismuth adatoms on mica, carbon and silicon monoxide surfaces has been determined at different temperatures by measurement of the instantaneous sticking coefficient and the nucleus density.The surface diffusion distance has been found to increase with decreasing temperature in accordance with the formula

$\text{X=}\text{1}\text{2}\text{a}{}_0\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{exp}\text{E}{}_{\mathrm{a}}\text{? E}{}_{\mathrm{d}}\text{2RT}$

at temperatures above 413, 373 and 383 K for mica, carbon and silicon monoxide respectively. Here X is one-half of the diffusion distance, E_a is the adsorption energy, E_d the activation energy for surface diffusion, a₀ the diffusion jump distance and v_0a and v_0d the vibrational frequencies associated with re-evaporation and with surface diffusion respectively. Below these temperatures it has been found that the temperature dependence of the diffusion distance deviates from the above formula; this can be explained by the presence of residual gas molecules adsorbed on the surfaces.From the temperature dependence of the diffusion distance, the respective values of the pre-exponential term $\text{a}{}_0\text{(}\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the difference of energies E_a?E_d have been estimated as 7.6 Å and 5.8 kcal mol^?1 for mica, 17 Å and 3.2 kcal mol^?1 for carbon and 58 Å and 1.3 kcal mol^?1 for silicon monoxide.     

Interdiffusion in the CuAu thin film system at 25°C to 250°C

Interdiffusion in the Cu-Au system has been studied in the temperature range 25–250°C using conductivity measurements and Auger in-depth composition profiles. Samples were prepared by three different methods: (1) Au was evaporated over evaporated Cu, (2) Au was electroplated over electroplated Cu and (3) Au was electroplated over wrought (bulk) Cu.The conductivity data for both the evaporated and the plated samples could be represented by $\text{ΔG}\text{G}\text{= 0.030{1?exp(?10}{}^5\text{t}\text{k}\text{)} ? (}\text{t}\text{k}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ where G is the conductance, t the time and k is an acceleration factor which is a function of temperature and thickness. Interdiffusion coefficients D? were obtained from the conductivity data by using the measured acceleration factors. These data can also be used to predict sheet conductance changes for reasonable thicknesses of Cu and Au films. Auger composition profiles were obtained by analysis beginning at the original Au-to-air interface and proceeding through the Au film into the Cu. Three distinct regions were found: (1) Cu oxide growth at the original Au surface, (2) a plateau region of a few atomic per cent Cu in the Au film and (3) a zone around the original Au-Cu interface where the Cu concentration rises to 100%. Interdiffusion coefficients were obtained from the Auger profiles based on the concentration gradient at the Au-Cu interface (region (3)).Interdiffusion coefficients obtained from $\text{ΔG}\text{G}$ and from the Auger profiles agreed within a factor of 10 for all three methods of specimen preparation. Over the range 50–250°C the interdiffusion coefficient could be represented by $\text{D}\text{= 2.9 × 10}{}^{\mathrm{?3}}\text{exp(?1.21}\text{eV}\text{kT}\text{) cm}{}^2\text{s}{}^{\mathrm{?1}}$, giving 1.3 × 10^-19 cm² s^-1 at 100°C and 6.2 × 10^-15 cm² s^-1 at 250°C. These values fall within the range of extrapolations of previously published data obtained at higher temperatures.Auger profiles from a Cu ribbon which had been Au plated and stored for 18 years at room temperature prior to analysis were used to obtain an upper limit of 2 × 10^-20 cm² s^-1 for the interdiffusion coefficient at 25°C. Subsequent measurements of D? on this sample at 150–250°C were in agreement with values obtained for the other two types of CuAu specimens. This agreement leads to the conclusion that the room temperature interdiffusion coefficient in the other two types of samples is also less than 2 × 10^-20 cm² s^-1.     

Growth,electrical and photoelectrical properties of Tl3SbS3single crystal

The growth of Tl₃SbS₃ single crystal is reported for the first time. 5×1×1 cm³ ingots are obtained by using vertical Bridgmann method with a 2°C/mm gradient and a 0.7 mm/h growth rate. Intrinsic conductivity and photoconductivity are investigated. The weak dark conductivity, $\text{～ 10}{}^{\mathrm{?10}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300° K, contrasts with a strong photosensitivity. The value of the fundamental band gap deduced from spectral dependence of the photocurrent is in rather good agreement with the value 1.61 eV obtained from temperature dependence of the dark conductivity. The Lux-Ampere characteristics can be described by I ∝ L ^α but changes in α with illumination intensity and temperature show that at least two different local centers are involved in the carrier recombination mechanism.     

ESR evidence for the existence of rutile-type,nonstoichiometric vanadium antimonate

A nonstoichiometric vanadium antimonate has been synthesized from a high temperature solid state reaction of V₂O₅ and Sb₂O₃. Powder-X-ray diffraction data of this phase could be indexed on a tetragonal basis with $\text{a}\text{= 4.60}\text{A}\text{?}$, $\text{c}\text{= 3.02}\text{A}\text{?}$. The phase exhibits a well resolved hyperfine ESR spectrum at 298 K due to V(4+)(3d′) ions interacting with ${}^{51}\text{V}\text{(}\text{I}\text{=}\text{7}\text{2}\text{)}$, thus establishing its identity as a rutile type phase postulated earlier. The ESR parameters are $\text{g}{}_{\mathrm{}}\text{= 1.933±0.002}$, g_⊥ = 1.984±0.002, $\text{A}{}_{\mathrm{}}\text{= 193±3}\text{G}$, A_⊥ = 75±3G. Present results are discussed in relation to ESR of V(4+) in other rutile-type hosts.     

Fracture toughness characterization of several aluminum alloys in semi-brittle fracture

A method has recently been developed for determining a nonlinear fracture toughness parameter defined by the relation $\text{G}\text{?}{}_{\mathrm{c}}\text{=}\text{C}\text{?}\text{G}{}_{\mathrm{c}}$ where G_c is the critical elastic strain energy rate as defined by Irwin. The $\text{C}\text{?}$ term is a function of the nonlinearity of the load-displacement test record and has been evaluated using the three parameter Ramberg-Osgood approach, although other curve fitting techniques could be applied as well. The method is quite straightforward and is applicable to plane stress, plane strain and mixed mode testing although only plane stress conditions are considered in this paper. For the case of a linear load-displacement record $\text{C}\text{?}\text{→ 1}$ and $\text{G}\text{?}{}_{\mathrm{c}}$ reduces to the linear elastic result.The toughness parameter $\text{G}\text{?}{}_{\mathrm{c}}$ has been evaluated for a number of high strength aluminum alloys and compared with published G_c values for these materials. The tests were conducted on center-cracked sheets of 2014-T6, 2024-T81, 7075-T6 and 7475-T61 aluminum alloys under conditions of varying specimen geometry and displacement gage length. It was found that the values of $\text{G}\text{?}{}_{\mathrm{c}}$ obtained from displacement readings with a gage length of 2 in. generally agreed with published values of $\text{G}{}_{\mathrm{c}}\text{=}\text{K}{}_{\mathrm{c}}{}^2\text{E}$. The $\text{G}\text{?}{}_{\mathrm{c}}$ values were found to vary inversely with gage length and a/w ratios. The variation in values for $\text{G}\text{?}{}_{\mathrm{c}}$ is of the same order of magnitude as the scatter in published values for G_c. However, $\text{G}\text{?}{}_{\mathrm{c}}$ appears to be less sensitive than G_c to changes in a/w.     

A thin film electrochromic display based on the tungsten bronzes

The main features of a passive thin film display cell based on the electrochemically reversible formation of a tungsten bronze according to the reaction

$\text{(colourless) WO}{}_3\text{+ x}\text{M}{}^{\mathrm{+}}\text{+ x}\text{e}{}^{\mathrm{?}}\text{?}\text{M}{}_{\mathrm{x}}\text{WO}{}_3\text{(blue)}$

where 0 < x < 1 are considered. Chemical analysis of an electrochemically coloured WO₃ film has confirmed the presence of M. It is shown that a critical requirement of these cells is that D_τ(qC_m/Q)² ≈ 1, where the symbols are, in order, the M⁺ diffusion coefficient, the required device response time, the electronic charge, the maximum practical volume concentration of M in the WO₃ film and lastly the area colouring charge. Typical energy requirements might be about 10 mJ cm^?2 per complete cycle in a favourable case.Ionic injection overpotentials and ionic diffusion both appear to play a significant role in determining cell currents. Preliminary diffusion coefficient results for Li⁺ in r.f. sputtered WO₃ films are reported, and their predicted dependence of film structure is discussed. The optical absorption of coloured WO₃ films is presented, and it is interpreted as being predominantly due to free-electron intraband transitions.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.     

Coupling losses of finite superconducting cables

The calculations of coupling losses in superconducting cables are generalized for ac fields with time variations comparable with, or even larger than, the time cosntant τ of the coupling currents. The losses are calculated as function of the frequency ω and the cable length. At small frequencies, the losses are a monotonically increasing function of the cabling length, whereas for larger frequencies the losses reach a maximum at lengths about l₀/(1 + ωτ) (l₀ is the cabling length) and then they decrease with further increase of the length. Moreover, for systems with larger values of V = $\text{2 π}{}^2\text{(R + D)}{}^2\text{l>}{}_0{}^2$ (R is radius of the strand, D is the distance between them) the oscillations dependent on the cable length are more pronounced. For a given cable length, three characteristic forms of the frequency dependence of losses are found.The results can be important when comparing the losses from measurements on finite samples with the expected losses in larger systems (eg magnets for fusion reactors, generators, etc.).     

Interpretation of the solution to the inverse problem for the positive function and the reconstruction of neutron spectra

The present paper treats the problem of reconstruction of a positive function S(E > 0) from its measured functionals $\text{Y}{}_{\mathrm{n}}\text{= ?}\text{d}\text{EA}{}_{\mathrm{n}}\text{(E)S(E)}$. The reconstruction method is based on the Tikhonov's regularization of the problem as well as on the priori information that S(E) is positive. In detail are considered the statistical properties of the reconstructed function $\text{S}\text{?}\text{(E)}$.     

Studies in convergence of stochastic models in rough-surface hydrodynamic lubrication theory

The stochastic Reynolds equation for hydrodynamic lubrication with random homogeneous roughness of the lubricated surface is studied using series expansions. In the case in which the roughness function $\text{δ ? C}{}^0\text{(}\text{}\text{?}\text{gW)}$, we show convergence of the series for pressure and its expectation in the Sobolev space $\text{H}{}^1\text{(Ω)}$, whereas in the case in which $\text{δ ? C}{}^1\text{(}\text{}\text{?}\text{gW)}$, the series converge in $\text{C}{}^2\text{(Ω)}$ provided ▽δ is uniformly bounded.     

Effect of texture and grain structure on electromigration in Al-0.5%Cu thin films

The electromigration resistance of Al-0.5%Cu meander lines was found to increase with increasing grain size s and degree of {111} preferred orientation and with decreasing spread σ in the grain size distribution. This dependence on microstructure can be expressed in terms of the empirical quantity $\text{(}\text{s}\text{σ}{}^2\text{)}\text{log}\text{(}\text{I}{}_{111}\text{I}{}_{200}\text{)}{}^3$ which correlates well with the electromigration lifetime of films obtained by different deposition techniques.     

Thermonuclear fusion neutrons under “Currentless plasmas” in Heliotron E

Thermonuclear fusion neutron emissions of up to 3 × 10⁹ neutrons/s have been observed in Heliotron E deuterium plasmas. “Currentless plasmas” were produced by electron cyclotron resonance (53 GHz, 150 kW) and further heated by hydrogen neutral beam injection (2.2 MW, H⁰→D⁺). It is found that all observed neutron emissions have thermonuclear origin due to the absence of hard X-ray background. Agreement between neutron and charge exchange ion temperature measurements (500 eV < T_i(0) × 900 eV) have been found at intermediate densities $\text{(1.5 ×}\text{n}{}_{\mathrm{<mtext>e</mtext>}}\text{× 3 × 10}{}^{13}\text{cm}{}^{\mathrm{?3}}\text{)}$. The neutrons reported in this paper are the first observations of pure thermonuclear fusion neutrons in a helical heliotron plasma confinement device.     

Flux-pinning by superconductor-normal boundaries

It is shown that flux-pinning by Nb₃Sn-Cu interfaces in in-situ superconducting composites can lead to a pinning function of the form $\text{F}{}_{\mathrm{p}}\text{∝ b}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1 ? b)}{}^2$, as is found experimentally.     

Electrical properties of electrochemically prepared thin polytetrahydrofuran films I: Characterization under A.C. conditions

The electrical characteristics of platinum-polytetrahydrofuran (poly-THF)- gold capacitors were studied under a.c. conditions at temperatures between 173 and 353 K and at frequencies between 10² and 10⁶ Hz. When the temperature T is 300 K the capacitance C and the loss tangent tan δ are constant in the frequency range 10²-10⁵ Hz; when ? is greater than 10⁵ Hz the capacitance decreases slightly and the loss tangent increases rapidly from 2 x 10^?2 to 0.17. In the range 10⁴?5x 10³ Hz the imaginary part ε″ of the dielectric constant has two loss peaks which are related to phase changes: one at 243 K corresponding to the glass transition point T_g(U) of the crystalline phase of the poly-THF (itself a semicrystalline polymer) and one at 203 K corresponding to the glass transition point T_g(L) of the amorphous phase. When T is greater than 319 K the loss tangent increases rapidly at very low frequencies $\text{(10}{}^2\text{Hz}\text{<?<10}{}^3\text{Hz}\text{)}$; 319 K corresponds to the melting point T_αC of the crystalline phase.The average dielectric constant is 3.8, a value which is of the same order of magnitude as that of bulk poly-THF. The activation energy of the dielectric is 0.002 eV in the temperature range 173–250 K and is 0.03 eV at higher temperatures. The conduction mechanism for the capacitors studied in this work is of the hopping variety, as shown by the variations of the conductance G with T and ?; G is proportional to $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ at a given frequency, and G is ?ⁿ dependent where n is 0.85 at low frequencies and low temperatures and where n is 2 at high frequencies regardless of the temperature.     

Crack tip closure and environmental crack propagation

Crack propagation rate, da/dN, and crack tip closure stress, σ_cc, in part-through crack fatigue specimens of aluminum alloys are drastically affected by gaseous environments. The present studies indicate that the crack closure reflects the influence of the environment on the plastic deformation at the crack tip, and, therefore, on the crack propagation rates. Postulating that da/dN is mainly determined by $\text{ΔK}{}_{\mathrm{eff}}\text{∝ (σ}{}_{\max }\text{?σ}{}_{\mathrm{cc}}\text{)}$ (instead of $\text{ΔK ∝ (σ}{}_{\max }\text{?σ}{}_{\min }\text{)}$, as is done traditionally) leads to the relationship $\text{da/dN = A(ΔK}{}_{\mathrm{eff}}\text{)}{}^{\mathrm{n}}$ in which $\text{A}$ and $\text{n}$ are virtually independent of the gaseous environment. The exponents are $\text{n ≈ 3.3}$ for Al 7075 T651 and $\text{n ≈ 3.1}$ for Al 2024 T351, respectively.     

Optical absorption and photoconductovity in amorphous indium selenide thin films

Optical absorption coefficient and photoconductivity measurements were performed on amorphous indium selenide thin films produced by vacuum evaporation. The dependence of the absorption coefficient α on the photon energy ħω at the edge of the absorption band is well described by the relation $\text{α}\text{h}\text{̵}\text{ω = B(}\text{h}\text{̵}\text{ω - E}{}_{\mathrm{<mtext>opt</mtext>}}\text{)}{}^2$ where B is a quality factor and E_opt is the optical band gap. The steady state photoconductivity as a function of the temperature and light intensity is tentatively interpreted in terms of a simple kinetic model proposed by Weiser et al.     

Some d.c. properties of evaporated thin aluminium fluoride films

The measurements of some d.c. properties of samples of evaporated aluminium fluoride thin films sandwiched between metal electrodes are reported. The technique of Rutherford scattering of megaelectronvolt alpha particles was used to study the stoichiometry and impurity content of the films. Measurements were made in the temperature range 77–393 K, and the thickness of the films ranged from 800 to 4000 Å. At high temperatures and high fields the conduction process can be explained on the basis of the Poole-Frenkel mechanism in amorphous materials, as described by Hill. At low temperatures the conductivity fits the Mott relation $\text{σ ∝ exp(-T}{}_0\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$. The breakdown electric field, measured as a function of film thickness d in the range 700–7500 Å, obeys the Forlani-Minnaja relation.     

The elastic interaction between solute atoms and stress field at the tip of cracks and notches

As for a mechanical interaction between a general stress singularity and an-environmental factor (e.g. hydrogen) which has influence on delayed failure characteristics of materials, it has not hitherto been analysed, although it is an important problem. In the present article an analytical basis is given for the problem of elastic interaction between solute atom as an environmental factor accelerating delayed failure and stress field around a crack and further a general V-shaped notch.The result of analysis shows that the number of solute atoms which accumulate to crack tip due to elastic interaction is proportional to a parameter. $\text{ρ}{}_0\text{(}\text{DKt}\text{kT}\text{)}{}^{\mathrm{<mtext>4</mtext><mtext>5</mtext>}}$ where K is stress intensity factor,ρ₀ initial uniform density of the solute atom, D diffusion constant, t time, k Boltzman's constant and T absolute temperature. It is further shown that the abovementioned parameter is generalized to $\text{ρ}{}_0\text{(}\text{Dkt}\text{kT}\text{)}{}^{\mathrm{<mtext>2</mtext><mtext>(2+q)</mtext>}}$ for the number of what accumulate to the apex of a general V-shaped notch due to elastic interaction where k is a factor representing a stress singularity of the notch apex and q is a constant related to apex angle a.The above analysis indicates that it is possible to describe development of delayed failure in terms of a parametre of fracture mechanics K, when viewed from a standpoint inclusive of diffusion and mechanical processes, since it is shown that the rate of concentration to crack tip of solute atoms as an environmental factor is uniquely determined by a factor $\text{ρ}{}_0\text{(}\text{DK}\text{kT}\text{)}{}^{\mathrm{<mtext>4</mtext><mtext>5</mtext>}}$.