Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Crystal growth and characterization of In23PS3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ were grown by chemical vapor transport of the elements from a charge zone maintained at 630°C. and a growth zone at 560°C. The crystals were characterized by chemical, x-ray, and densitometric techniques. $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ is structurally related to the M^IIPS₃ thiophosphides. The compound is an insulator and has an optical absorption edge of 3.1(1) e.V.     

Crystal growth and characterization of In23PSe3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3$ were grown by chemical vapor transport of the elements. The phase is structurally related to the hyposelenophosphates, M^IIPSe₃, but contains both indium atoms and vacancies on the metal ion sites. The compound shows a high electrical resistivity (>10⁸ ohm-cm) and has an optical absorption edge at 1.9 (1) e.V.     

The discharge of a I12TaSe4 cathode for lithium battery

The discharge process was investigated on a lithium battery using $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$ as cathode. The battery works as primary battery. The potential gradually decreased from 2.1V to 1.8V upto a discharging of $\text{Li}\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4\text{≈0.5}$. Then it was almost constant at 1.8V until the discharging of about 2.0. Iodine is partially removed out of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$, keeping the host TaSe₄ chain structure as it was in the first step of discharge. The new product has tetragonal crystal lattice having lattice parameters of $\text{a}\text{=9.532}\text{A}\text{?}$ and $\text{c}\text{=25.31}\text{A}\text{?}$, which is twice of c-parameter of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$.     

Photoelectrochemical study of the layered compound In23Pse3

The layered compound $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3$ is studied by photoelectrochemical technique. Two modes of transition, indirect ～ 1.55 eV, and direct ～ 1.80 eV are evidenced. An estimation of the hole diffusion length is given through the use of Gärtner model ($\text{L}\text{? 4 μ}\text{m}$). The flat band positions of the junction $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3\text{-}\text{electrolyte}$ at different pH values are determined in an electrochemical scale.     

X-ray study of the deficient perovskite La23TiO3

The A-site deficient perovskite $\text{La}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TiO}{}_3$ was synthesized under the controlled atmosphere of CO₂H₂ mixed gas at 1350°C, and the structure was investigated by the powder X-ray diffraction method. The product is slightly oxygen deficient ($\text{La}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TiO}{}_{\mathrm{3?\lambda }}$, where 0.007 ≦ λ ≦ 0.079), and the structure is dependent on λ: when λ is small, the perovskite cell is distorted to orthorhombic symmetry and the unit cell is doubled along the c′ (> b′, a′) axis, while a cubic perovskite structure is facilitated with the increase of λ. A structural model, which calls for an ordered arrangement of the A-site vacancies along the c′-axis, is proposed and its order parameter is calculated from the intensities of the superstructure lines.     

Thermoelectric power and annealing effects in NbAl2O3 cermet-type films

The effects of annealing on the structure and electrical conduction in $\text{Nb}\text{Al}{}_2\text{O}{}_3$ semiconducting films were investigated. Annealing increases the product of the density of states and the mobility near the Fermi level, and this suggests that the mobility increases because of structural changes in the alumina matrix.Thermopower measurements allowed us to evaluate the asymmetry about the Fermi level of the product Nμ.     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

Modified manjoine WOL specimen for JIc and δi tests

A procedure is presented by which a modified WOL specimen can be designed to withstand the load required to achieve a $\text{δ}{}_{\mathrm{i}}$, or $\text{J}{}_{\mathrm{Ic}}$ test for a low yield strength, high toughness material, using information from the test of a standard WOL specimen that has suffered plastic collapse of its loading arms. The $\text{K-}\text{calibration}$ for the family of geometries used is obtained from published data fitted to a 2-dimensional half-power series, and the load point and guage point compliances are obtained through a connected beam model that is calibrated from existing compliance data to imitate a WOL specimen. Prom these calibrations the $\text{J-}\text{integral}$ tensile component correction factor is evaluated and found to be applicable for this type of specimen.     

Photoelectrochimie de CdIn2S4: Caracteristiques photoelectrochimiques de CdIn2S4(n)electrolyte aqueux

The photoelectrochemical characteristics of the $\text{CdIn}{}_2\text{S}{}_4\text{(n)}\text{electrolyte}$ cell have been studied. Surface traitments enhance the short circuit current density. This phenomena has been interpreted by a decrease of the recombination of minority carriers at the electrode/electrolyte interface. The variation of open-circuit voltage up on the incident light intensity shows that the cell can be represented by the Schottky barrier model.     

Interface characteristics of GaAsAlxGa1−x As superlattices grown by MOCVD

The structure and quality of the heterointerfaces of $\text{AlAs}\text{GaAs}$ semiconductor superlattices grown by the MOCVD technique have been examined on the atomic scale using high-resolution electron microscopy lattice imaging. The interface of either GaAs grown on AlAs (Al_xGa_1?xAs) or AlAs (Al_xGa_1?xAs) grown on GaAs is atomically smooth and without defects in both cases, and the interface quality is not degraded by increasing either the layer size or the Al composition.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

121Sb nuclear magnetic resonance of a GraphiteSbCl5 intercalation compound

Graphite will react at room temperature with SbCl₅ to form a second stage, orthorhombic, intercalation compound of lattice parameters a₀ = 849 pm, b₀ = 738 pm, and c₀ = 1272 pm. ¹²¹Sb nuclear magnetic resonance (15 MHz, 23°C) in the dispersive mode reveals a signal of width 7100 Hz located at 384 ppm downfield from SbCl^?₆. Electron spin resonance (9.5 GHz, 23°C) shows an asymmetric, $\text{ca}$. 95 G wide line of Dysonian center at g = (2.0024±0.0014). These results are consistent with oxidative intercalation of graphite by SbCl₅ to form a compound containing both SbCl^?₆ and SbCl₅. Our findings are compared to work on the analogous intercalate C₁₀AsF₅ and on the “overoxidized” material formed by reaction of graphite with WF₆ and F₂.     

On the computation of mixed-mode K-factors for a dynamically propagating crack,using path-independent integrals J'k

The path-independent integral $\text{J'}{}_{\mathrm{k}}$, which has the meaning of energy release rate in elastodynamic crack-propagation, is used to numerically obtain the mixed-mode dynamic stressintensity factors for a crack propagating in a prescribed direction with a prescribed velocity. Moving isoparametric (non-singular) elements are used to model crack propagation. Even though J' is a vector integral and hence is coordinate invariant, the desirability of using specific coordinate systems to improve the accuracies of the numerical solutions for $\text{K-}\text{factors}$ is pointed out. Two procedures for extracting the mixed-mode $\text{K-}\text{factors}$ from the J' integral for a propagating crack are given. It is found that the component of J' along the crack-axis, i.e. $\text{J'}{}_1{}^0$, is always equal to or greater than the product of a crack-velocity-function and the component normal to the crack-axis, $\text{J'}{}_2{}^0$. Several examples of a slanted crack are presented to demonstrate the practical utility of the J' integral. A discussion is also presented concerning the velocity factors for dynamic $\text{K-}\text{factors}$, and energy release rate, in a finite body.     

Deformation and fracture processes during creep of 12Cr12Mo14V ferritic steel

The creep and fracture properties of $\text{1}\text{2}\text{Cr}\text{1}\text{2}\text{Mo}\text{1}\text{4}\text{V}$ ferritic steel have been determined over the stress range 125 to 362 MNm^?2 at 838 K using high precision, constant stress equipment. When the variation of the rupture life, t_f, and the secondary creep rate, $\text{?}\text{dot}{}_{\mathrm{<mtext>s</mtext>}}$, with stress, σ, was described as ${}_{\mathrm{<mtext>f</mtext>}}\text{α}\text{?}\text{dot}{}_{\mathrm{<mtext>s</mtext>}}\text{ασ}{}^{\mathrm{n}}$ a stress exponent of was recorded. Comparison with long term data then established that, at stresses below ～ 100 MNn^?2, n decreased gradually until values close to unity were obtained at stresses approaching those encountered in electricity generating plant. This decrease in stress exponent is shown to be attributable to a progressive loss of creep resistance associated with changes in carbide dispersion rather than to any change in the mechanisms by which deformation and failure occur.     

On the constitutive relations for anisotropic materials—The crystal class D6h

We consider constitutive relations of the form W(B,…, C) where W is a scalar-valued polynomial function which is invariant under the group $\text{{D}{}_{\mathrm{6h}}\text{}}$ which defines the symmetry of the crystal class $\text{D}{}_{\mathrm{6h}}$. We make no restriction as to the number or kind of quantities appearing as arguments of $\text{W}$. We list the multilinear elements of an integrity basis for functions of quantities φ, φ',…, x, y,… where φ, φ',…, x,y,… form carrier spaces for the irreducible representations Γ₁,…, Γ'₆ of $\text{{D}{}_{\mathrm{6h}}\text{}}$. The elements of an integrity basis for functions of B,…, C are readily determined once these multilinear elements are given. We give examples and tables to facilitate the use of the results obtained here and in [1].     

G̃c and R-curve fracture toughness values for aluminum alloys under plane stress conditions

The effect of specimen geometry and subcritical crack growth on the nonlinear energy fracture toughness, $\text{G}\text{?}{}_{\mathrm{c}}$, has been examined for thin, center-cracked sheets of 2024-T3 and 7075-T6 aluminum alloys. The procedure followed was to independently vary the specimen length, L, width, w, andd crack length-to-specimen width ratio and to determine the toughness both at the onset of subcritical crack growth and at the initiation of unstable fracture. Comparisons were also made with the R-curve toughness, G_R, evaluated at unstable fracture from which it was found that both $\text{G}\text{?}{}_{\mathrm{c}}$ and G_R displayed the same trend of change with geometrical variables, with $\text{G}\text{?}{}_{\mathrm{c}}$ consistently higher than G_R. When the nonlinear energy fracture toughness was evaluated at the onset of subcritical crack growth, it was found that the geometry dependence essentially disappeared.Scanning electron microscopic examination of some typical fracture surfaces showed that stable crack growth was accompanied by a gradual change of fracture mode from plane strain to plane stress. An analysis of possible errors in the experimental procedure showed that the scatter observed in $\text{G}\text{?}{}_{\mathrm{c}}$ values was not due to experimental errors, but apparently due to inhomogeneities in the materials. Several techniques were also introduced for the purpose of more directly incorporating crack growth into the $\text{G}\text{?}{}_{\mathrm{c}}$ determination, but it was found that they did not cause significant variation in the toughness values.