Pressure dependence of the electrical resistivity of natural cassiterite SnO2 and of undoped and Co-doped nanocrystalline SnO2

The pressure dependence of the electrical resistivity of three different samples of cassiterite, namely natural cassiterite SnO₂, synthetic nanocrystalline SnO₂ (with crystallite size 46?nm) and nanocrystalline Co-doped SnO₂ (with crystallite size 32?nm), has been measured up to 7?GPa at room temperature. The resistivity of natural cassiterite SnO₂ decreases from 2.5?×?10⁴?Ωm at normal pressure and temperature to 1.7?×?10⁴?Ωm at 7.0?GPa. The nanocrystalline SnO₂ has a high resistivity 6.0?×?10⁵?Ωm at normal pressure and temperature and decreases with pressure reaching a value of 2.98?×?10⁵?Ωm at 7?GPa. The activation energy of the electrical conduction of the studied samples were found to be 0.32?eV for the natural SnO₂, 0.40?eV for the nanocrystalline SnO₂ sample and 0.28?eV for the nanocrystalline Co-doped SnO₂. Measurements of the pressure dependence of the electrical resistivity of the Co-doped SnO₂ showed a decrease from 3.60?×?10⁵ to 5.4?×?10⁴?Ωm at 7.0?GPa. We did not observe any pressure-induced phase transition in SnO₂ up to 7?GPa. This study of the high-pressure phase stability of cassiterite corroborates the experimental findings of SnO₂ nanoinclusions in diamonds.     

Formation of Cu precipitates and vacancy clusters in neutron-irradiated Fe–Cu alloys

Two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, were irradiated with fission neutrons at doses ranging from 4?×?10^?6 to 0.16 dpa (displacements per atom) at ～573 K to investigate the formation of Cu precipitates and microstructural evolution. The Cu content only affected the formation of Cu precipitates and microvoids at low doses. In Fe–0.3Cu, the formation of microvoids and Cu precipitates initiated at doses of 1.2?×?10^?4 and 4?×?10^?5 dpa, respectively. On the other hand, the formation of microvoids started at a dose of 4?×?10^?4 dpa in Fe–0.6Cu, and Cu precipitates were formed even after irradiation to 4?×?10^?6 dpa. On further irradiation, the difference in the formation of Cu precipitates and microvoids was small. Microvoids grew with increasing irradiation dose up to 3?×?10^?3 dpa in both alloys. Prominent aggregation of Cu atoms occurred upon irradiation from 3?×?10^?3 to 1.6?×?10^?2 dpa and the microvoids shrank. The Cu precipitates no longer grew, and microvoids nucleated and grew in the matrix above a dose of 1.6?×?10^?2 dpa in both alloys. The present studies clearly reveal the relationships between the formation and growth of Cu precipitates and microvoids with irradiation dose.     

Tensile properties of precracked tempered martensitic steel specimens tested at ultralow strain rates in high-pressure hydrogen atmosphere

Tensile tests were performed on precracked Cr–Mo martensitic steel (C: 0.38, Si: 0.22, Mn: 0.84, P: 0.024, S: 0.021, Ni: 0.08, Cr: 1.11, Mo: 0.15, Cu: 0.12, Fe: bal. (wt%)) specimens at various strain rates (ranging from 6.5 × 10^?8 s^?1 to 1.0 × 10^?4 s^?1) in high-pressure (95 MPa) hydrogen and helium atmospheres. Irrespective of the strain rate, the tensile strength in the helium atmosphere was 1400 MPa. In the hydrogen atmosphere, the tensile strength decreased to less than 600 MPa at a strain rate of 2.0 × 10^?5 s^?1. However, the tensile strength increased to 900 MPa when the strain rate was decreased to 6.5 × 10^?8 s^?1. This recovery of the tensile strength was because of the decrease in the local stress in the vicinity of the precrack because of hydrogen.     

Epifluorescence optical microscopy: a sensitive tool for determining the spatial distribution of europium-dihalide precipitates in KCl : KBr : Eu2+ crystals

The spatial distribution of europium-dihalide-type precipitates in KCl?:?KBr?:Eu²⁺ single crystals annealed at 200°C for long periods of time was determined by epifluorescence optical microscopy. Laue-type patterns and optical spectroscopy were used to test the degree of long-range ordering of the specimens and to monitor the precipitation during annealing, respectively. Precipitates smaller than about 0.08?µm were found (2.84?×?10¹² precipitates cm^?3) all across the host, whereas larger precipitates of about 0.17?µm were found (2.9?×?10⁴ precipitates cm^?1) along certain linear structural singularities of the matrix. These singularities, identified as crystal dislocations, were observed to terminate always either at a triple node of singularities or at the crystal surface, forming a three-dimensional network of crystal singularities (2.0?×?10⁶ singularities cm^?2), identified as the Frank network. The presence of europium exhaustive matrix zones accompanying the observed europium-decorated paths indicates that impurity segregation processes, occurring during annealing, favour the precipitation phenomena.     

The temperature dependence of the optical dispersion parameters in Si and Ge

Abstract

In Si and Ge, the optical dispersion parameters (single-oscillator energy E_o , dispersion energy E_d and bond energy gap E_g developed by Wemple and DiDomenico, and Phillips) have been analysed in the temperature range 100-300 K using data obtained by Icenogle et al. E_o and E_g exhibit a very small temperature dependence in both materials. The thermal coefficients of the dispersion energy, dE_d/dT, have opposite signs (Si, –41·9 × 10^?4eVK^?1; Ge, +37·7 × 10^?4eVK^?1).     

Nanomachining of nanocrystalline nickel by focused ion beam

Nanocrystalline and sub-microcrystalline samples of nickel have been machined by a focused Ga⁺ ion beam (30?keV and 187?pA) at doses of 8.92?×?10¹⁶?–?2.68?×?10¹⁸ ions/cm² and their surface topography was investigated by atomic force microscopy (AFM). Values of the root-mean-square (RMS) roughness increase with increasing ion dose. The surfaces of the nanocrystalline Ni were smoother than those of the sub-microcrystalline Ni, indicating that smoothing due to diffusion for the former works more effectively than that for the latter.     

On the ultra-high-strain rate shock deformation in copper single crystals: multiscale dislocation dynamics simulations

Multiscale dislocation dynamics plasticity (MDDP) calculations are carried out to simulate the mechanical response of copper single crystals that have undergone shock loading at high strain rates ranging from 1?×?10⁶ to 1?×?10¹⁰?s^?1. Plasticity mechanisms associated with both the activation of pre-existing dislocation sources and homogeneous nucleation of glide loops are considered. Our results show that there is a threshold strain rate of 10⁸?s^?1 at which the deformation mechanism changes from source activation to homogeneous nucleation. It is also illustrated that the pressure dependence on strain rate follows a one-fourth power law up to 10⁸?s^?1 beyond which the relationship assumes a one-half power law. The MDDP computations are in good agreement with recent experimental findings and compare well with the predictions of several dislocation-based continuum models.     

Olfactory adaptation and recovery in man as measured by two psychophysical techniques

Olfactory adaptation and recovery was investigated in man, using two psychophysical procedures: modified category scaling and threshold detection. Both procedures yielded similar qualitative information regarding loss and recovery of olfactory sensitivity as a function of time and concentration of adapting stimuli. However, quantitative differences were observed that could be partially attributed to artifacts inherent in each procedure. Often more than 50% adaptation (and recovery) occurred within the first 2 min with either test procedure. In all experiments the rate of adaptation and recovery was greater at the higher of two adapting concentrations (10 × and 20 × the detection threshold I_t). Recovery occurred more rapidly than adaptation. The usefulness of both techniques is discussed in terms of the overall problem of characterizing the olfactory adaptation and recovery process in man.     

Secondary defects induced by ion and electron irradiation of GaSb

Secondary defects induced by ion and electron irradiation up to 6?dpa (displacements per atom) at liquid-nitrogen temperature in GaSb thin films are compared. For Sn ion (60?keV) irradiation, voids were observed. However, for high-energy electron (2?MeV) irradiation, interstitial-type dislocation loops were produced. The densities of voids and interstitial-type dislocation loops were almost equivalent (8?×?10¹⁴?voids/m² and 3?×?10¹⁴?loops/m²) after irradiations at the same damage level of 6?dpa. It is concluded that the formation of voids by ion irradiation follows the creation of localised vacancy defects in cascade damage.     

Characterization of Al/n-ZnO/p-Si/Al structure with low-cost solution-grown ZnO layer

We report the fabrication of Al/n-ZnO/p-Si/Al diode structures with a flower-like ZnO layer. The average grain size, microstrain and dislocation density in the ZnO layer were determined as 25?nm, 1.55?×?10^?3 and 3.23?×?10¹³?cm^?2, respectively. From absorption spectra, the optical band gap was found to be ～3.17?eV. A red shift was attributed to non-stoichiometry arising from Zn⁺² ions substituting for oxygen vacancies. The ideality factor was determined as 1.55. The barrier height was calculated as 0.71?eV from I–V characteristics and 0.73?eV using the Norde plots.     

First principles determination of the Peierls stress of the shuffle screw dislocation in silicon

The Peierls stress of the a/2?110? screw dislocation belonging to the shuffle set is calculated for silicon using density functional theory. We have checked the effect of boundary conditions by using two models, the supercell method where one considers a periodic array of dislocations, and the cluster method where a single dislocation is embedded in a small cluster. The Peierls stress is underestimated with the supercell and overestimated with the cluster. These contributions have been calculated and the Peierls stress is determined in the range between 2.4?×?10^?2 and 2.8?×?10^?2?eV?Å^?3. When moving, the dislocation follows the {111} plane going through a low energy metastable configuration and never follows the 100 plane, which includes a higher energy metastable core configuration.     

Interpretation of the low-temperature photoconductivity in a-Si

Abstract

The paper is concerned with the interpretation of steady-state photoconductivity results on undoped a-Si at temperatures of 50K and below which lead to an essentially constant value of the (photogeneration efficiency x mobility x lifetime) product νμτ?10^?11 cm² V^?1. Measurements on p⁺-i-n⁺ junctions and Cr-i-n⁺ barriers were carried out to determine the above parameters separately: (i) steadystate reverse saturation currents gave a generation efficiency of ν? 5×10-² below 50K, suggesting that geminate recombination limits the generation process. (ii) the electron drift mobility μ_e through the tail states and the charge extracted from the absorption region of the incident light were investigated by transient experiments, these showed that μ_eτ_a is limited to about 3×10^?10cm²V^?1 at low T. The independent results account for the observed νμτ values and suggest that, contrary to the interpretation of Hoheisel, Carius and Fuhs (1984), the main contribution to the low-temperature photoconductivity arises from transport in tail states.     

Dynamic properties of an ultrafine-grained Mg–Zn–Zr alloy

The effect of ultrafine-grained structure formation in Mg–Zn–Zr alloy ZK60 on its mechanical response was investigated at strain rates ranging from quasi-static to dynamic regimes. The study demonstrated that the strength characteristics of the material rise significantly with increasing strain rate, while its ductility is reduced. These effects are particularly pronounced in the dynamic loading regime, at strain rates in the (1?5)?×?10²?s^?1 range. In the ultrafine-grained alloy ZK60, the energy absorption per unit volume, W, is enhanced by grain refinement by a factor as high as eight for the highest strain rate of 5?×?10²?s^?1 investigated. The analysis is focused on the microstructure features that bring about the observed improvement of the tensile characteristics, as well as the deformation and fracture modes prevalent at different strain rates. The results obtained contribute to the exploration and understanding of dynamic behaviour of magnesium alloys.     

Surface tension measurement of undercooled liquid Ni-based multicomponent alloys

The surface tensions of liquid ternary Ni–5%Cu–5%Fe, quaternary Ni–5%Cu–5%Fe–5%Sn and quinary Ni–5%Cu–5%Fe–5%Sn–5%Ge alloys were determined as a function of temperature by the electromagnetic levitation oscillating drop method. The maximum undercoolings obtained in the experiments are 272 (0.15T _L), 349 (0.21T _L) and 363?K (0.22T _L), respectively. For all the three alloys, the surface tension decreases linearly with the rise of temperature. The surface tension values are 1.799, 1.546 and 1.357?N/m at their liquidus temperatures of 1719, 1644 and 1641?K. Their temperature coefficients are ?4.972?×?10^–4, ?5.057?×?10^?4 and ?5.385?×?10^?4?N/m/K. It is revealed that Sn and Ge are much more efficient than Cu and Fe in reducing the surface tension of Ni-based alloys. The addition of Sn can significantly enlarge the maximum undercooling at the same experimental condition. The viscosity of the three undercooled liquid alloys was also derived from the surface tension data.     

Fractal patterns in Au–Ta multilayer films upon ion beam mixing

Metallic glass has been formed in Au₅₀Ta₅₀ multilayer films upon 200?keV xenon ion mixing at an irradiation dose of 1?×?10¹⁵?Xe⁺/cm². Electron diffraction and high-resolution transmission electron microscopy analysis confirm that the metallic glass consists of two amorphous phases, evolved from Au and Ta lattices, respectively, and also reveal the formation of a fractal morphology with a fractal dimension of 1.73?±?0.05 in the dual-phase glass features. In similar Au₆₅Ta₃₅ multilayer films, a fractal pattern is also observed at a dose of 1?×?10¹⁵?Xe⁺/cm², while the pattern, with a fractal dimension of 1.74?±?0.05, is composed in this case of a crystalline Au-based solid solution and a Ta-based amorphous phase. Interestingly, the fractal dimensions of the two irradiation-induced fractal patterns match quite well with that expected on a cluster diffusion-limited aggregation model.     

Electrical properties and local structure of n-type conducting amorphous indium sulphide

An n-type amorphous chalcogenide, In₄₉S₅₁, having a band gap of 1.9eV, has been found. The conductivity in as-prepared films was ～10^?4?S?cm^?1, which increased to 1?×?10^?1?S?cm^?1 on post-annealing at 125°C in vacuum, accompanied by a reduction in the sulphur content of the films. TEM observations showed the amorphous nature of the films before and after annealing. Both Seebeck and Hall coefficients are negative, indicating that the major carriers are electrons. The Hall mobility can be as large as 26?cm²?V^?1?s^?1 at 300?K. No significant changes to the optical absorption were observed upon annealing. Analysis of the X-ray radial distribution function reveals that the sulphur atoms have four-fold coordination, making the structure more rigid than conventional amorphous chalcogenides in which the chalcogen is alloyed to elements of group IV or V of the periodic table. We tentatively associate the electron carrier generation with the formation of sulphur vacancies.     

Cross-modal estimation of angular velocity

The exponent of 1.0 found previously for numerical magnitude estimates of angular velocity during passive rotation was validated by auditory cross-modality estimates. Acceleration intensities ranged from 3°/sec² to 24°/sec², with durations varying from 10 sec to 80 sec. It was concluded that adaptation evident in responses to the longer duration stimuli is a real phenomenon and of potential significance as one form of disorientation.     

Structural changes induced by low-energy electron irradiation in GaSb

Structural changes in GaSb (001) thin films upon low-energy electron (125?keV) irradiation have been studied by in situ transmission electron microscopy. No structural changes were observed for irradiation at room temperature. However, in a sample irradiated at 473?K domains of {110} variant, rotated 90° from each other, were formed in the matrix. The average diameter of the domains was approximately 18?nm in the sample irradiated to a fluence of 4.8?×?10²⁴?electrons/m². It is considered that the domains are pseudo-{110} planes in the matrix formed by electron-irradiation-induced Shockley partial dislocations.     

Strain rate response of a Ni–Ti shape memory alloy after hydrogen charging

In this work, we investigate the susceptibility of Ni–Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10?A/m² during 2–12?h in 0.9% NaCl solution and aged for 24?h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10^?6 to 5?×?10^?2?^?s^?1 have been achieved. After 8?h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10^?6 to 10^?4?s^?1. In contrast, no embrittlement has been detected for strain rates of 10^?3?s^?1 and higher. However, after 12?h of hydrogen charging and 24?h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni–Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.     

Potentiation of the pressor response to stress by tolbutamide in dogs

Tolbutamide has previously been shown to amplify the pressor effects of “exogenous” catecholamines in conscious dogs, possibly due to sensitization of the α₁-adrenoreceptor-mediated vasoconstriction. The objective of this study was to examine if tolbutamide also amplifies the pressor effects of “endogenous” catecholamines released during psychological stress (classical Pavlovian aversive conditioning). Experiments were conducted in β-adrenoreceptor-blocked (propranolol, 1 mg/kg, i.v.) conscious dogs (n=4) trained in classical aversive conditioning. Conditioning was accomplished by following a tone (CS+) with a 1/2 second shock; another tone (CS-) was not followed by any shock and served as control. With saline pretreatment, aversive conditioning (i.e., CS+) increased mean arterial pressure (MAP) only by approximately 4.7% when compared to CS-, whereas with tolbutamide (45 mg/kg, i.v.) pretreatment, the increase in MAP induced by CS+ beyond what was induced by the CS- (approximately 6.2%) was significantly (p<0.05) larger than that with saline pretreatment. In isolated canine femoral arterial segments (n=4), the vasoconstrictor effect of phenylephrine (an α₁-agonist) at 5×10^?6M (which was the EC₅₀ value) was amplified by 2×10^?2M of tolbutamide from 54.0±2.0% to 66.9±2.1%. In conclusion, tolbutamide amplifies the pressor effects of “endogenous” catecholamines in conscious dogs, possibly by sensitization of the α₁-adrenoreceptor-mediated vasoconstriction. This mechanism of action is novel and has not been reported with other agents.