Measurement and theory of the orientation dependence of Knoop microhardness in single-crystal mercuric iodide

Measurements were made of the orientation dependence of the Knoop microhardness H _K on the (001) and (110) faces of single crystals of red (tetragonal) mercuric iodide that were vapour-grown for use in radiation detectors. The (001) faces of the crystals are softest when the major diagonal of the Knoop indentor (called here the indentor) is parallel to the [100] crystallographic axis, and H _K increases monotonically, by about 25%, as the indentor is rotated from the [100] to the [110] axis. The (110) surfaces are hardest when the indentor is parallel to [001]; H _K decreases by about 50% as the indentor is rotated from [001] to [1¯10]; the experimental data indicate an intermediate microhardness minimum that occurs before the [1¯10] orientation is reached. Particularly interesting surface topography, including bands of slip lines, is observed in the vicinity of indentations on the (110) planes, which apparently have not previously been characterized by Knoop microhardness indentation. Theoretically, the size of a microhardness indention is presumed to depend on the volume of material in which appropriate slip systems are stressed sufficiently to cause appreciable slip. To test this concept and determine which particular slip systems dominate the indention process, the infinite flat punch model was used to calculate the orientational and volumetric variations of shear stress on various potential slip systems in mercuric iodide. For indention processes controlled by movement (i.e. slip) of material in the [001] direction, over {100} planes, these calculations predict the following (experimentally observed) results: (a) on the (001) plane, H _K is smallest at [001] and greatest at [110], with no intermediate extremum; (b) on the (110) plane, H _K has its greatest value at [001] and a minimum between [001] and [1¯10]; (c) H _K at [110] on the (001) plane is essentially the same as H _K at [1¯10] on the (110) plane; and (d) the relative variation of H _K is greater on the (110) than on the (001) surface. Finally, the expected orientational variation of H _K on the (100) and (101) surfaces was determined theoretically.     

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.     

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.     

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.     

Microstructure of Y-PSZ after ageing at high temperature

Partially stabilized zirconia (PSZ) materials containing 2.5 and 5.0 mol % Y₂O₃ were prepared by pressureless sintering and aged at 1200° C for 1000 IS, and their microstructures were analysed by transmission electron microscopy and electron diffraction methods. Tetragonal zirconia polycrystal (TZP) containing 2.5 mol % Y₂O₃ before ageing showed nearly 100% tetragonal microstructure and 0.5 m grain size, but after ageing the microstructure changed greatly, exhibiting no simple grain structure over wide areas. Repeated twin structures within the grains were observed. Y-PSZ material containing 5.0M01% Y₂O₃ before ageing showed a tetragonal (I structure within a cubic (c) stabilized ZrO₂ matrix, After ageing, structures of fine strip crystals crossed each other orthogonally within the cubic matrix and typical diffuse scattering in the diffraction pattern was observed. Repeated twins were found on the plane of (100)_m, and the orientational relationship between tetragonal (t) and monoclinic (m) crystal was determined to be (100)_m [(100)_t, [010]_m \tT [001b]_t.     

Role of some rare earth (RE) ions (RE = La, Pr, Nd, Sm, Gd and Dy) in crystal and mechanical behaviours of sol-gel derived ZrO2-2 mol% REO2O3 spun fibres calcined at 1300°C

Crystal behaviours such as crystallization temperature (amorphous to tetragonal (t) zirconia), tendency of phase transformation (tetragonal to monoclinic (m) zirconia) and lattice strain were studied with mechanical property e.g. tensile strength of sol-gel derived ZrO₂-2 mol% RE₂O₃ (RE = La, Pr, Nd, Sm, Gd and Dy) spun fibres. Rare earth cations of varying sizes played a significant role in changing the above mentioned properties of ZrO₂-2 mol% RE₂O₃ fibres. It was found that with decreasing the ionic size difference between the zirconium and RE ions, crystallization temperature (amorphous →)t-ZrO₂) decreased, the probability of phase transformation (t→m) decreased, lattice strain which is related to lattice distortion decreased and tensile strength increased.     

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.     

Fermi surface deformation parameters and cyclotron effective masses in white tin

Oscillatory magnetostriction and the de Haas-van Alphen effect have been used to determine Fermi surface deformation parameters for cross sections lying normal to[001] in white tin. The temperature dependence of the amplitudes has been used to calculate effective masses for orbits lying normal to[001], [100], and[110].     

The structure of the unidirectionally solidified Al-Al2Au eutectic

The structure of a number of unidirectionally solidified Al-Al₂Au alloys of eutectic and off-eutectic compositions has been investigated over a wide range of growth rates (1.6×10^–4 to 1.66×10^–2cm sec^–1) using a thermal gradient of approximately 80 to 100 lamellar interface || (001)_{Al 2 Au} || (01 1) _Al [ 1 1 0 ]_{Al 2 Au} || [ 1 0 0 ] _Al growth direction of lamellae and rods || [ 1 1 0 ]_{Al2 Au} || [ 1 0 0 ]_Al \begin{gathered} lamellar interface \left\| {(001)_{Al_{ 2} Au} } \right.\left\| {(01 1)} \right._{Al} \hfill \\ \left[ {1 1 0} \right]_{Al_{ 2} Au} \left\| {\left[ {1 0 0} \right]} \right._{Al} \hfill \\ growth direction of \hfill \\ lamellae and rods \left\| {\left[ {1 1 0} \right]_{Al_2 Au} \left\| {\left[ {1 0 0} \right]_{Al} } \right.} \right. \hfill \\ \end{gathered}     

Coarsening of δ-Ni<Subscript>2</Subscript>Si precipitates in a Cu–Ni–Si alloy

The coarsening behavior of rod-shaped and spherical δ-Ni₂Si precipitates in a Cu–1.86 wt% Ni–0.45 wt% Si alloy during aging at 823–948 K has been investigated by measuring both precipitate size by transmission electron microscopy (TEM) and solute concentration in the Cu matrix by electrical resistivity. The rod-shaped δ precipitates have an elongated shape along 〈[`5] 5 8 \overline{5} 5 8 〉_m and a {110}_m habit-plane facet. The coarsening theory of a spherical precipitate in a ternary alloy developed by Kuehmann and Voorhees (KV) has been modified to a case of rod-shaped precipitates. The coarsening kinetics of average size of the rod-shaped and spherical δ precipitates with aging time t obey the t ^1/3 time law, as predicted by the modified KV theory. The kinetics of depletion of the supersaturation with t are coincident with the predicted t ^−1/3 time law. Application of the modified KV theory has enabled calculation of the energies of sphere, {110}_m and rod-end interfaces from the data on coarsening alone. The energy of the {110}_m interface having a high degree of coherency to the Cu matrix is estimated to be 0.4 J m⁻², the incoherent sphere-interface energy 0.6 J m⁻², and the rod-end interface energy 5.2 J m⁻².     

Tetramethylammonium Neptunium(IV) Isothiocyanate [N(CH3)4]4[Np(NCS)8]

A new Np(IV) complex, [N(CH₃)₄]₄[Np(NCS)₈], was prepared. Its crystal structure was determined, and the absorption spectra in the IR and near IR ranges were measured. Crystal data: a = 27.280(6), b = 12.288(3), c = 13.493(3) Å, space group Pna2₁, Z = 4, V = 4523(2) A³, R = 0.044, wR(F ²) = 0.091. The crystal structure of the compound consists of [Np(NCS)₈]^{4 -} anions and N(CH₃)₄ ⁺ cations. The coordination polyhedron of the Np atom is a distorted tetragonal antiprism formed by the nitrogen atoms of eight NCS^- ions.     

Energies of [001] small angle grain boundaries in aluminum

Energies of symmetric [001] tilt and twist small angle grain boundaries in aluminum have been examined as a function of misorientations. Boundary energies were evaluated relative to solid/liquid interfacial energies by a dihedral angle method on surface grooves. Energies of (100)_s tilt boundaries with the Burgers vector of a[100] were rather smaller than those of (110)_s tilt boundaries with a/2[110]. Energies of twist boundaries at θ < 4^∘ were slightly larger than those of (110)_s tilt boundaries. The energies were well explained as a function of misorientations by the Read-Shockley type equation. The equation also correctly described the difference in elastic energy factors between the (110)_s tilt and twist boundaries. However, the term b in the equation may take a constant value independent of the Burgers vectors.     

Asymptotic properties in partial linear models under dependence

Consider the regression modely _i =ζ _i ^T β+m(t _i )+ε _i fori=1,...,n. Here (ζ _i ^T ,t _i ) ^T ∈ℝ ^p ×[0,1] are design points, β is an unknownp×1 vector of parameters,m is an unknown smooth function from [0,1] to ℝ andε _i are the unobserved errors. We will assume that these errors are not independent. Under suitable assumptions, we obtain expansions for the bias and the variance of a Generalized Least Squares (GLS) type regression estimator, and for an estimator of the nonparametric functionm(·). Furthermore, we prove the asymptotic normality of the first estimator. The obtained results are a generalization of those contained in Speckman (1988), who studied a similar model with i.i.d. error variables. Research supported by the Xunta de Galicia (Spain) and the DGES (Spain) under research projects XUGA 10503A98 and PB98-0182-c02-01, respectively.     

A new yellow fluorescent dopant for high-efficiency organic light-emitting devices

We describe the design and synthesis of a sterically hindered yellow dopant, tetra(t-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq₃) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq₃ and 20 mA/cm² current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 lm/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIE_x,y) = [0.52, 0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices.     

Sublimation growth of titanium nitride crystals

The sublimation-recondensation growth of titanium nitride crystals with N/Ti ratio of 0.99 on tungsten substrates is reported. The growth rate dependence on temperature and pressure was determined, and the calculated activation energy was 775.8 ± 29.8 kJ/mol. The lateral and vertical growth rates changed with the time of growth and the fraction of the tungsten substrate surface covered. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45° angle between TiN [100] and W [100], occurs not only for TiN crystals deposited on (001) textured tungsten but also for TiN crystals deposited on randomly orientated tungsten. This study demonstrates that this preferred orientational relationship minimizes the lattice mismatch between the TiN and tungsten.     

Anisotropy of microhardness on the (001) plane of ionic crystals such as NaCl

The anisotropy of microhardness,H, was investigated for the series of KCl-NaCl-NaF-LiF-MgO crystals using a Vickers indentor. The anisotropy had a similar character for deformation temperatures of 77, 293 and 800 K (H _[100] >H _[110]; however, the main factors affecting it were different for low and high temperatures. The dependence of the anisotropy coefficientK = (H =_[100] –H _[110] on the crystal hardness was found and it was shown that this dependence was significantly influenced by the deformation temperature. The results obtained support the dislocation mechanism of indentation formation on the crystals investigated.     

Epitaxial growth of CoSi2 on Si(001) by reactive deposition epitaxy: Island growth and coalescence

Epitaxial CoSi₂ layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi₂(001) follows the Volmer-Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t_Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi₂/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)_CoSi2||(001)_Si and [100]_CoSi2||[100]_Si. Platelet-shaped CoSi₂ islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)_CoSi2||{111}_Si) and their narrow 〈110〉 directions by {511}_CoSi2||{111}_Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}_CoSi2||(001)_Si, and {1¯1¯1}, with {1¯1¯1}_CoSi2||{11¯1}_Si, respectively. The early stages of film growth (t_Co ≤ 13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2 × 1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t_Co ≥ 13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi₂(001) layer, with a twin density of 2.8 × 10¹⁰ cm^− 2, is obtained at t_Co = 50 Å.     

Synthesis and Crystal Structure of Cs4[UO2(CO3)3]

Light green transparent crystals of Cs₄[UO₂(CO₃)₃] were prepared by evaporation from aqueous solutions. The crystal structure was refined to R ₁ = 0.039 (wR ₂ = 0.081) for 2311 reflections with |Fhkl| 4|Fhkl|. Monoclinic system, space group C2/c, a = 11.5131(9), b = 9.6037(8), c = 12.9177(10) Å, = 93.767(2)°, V = 1425.2(2) ų. The structure of Cs4[UO2(CO3)3] consists of isolated complex ions [UO₂(CO₃)₃]^{4 -} formed by uranyl cation UO₂ ^{2 +} and three CO₃ ^{2 -} groups. The equatorial planes of the [UO₂(CO₃)₃]^{4 -} ions are approximately parallel to the (201) plane. The nine-coordinate Cs⁺ cations are located between the complex anions. The compound is isostructural with M4[UO2(CO3)3] with M = K, NH₄, and Tl, but not isostructural with Na₄[UO₂(CO₃)₃].     

Differential equations determining the function that describes precatastrophic behavior of a system

Based on an analysis of the experimental data obtained for various catastrophic phenomena, Malinetskii et al. [1] considered the main parameters of a process preceding the catastrophe and proposed the following function of time that describes this process: I(t) = A + B(t _c ? t)^α[1 + Ccos(θ log(t _c ? t) ? ?)]. The passage to complex quantities and substitution of variables reveal a power-law character of this approximation. Using this approach, differential equations determining the function that describes the precatastrophic behavior are obtained.     

Epitaxial growth and electrical measurement of single crystalline Pb(Zr0.52Ti0.48)O3 thin film on Si(001) for micro-electromechanical systems

We report in this work the epitaxial growth and the electrical characteristics of single crystalline Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film on SrTiO₃(STO)-buffered Si(001) substrate. The STO buffer layer deposited by molecular beam epitaxy allows a coherent oxide/Si interface leading enhanced PZT crystalline quality. 70 nm-thick PZT (52:48) layer was then grown on STO/Si(001) by sol-gel method. X-ray diffraction demonstrates the single crystalline PZT film on Si substrate in the following epitaxial relationship: [110] PZT (001)//[110] STO (001)//[100] Si (001). The macroscopic electrical measurements show a hysteresis loop with memory window of 2.5 V at ± 7 V sweeping range and current density less than 1 μA/cm² at 750 kV/cm. The artificial domains created by piezoresponse force microscopy with high contrast and non-volatile properties provide further evidence for the excellent piezoelectric properties of the single crystalline PZT thin film.