Orientation dependence of electrical properties of 0.96Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-0.04BaTiO<Subscript>3</Subscript> lead-free piezoelectric single crystal

In this paper, a single crystal of 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T _m, ε _m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718), (305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were obtained by investigating the piezoelectric constants d ₃₃ as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d ₃₃ values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied during the poling process. The as-grown 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10⁻¹¹ Ω⁻¹⋅m⁻¹ and 3.95×10⁻⁹ Ω⁻¹⋅m⁻¹ at 25°C and 150°C for the 〈001〉 oriented crystal sample.     

Metallic beta-phase silicon nanowires: Structure and electronic properties

Electronic band structure and energetic stability of two types of 〈110〉 and 〈001〉 oriented silicon nanowires in β-Sn phase with the surface terminated by hydrogen atoms were studied using density functional theory. It was found that β-Sn nanowires are metastable with zero band gap against to nanowires in diamond phase. The relative energy of the studied wires tends to the energy of the bulk silicon crystal in β-Sn phase.     

Quark Confinement Mechanism and the Scale Λ QCD

The confinement mechanism proposed earlier by the author is applied to problem of arising the so-called scale Λ _QCD within the framework of QCD. The natural physical assumption consists of that 1/Λ _QCD  ∼ 〈r〉 where 〈r〉 is a characteristic size of hadron (radius of confinement). The above confinement mechanism allows us to calculate 〈r〉 for mesons in terms of quark and gluonic degrees of freedom and this permits to conclude that Λ _QCD should slightly change from hadron to hadron.     

Kinetic-growth self-avoiding walks on small-world networks

Kinetically-grown self-avoiding walks have been studied on Watts-Strogatz small-world networks, rewired from a two-dimensional square lattice. The maximum length L of this kind of walks is limited in regular lattices by an attrition effect, which gives finite values for its mean value 〈L 〉. For random networks, this mean attrition length 〈L 〉 scales as a power of the network size, and diverges in the thermodynamic limit (system size N ↦∞). For small-world networks, we find a behavior that interpolates between those corresponding to regular lattices and randon networks, for rewiring probability p ranging from 0 to 1. For p < 1, the mean self-intersection and attrition length of kinetically-grown walks are finite. For p = 1, 〈L 〉 grows with system size as N^1/2, diverging in the thermodynamic limit. In this limit and close to p = 1, the mean attrition length diverges as (1-p)^-4. Results of approximate probabilistic calculations agree well with those derived from numerical simulations.     

Superparamagnetism in the 1D Ising model

The temperature dependence of the order parameter (〈M ²〉, the mean-square spin excess per spin) for a system with a finite number of spins of the 1D Ising model was investigated. It was shown that there is a nonzero temperature T _s below which 〈M ²〉 rapidly tends to unity. The analogy between the 1D ensemble of a finite number of spins and a system of superparamagnetic particles is discussed.     

X-ray dosimetric characteristics of CdIn2S4〈Cu〉 single crystals

The effect of doping CdIn₂S₄ single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic X-ray conductivity of CdIn₂S₄〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn₂S₄ at effective radiation hardness V _a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage of a CdIn₂S₄〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn₂S₄〈Cu〉 on the X-ray dose is described as ΔI _{E, 0} ∝ E ^α, where 0.6 ≤ α ≤ 1.8.     

Nuclear charge radii from optical spectroscopy

The changes of the mean-square nuclear charge radii have been re-evaluated [3] on an equivalent basis, using all available data from optical spectroscopy. The steps of evaluation are discussed and the results are presented in a number of diagrams, showing the course of 〈r ²〉 fromN=20 toN=152 and showing details of δ〈r ²〉     

Swelling of two-dimensional polymer rings by trapped particles

The mean area of a two-dimensional Gaussian ring of N monomers is known to diverge when the ring is subject to a critical pressure differential, p _c ∼ N ^-1. In a recent publication (Eur. Phys. J. E 19, 461 (2006)) we have shown that for an inextensible freely jointed ring this divergence turns into a second-order transition from a crumpled state, where the mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N ². In the current work we extend these two models to the case where the swelling of the ring is caused by trapped ideal-gas particles. The Gaussian model is solved exactly, and the freely jointed one is treated using a Flory argument, mean-field theory, and Monte Carlo simulations. For a fixed number Q of trapped particles the criticality disappears in both models through an unusual mechanism, arising from the absence of an area constraint. In the Gaussian case the ring swells to such a mean area, 〈A〉 ∼ NQ, that the pressure exerted by the particles is at p _c for any Q. In the freely jointed model the mean area is such that the particle pressure is always higher than p _c, and 〈A〉 consequently follows a single scaling law, 〈A〉 ∼ N ² f (Q/N), for any Q. By contrast, when the particles are in contact with a reservoir of fixed chemical potential, the criticality is retained. Thus, the two ensembles are manifestly inequivalent in these systems. An erratum to this article is available at .     

Thermal oxidation effect on structural and optical properties of?heavily doped phosphorus polycrystalline silicon films

The study reported in this paper contributes to better understanding the thermal oxidation effect on structural and optical properties of polycrystalline silicon heavily in situ P-LPCVD films. The deposits, doped at levels 3×10¹⁹ and 1.6×10²⁰ cm⁻³, have been elaborated from silane decomposition (400 mTorrs, 605°C) on monosilicon substrate oriented 〈111〉. The thermal oxidation was performed at temperatures: 850°C during 1 hour, 1000, 1050, and 1100°C during 15 minutes. The XRD spectra analysis pointed out significant 〈111〉 texture evolution, while in the case of 〈220〉 and 〈311〉 textures, the intensities are practically invariant (variations fall in the uncertainty intervals). The optical characterizations showed that refractive index and absorption coefficient are very sensitive to the oxidation treatment, mainly when the doping level is not very high. We think that atomic oxygen acts as defects passivating agent leading to carriers’ concentration increasing. Besides, the optical behavior is modeled in visible and near infrared, by a seven-term polynomial function n ²=f(λ ²), with alternate signs, instead of theoretically unlimited terms number from Drude’s model. It has been shown that fitting parameters fall on Gaussian curves like they do in the theoretical model.     

Morphologies of solid-liquid interface and surface steps during rapid growth of BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> single crystals

The evolution of solid-liquid interface during BBO single crystal growth was studied by the differential interference microscopy. And the step morphology on (0001) surface of the as-grown crystal was observed by the atomic force microscopy as well. It was found that the transition from a flat solid-liquid interface to a skeletal shape will occur in case of rapid growth. However, AFM images of surface steps revealed morphology differences correlated with crystallographic directions. The steps advancing along 〈10 0〉 direction form the step flow, whereas those steps propagating along 〈01 0〉 direction shape into step segments. Measurements of step heights by AFM indicated that it is the high anisotropy of the dimension of growth unit and step bunching due to the enlargement of concentration difference along the surface that results in the anisotropy of step morphologies. Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623)     

Anisotropy of the upper critical field and specific heat in V3Si — a superconductor with cubic symmetry

The specific heat of a V₃Si single crystal (T _c=17 K, H _c2=20 T) in magnetic fields up to 8 T isinvestigated experimentally for three orientations of the field relative to the crystallographic directions — H∥〈001〉, H∥〈110〉, and H∥〈111〉. Both the upper critical magnetic field and the specific heat of the mixed state are observed to depend on the orientation of the magnetic field relative to the crystallographic directions (anisotropy): The critical field reaches its maximum value and the specific heat its minimum value in a field along the 〈001〉 direction. The anisotropy scale in both phenomena increases as the magnetic field and reaches 3% in a 6 T field. The interrelationship of the upper critical field anisotropy and the specific-heat anisotropy in type-II superconductors is studied. It is shown that the anisotropy of the specific heat in the mixed state in weak fields can serve as a criterion for nontrivial pairing. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 26–29 (10 January 1999)     

The bordoni peak in silver single crystals at megahertz frequencies

Summary The dislocation relaxation maximum has been investigated at frequencies of 5, 10 and 30 MHz. The three (very high-purity) silver crystals of crystallographic orientation 〈111〉, 〈110〉 and 〈100〉 which are given a resolved shear stress of 20 MPa were found to produce dislocation relaxation maximum at 107 K in all the three samples. The maximum shifts to 117 K when measurement is carried out at 10 MHz and to 127 K at 30 MHz. The results reveal that the maximum is orientation independent. The activation energy and the attempt frequency were calculated and found to be equal to 0.105 eV and 2·10⁹ Hz, respectively. Meanwhile the larger magnitude of the maximum was found on the 〈111〉 crystal and the least was on the 〈100〉 crystal. Finally, it was clearly shown that the dislocation relaxation strength decreases as the frequency increases.     

Intervalley scattering in GaAs: ab initio calculation of the effective parameters for Monte Carlo simulations

Interactions between excited electrons and short-wavelength (intervalley) phonons in GaAs are studied using density functional theory for the conduction bands, and density functional perturbation theory for phonon frequencies and matrix elements of the electron–phonon interaction. We have calculated the deformation potentials (DPs) and the average intervalley scattering time 〈τ〉. The integration of the scattering probabilities over all possible final states in the Brillouin zone has been performed without any ad hoc assumption about the behavior of the electron–phonon matrix elements nor the topology of the conduction band. For transitions from the L point to Γ valley (within the first conduction band), we find 〈τ〉_L to be 1.5 ps at 300 K, in good agreement with time-resolved photoluminescence experiment. We discuss the difference between our calculated DPs, and effective parameters used in Monte Carlo simulations of optical and transport properties of semiconductors. The latter are based on Conwell’s model, in which electron–phonon interaction is described by one single constant and a parabolic model is used for conduction bands. We deduce the effective DP from our 〈τ〉, and compare it to our calculated DPs. We conclude that only effective DPs obtained from a full calculation of 〈τ〉 are relevant parameters for Monte Carlo simulations. PACS 71.10-w; 72.10.Di; 71.55.Eq     

Dependence of the frequencies of magnetostatic waves on the magnetizing field in ferrite films

Analytical expressions are derived for the derivatives of the frequencies of magnetostatic waves with respect to the external magnetic field in anisotropic ferromagnetic films. Films having cubic anisotropy and 〈100〉, 〈110〉, and 〈111〉 surfaces are analyzed in detail. The frequency-field relations are used in an experimental determination of the temperature coefficients of the cubic anisotropy field and the saturation magnetization in an yttrium iron garnet film. Fiz. Tverd. Tela (St. Petersburg) 40, 2089–2092 (November 1998)     

Change of superdislocation splitting with strain in single crystals of the Ni3Fe ordered alloy

The method of transmission electron microscopy is used to study the dislocation structure in single crystals of the Ni ₃ Fe ordered alloy for different degrees of strain. The [1812], [011], [111] and [001] single crystal orientations are examined. The superdislocation splitting (r) is measured for different degrees of strain, distributions of r are constructed, and their average values 〈r〉 are estimated. The 〈r〉-ε curves are constructed. With the use of the experimental r values, the effective energy of antiphase boundaries ζ* is estimated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 51–56, January, 2006.     

Smoothening transition of a two-dimensional pressurized polymer ring

We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure, p_c ∼ N^-1, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N². The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is found, in which 〈A〉 ∼ N^3/2. For p ≫ p_c we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state.     

Statistical mechanics of braided Markov chains: I. Analytic methods and numerical simulations

We investigate numerically and analytically the statistics of Markov chains on so-called braid (B _n ) and locally free (ℒℱ _n ) groups. Namely, we compute the mean length 〈μ〉 and the variance 〈μ²〉−〈μ〉² of the shortest word which remains after applying of all group relations to the randomly generatedN-letter word (Markov chain). We express the conjecture (numerically justified) that the mean value 〈μ〉 for the random walk on the groupB _n (n≫1) coincides with high accuracy with the same value for the random walk on the “locally free group weth errors” if the number of errors is of order of 20%.     

A model to study the scaling of traffic fluctuations on complex networks

In a recent article, we studied the dynamics of traffic in complex networks [CITE]. In particular, we computed how the fluctuations scale with the mean, σ∼〈f 〉^α. Using a general model which includes nodes with finite capacity we found a continuous range of α values between 1/2 and 1. Here we resume the results, adding a brief analysis about the self-similarity of the traffic dynamics in our model.     

Using the full Raman depolarisation in the determination of the order parameters in liquid crystal systems

The depolarisation ratio for the Raman-active phenyl stretching mode has been measured over the whole of the mesophase range, and the orientational order parameters deduced, in the uniaxial nematic liquid crystal octylcyanobiphenyl (8CB). Linearly polarised light was incident normally on a homogeneously aligned sample and a χ² minimisation routine performed on the 360^° depolarisation ratio profile. The order parameters 〈P ₂₀₀〉 and 〈P ₄₀₀〉 , together with the differential polarisability ratio, r , are used as fitting parameters and measured as a function of temperature. Interestingly, we show that the value for r , conventionally measured in the isotropic phase and assumed to remain constant, has a clear temperature dependence, ranging from -0.032±0.008 in the isotropic phase through to -0.245±0.015 at the nematic-to-smectic A phase transition. The measured order parameters 〈P ₂₀₀〉 and 〈P ₄₀₀〉 varied from 0.35- 0.55±0.02 and 0.180- 0.245±0.02 , respectively, across the 8 ^° C wide nematic phase range. The values of both 〈P ₂₀₀〉 and 〈P ₄₀₀〉 are in excellent agreement with theory, but it is noteworthy that 〈P ₄₀₀〉 shows a much better quantitative match than has been reported in previous work. Crucially the temperature dependence of r is shown to be a contributing factor in the low 〈P ₄₀₀〉 values that have been conventionally reported from Raman scattering measurements. The potential for fitting the entire angular depolarisation ratio distribution in liquid crystalline systems that are described by more order parameters, specifically biaxial materials, is discussed.     

Temperature scaling of ferroelectric hysteresis in hard lead zirconate titanate bulk ceramic

The temperature scaling of the ferroelectric hysteresis was investigated in hard lead zirconate titanate (PZT) bulk ceramic. The power-law temperature scaling relations were obtained for hystersis area 〈A〉, remnant polarization P_r, and coercivity E_C in the forms of 〈A〉∝T^-0.9650, P_r∝T^-0.0261, and E_C∝T^-0.8823, respectively, which are mostly comparable to those of its soft counterpart. The observation that P_r decayed more slowly with temperature than in soft PZT was attributed to the presence of the complex defects in hard PZT. However, the product of P_r and E_C still provided the similar scaling law on the T dependence in comparison with 〈A〉. PACS 77.80.-e; 77.80.Fm; 77.84.-s; 77.84.Dy