The microstructure and fracture properties of MgO crystals containing a dispersed phase

MgO crystals containing up to 40% by volume of magnesioferrite and up to 2% by volume of iron and nickel were produced by a diffusion technique followed by appropriate heat treatments. Magnesioferrite precipitate did not significantly change the effective surface energy of a crack as measured by the double cantilever beam technique. Iron and nickel precipitate was produced in the form of platelets lying on {100}_MgO planes whose orientation relationships were [001]_MgO ∥[001]_Fe, [110]MgO ∥[100]_Fe with a spread of +10°, approximately, and [001]_MgO ∥[001]_Ni, [010]_MgO ∥[010]_Ni with negligible spread. Despite the crystallographic orientation relationships, the metal-MgO interface appeared to be very weak; the reasons for this are discussed. The effect of the metal precipitate on crack propagation was to markedly increase the density of cleavage steps. For a volume fraction of precipitate of 0.02, this led to a small increase in the effective surface energy, on the order of 1 Jm⁻².     

Condensation and epitaxial growth of K on W(001)

The growth of K layers on W(001) from the first adsorption phases up to the deposition of thick films has been investigated by means of a RHEED camera, in the temperature range 143 ? T ? 273 K. At first the deposited potassium atoms form a W(001)-c(2 × 2)K⁺ structure, upon which a non-ionized but polarized adstructure grows. Further condensation is characterized by a very low binding energy of 0.09 eV to the substrate layer and consequently by a low condensation coefficient. The transition layer grows out of single adsorption events without the formation of nuclei, while the epitaxial layers growing upon it are initiated by three-dimensional nucleation. For these layers, epitaxial orientations $\text{K}\text{(001)}\text{W}\text{(001)}\text{with}\text{K}\text{[001]}\text{W}\text{[010]}$ or $\text{K}\text{[001]}\text{W}\text{[100]}$ were observed.     

HRTEM observation of the monoclinic-to-tetragonal m-t) phase transition in nanocrystalline ZrO2

The orientation relations m(100) || t(001), m[001] || t[110]; m(011) || t(100), m[100] || t[001]; m(100) || t(110), m[001] || t[001]; m(013) || t(116), m[001] || t[001] (indices for the primitive tetragonal cell) have been found between the tetragonal (t) and monoclinic (m) domains during the electron irradiation-induced m-t phase transition observed in-situ with HREM within isolated zirconia nanoparticles. Geometric models of the m-t interfaces are proposed.     

Microstructure of Epitaxial La0.7Ca0.3MnO3 Thin Films Deposited by Direct Current Magnetron Sputtering on LaAlO3 Substrate

Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La_0.7Ca_0.3MnO₃ films on (001) LaAlO₃ substrates prepared by direct current magnetron sputtering technique. The as-grown thin films with different thickness are perfectly coherent with the substrates. The film suffers a tetragonal deformation in the area near the interface between the film and the substrate. With increasing thickness, the film is partially relaxed. It was found that La_0.7Ca_0.3MnO₃ films consist of two types of oriented domains described as: (1) (110)_f [001]_f||(001)_s[100]_s and (1¹10)_f [001]_f||(001)_s[100]_s and (2) (110)_f [001]_f||(001)_s[010]_s and (1¹10)_f [001]_f//(001)_s[010]_s. Upon annealing, the film is relaxed by the formation of mis¯t dislocations. Other than mis¯t dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.     

Growth and structural investigations of epitaxial hexagonal YMnO3 thin films deposited on wurtzite GaN(001) substrates

Epitaxial hexagonal YMnO₃ (h-YMnO₃) films having sharp (00l) X-ray diffraction peaks were grown above 700 °C in 5 mTorr O₂ via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO₃ film and w-GaN substrate. The epitaxial relationships of the h-YMnO₃ films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001)_YMnO3 ‖ (001)_GaN : [11¯0]_YMnO3 ‖ [110]_GaN; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned.     

Point-Contact Spectroscopy of the Borocarbide Superconductor YNi2B2C in the Normal and Superconducting State

Point-contact (PC) spectroscopy measurements of YNi₂B₂C single crystals in the normal and superconducting (SC) state (T _c ≃ 15.4 K) for the main crystallographic directions are reported. The PC study reveals the electron–phonon interaction (EPI) spectral function with dominant phonon maximum around 12 meV and further weak structures (hump or kink) at higher energy at about 50 meV. No “soft” modes below 12 meV are resolved in the normal state. The PC EPI spectra are qualitatively similar for the different directions. Contrary, directional study of the SC gap results in Δ_{[100] ≈ 1.5 meV for the a direction and Δ_{[001] ≈ 2.3 meV along the c axis; however the critical temperature T _c in PC in all cases is near to that in the bulk sample. The value 2Δ_[001]/k _B T _c ≈ 3.6 is close to the BCS value of 3.52, and the temperature dependence Δ_[001](T) is BCS-like, while the for small gap Δ_[100](T) is below BCS behavior at T > T _c /2 similarly as in the two-gap superconductor MgB₂. It is supposed that the directional variation Δ can be attributed to a multiband nature of the SC state in YNi₂B₂C.     

Isovalent Substitution and Heat Treatments Control of T c, Chain Oxygen Disorder and Structural Phase Transition in High T c Superconductors (Y1−x Nd x )SrBaCu3O6+z

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in (Y_1?x Nd _x )SrBaCu₃O_6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] heat treatment increases the orthorhombicity ε=(b?a)/(b+a) (for 0≤x<1), T _c (for x>0.2) and the distance d[Cu(1)–(Sr/Ba)] (decrease T _c) for x<0.25 and decrease it (increase T _c) for x>0.25. When x increase from 0 to 1, ε decreases to 0 with transition from orthorhombic to tetragonal structure. ε[O] decreases with T _c[O]. However, T _c[AO] decreases with ε[AO] until x=0.2, increases for x=0.4 and after it decreases by 9.8 K to 77.2 K for x=1 [AO]. Remarkable correlations were observed between T _c(x) and the volume of the unit cell V(x); and between δT _c(x)=T _c[AO]?T _c[O] and δε(x). A combination of several factors such as decrease in d[Cu(1)–(Sr/Ba)]; increase in cationic and chain oxygen ordering; the number p _sh(x) of holes by Cu(2)–O₂ superconducting plans and in-phase purity for the [AO] samples may account for the observed data.     

Low-angle tilt boundaries and inhomogeneous current densities in sodium beta alumina

Observation of [h k.0] low-angle tilt boundaries in sodium beta alumina is reported. The boundaries have a habit plane close to the (00.1) planes, and are evidence for the existence of dislocations with a Burgers vector component in the [00.1] direction. The indications are that these dislocations dissociate according toc ₀[00.1]1/2c ₀[00.1]+1/2c ₀[00.1].Such tilt boundaries can cause micro-inhomogeneities in sodium ion current flow and both enhancement and decrease of conduction plane current density seems possible.     

Microstructure of a-plane ZnO grown on LaAlO3 (001)

The microstructure of a-plane ZnO grown on LaAlO₃ (LAO) (001) has been systematically investigated by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on the results of XRD and TEM, only a-plane ZnO has been found to grow on LAO (001), and it consists of two types of domains perpendicular to each other. The crystal orientation relationships of a-plane ZnO domains with LAO have been verified to be [0001]_ZnO//[110]_LAO and [11?00]_ZnO//[11?0]_LAO. The domain boundaries in the a-plane ZnO are along the direction in a rotation angle of about 45° from the c-axes of ZnO. The surface morphology of ZnO films in SEM exhibits domain structure in stripe-like shape. The formation of two domains can be attributed to the cubic symmetry of the surface configuration of LAO (001).     

A 500-J nuclear-pumped gas laser

A 500-J pulsed gas laser (laser module) pumped by uranium nuclear fission products has been created, which operates on xenon 5d[3/2]₁ → 6p[3/2]₁ transition with a wavelength of 2.03 μm. Experiments have been performed on a BARS-5 + RUN-2 complex comprising a fast aperiodic self-quenching reactor and a neutron multiplier reactor. A specific laser radiation energy in experiments achieved ～32 J/dm³ at an efficiency of 3% (ratio of the laser output pulse energy and the energy transferred from fission fragments to gas medium).     

Thioether crown complexes as templates for the assembly of extended polyiodide networks: synthesis and structures of {[M([16]aneS4)]2I}I11 (M = Pd,Pt), [Pd(cis-HO)2[14]aneS4)](I3)2, [Pd([9]aneS3)2](Ix)2 (x = 3, 5)

Pd(II) and Pt(II) complexes of [16]aneS₄ and Pd(II) complexes of cis-(HO)₂[14]aneS₄ and [9]aneS₃ have been used as templates for the self-assembly of polyiodide ions. The complexes {[M([16]aneS₄)]₂I}I₁₁ (M = Pd, Pt), [Pd(cis-(HO)₂[14]aneS₄)](I₃)₂, [Pd([9]aneS₃)₂](I_x)₂ (x = 3, 5) have been synthesized and structurally characterized. In {[M([16]aneS₄)]₂I}I₁₁, the polyiodide network consists of fused 14-member polyanion rings made up of interacting “L”-shaped I₅⁻ and I⁻ units; binuclear [([16]aneS₄)M–I–M([16]aneS₄)]³⁺ complex cations featuring a highly unusual linear and symmetric M–I–M moiety are each surrounded by one of these 14-member polyiodide rings in a belt-like fashion. The structures of [Pd(cis-(HO)₂[14]aneS₄)](I₃)₂ and [Pd([9]aneS₃)₂](I₃)₂ both feature tri-iodides as counter-anions. In [Pd(cis-(HO)₂[14]aneS₄)](I₃)₂, quite asymmetric I₃⁻ ions form sinusoidal infinite chains via head-to-tail I₃⁻⋯I₃⁻ interactions; these chains run along the (001) direction and are stacked along the (100) direction to form highly puckered anionic layers via I⋯I weak interactions that cross-link the chains. In [Pd([9]aneS₃)₂](I₃)₂, [Pd([9]aneS₃)₂]²⁺ cations are bridged on each side by pairs of symmetric I₃⁻ ions through long-range S⋯I contacts to form discrete infinite ribbons that run parallel to the a axis. By contrast, the structure of [Pd([9]aneS₃)₂](I₅)₂ consists of highly puckered polyanionic layers featuring fused 18-member polyiodide rings made up of I₅⁻ ions. Two of these layers related by an inversion center are stacked along the b axis and interact with each other to form large cavities within which the complex cations sit. In these complex arrays the cation can be regarded as a template around which polyanion networks can be structured. The solid state FT-Raman spectra of the reported polyiodides are discussed on the basis of their crystal structures.     

Benetzung und Zwickelflüssigkeit bei zwei nebeneinander liegenden Zylindern

The characteristic properties for the wetting of a solid by a liquid are the liquid-surface tension σ′, the contact angle ? and the solid-surface tension σ?. For these three properties an empirical equation is developed, which is also applicable to mercury. Many results of various measurements of the three characteristic properties are collected for 14 diffrent solid materials of packing elements and packings. For two above one another lying and two side by side lying particles as spheres or long cylinders the liquid contour was calculated by different authors. Thereby the contact angle was only varied between 0° and 90°. Here the model of Batel [36] for two side by side lying cylinders is extended. The advancing contact angle and the receding contact angle were used. The model was evaluated for contact angles between 5° and 175°. The results shows the importance of the wetting property 0, 5(1+cos ?).     

Uniaxial Pressure Control of Superconductivity via Stripe Instability in La1.64Eu0.2Sr0.16CuO4 Crystals

Uni-axial pressure dependence of the superconducting critical temperature (T _c) with a static stripe instability was examined in La_1.64Eu_0.2Sr_0.16CuO₄ single crystals. We find anisotropy in the dependence of T _c on uni-axial pressure applied along the tetragonal [001], [100], and [110] directions. The behavior of dT _c/dP _[001] and dT _c/dP _[100] is essentially the same as that in the dynamical stripe phase of Eu-free La_1.84Sr_0.16CuO₄. In contrast, novel behavior observed in dT _c/dP _[110] in the present material is attributed to the weakening of static stripe order. Our result points toward a promising new way to control the superconducting state with uni-axial pressures via a coupling of the stripe instability to the underlying lattice symmetry.     

Simple chemical solution deposition and thermoelectric properties of epitaxial La0.95Sr0.05CoO3 thin films

In this paper, simple chemical solution deposition method is used to prepare La_0.95Sr_0.05CoO₃ thin films on SrTiO₃ (001) substrates by acetate-based precursors. The derived film is characterized by x-ray diffraction, field-emission scanning electron microscopy and transmission electronic microscopy. The derived film is epitaxial growth with < 001>[100] La_0.95Sr_0.05CoO₃||<001>[100] SrTiO₃, indicating that the chemical solution deposition is an effective route to obtain the cobalt-based films. The resistivity, Seebeck coefficient and thermal power factor are 0.05Ω cm, 250 μV/K and 0.21 mWK^− 2m^− 1 at 300 K, respectively, which is higher than these of the ceramics, indicating epitaxial thin film is an effective route to enhance the thermoelectric properties of La_0.95Sr_0.05CoO₃.     

Performance of a scintillating glass calorimeter for electromagnetic showers

A scintillating glass electromagnetic calorimeter consisting of 3 × 3 moduls of 8 × 8 × 66 cm³ each has been studied with electrons in the energy interval 14.7 MeV < E < 6000 MeV. An energy resolution of σ_E/E[%] = √1.6²/E[GeV] + 1.0² was achie spatial resolution turns out to be of the order σ = 4 to 8 m depending on the impact point and the angle of incidence; it improves with increasing energy. The observations are in excellent agreement with the result of an EGS Monte Carlo simulation of the detector including optical effects and photoelectron statistics.     

Roles of lattice fitting in epitaxy

The epitaxial orientations of three series of materials-alkali halides, chalcogenide compounds and face-centered cubic metals-and of indium (face-centred tetragonal structure) and iron (body-centred cubic structure) on a (001) MgO substrate were examined by in situ electron microscopy and diffraction. The lattice parameter ratio ? = a_d/a_s (d, deposit;s, substrate) ranges from 0.95 for LiF to 1.68 for KI, from 1.41 for PbS to 1.53 for PbTe and from 0.84 for nickel to 1.18 for lead. A systematic dependence of the epitaxial orientation on ? is found: alkali halides and chalcogenide compounds with ? around 1 or 1.5 prefer the (001) parallel orientation with (001)_d(001)_s, [100]_d[100]_s, but those with a value of ? around √2 prefer the (001) orientation with (001)_d(001)_s, [110]_d[100]_s. Metals with ? near 1 also prefer the (001) parallel orientation, but copper and nickel with ? around 0.85 prefer the (1$\text{1}$0) orientation with (1$\text{1}$0)_d(001)_s, [11$\text{2}$]_d[100]_s, and gold, indium and lead with values of ? of 0.97, 1.17 (1.09) and 1.18, respectively, favour the (111) orientation with (111)_d(001)_s, [1$\text{1}$0]_d[1$\text{1}$0]_s. The epitaxial relation is discussed in terms of the fit of the lattice spacings of the deposit and substrate crystals.     

HRTEM and EELS Studies on Structural Defects in the Superconductor Sr2CuO2+δCl2−y Newly Synthesized Under High Pressure

Structural defects in the newly high-pressure synthesized superconductor Sr₂CuO_2+δCl_2−y have been studied by means of high-resolution transmission electron microscopy and parallel electron energy-loss spectroscopy. Two types of grain boundaries were found in the material. One is the amorphous boundaries usually lying in the ab-planes. The other is the structurally intact grain boundaries, and most of them are large-angle boundaries. One of the large angles frequently observed is the 90°〈110〉 asymmetrical tilt boundary. In some domains, periodicity lengths were changed due to the lattice distortion usually associated with atom deficiency. These domains can be regarded as “second-phase particles” embedded in the perfect grains. O-K electron energy-loss spectroscopy results suggest that those defect domains are in the hole-poor states. Quantitative composition analysis from energy dispersive of X-ray suggests the hole-poorness is caused by oxygen deficiency. Dislocations, such as the a[110] and c[001] edge dislocations, were also observed in the material. In most cases, those dislocations are very complex and exhibit stacking faults. PACS: 68.37.Lp, 67.80.Mg, 74.72.Jt     

Influence of Cu off-stoichiometry on wide band gap CIGSe solar cells

The electric properties of solar cells based on co-evaporated Cu(In,Ga)Se₂ (CIGSe) thin film show a good tolerance regarding the absorber Cu content (y = [Cu]/([In] + [Ga])) for standard Ga concentration, i.e. x = [Ga] / ([In] + [Ga]) ~ 0.3. In the present contribution, we show that this tolerance is lost when the gallium content is increased. Wide bandgap CIGSe samples (x ~ 0.55) with a variation in y from 0.97 to 0.84 have been grown. The efficiency of the cells decreases from 12.6% to 6.5% for y = 0.97 and 0.84 respectively. For the lowest y, the efficiency is harmed because of a low short-circuit current density (J_sc), an increased voltage dependency in the current collection, which affects the fill factor (FF), and a decrease of the open-circuit voltage (V_oc). For y = 0.97 and 0.84 respectively, the decrease of the activation energy (E_a) from 1.36 to 1.24 eV indicates a shift of the area of the dominant recombination from the space charge region towards the interface. There seems to be evidence that reducing the Cu-content in the CIGSe thin film will cause a decrease in the width of the space charge region. Solar cells based on Cu-rich CIGSe (1.03 < y < 1.09) have also been fabricated and characterized. A strong deterioration of their electrical properties is observed despite the KCN etch of the segregated Cu_2 − xSe binary phases at the surface, suggesting the presence of residual Cu_2 − xSe precipitates within the layer.     

Epitaxial EuO thin films by pulsed laser deposition monitored by in situ x-ray photoelectron spectroscopy

We have grown EuO thin films on silicon [001] and yttrium aluminate [110] from a europium metal target using pulsed laser deposition. In situ x-ray photoelectron spectroscopy has been used to determine the parameter window for stoichiometric EuO deposition. EuO is observed to grow in the relatively high pressure regime of 10⁻⁶-10⁻⁵ mbar, due to the large Eu flux during ablation. EuO is proven to grow epitaxially on yttrium aluminate [110]. Magnetization measurements confirm the stoichiometry of the film.     

The kinetics of surface craze growth in polycarbonate exposed to normal hydrocarbons

A variable radius of curvature strain bending apparatus has been used to investigate the propagation of surface crazes in polycarbonate exposed to a series of normal hydrocarbons fromn-hexane ton-dodecane. In all cases it was found that for crazes growing in a zone free of other crazes, the growth rate was linear at constant temperature, and exponentially dependent upon temperature. An activated-state theory was developed to describe the kinetics of growth in terms of two parameters,B, a dimensionless strain constant which was independent of both the test variables and the crazing agent used, andA′ a characteristic growth rate parameter that varied exponentially with temperature whereA′=G₀ exp —ΔE _G/RT. The rate constantG ₀ and the activation energy ΔE _G correlate with the square of the difference between the solubility parameters of the crazing agent and polycarbonate.