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.     

Dielectric and orientational properties of nematogenic 4-<Emphasis Type="Italic">n</Emphasis>-octyl(4′-cyanophenyl)benzoate

Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate (8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition, the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time in the nematic and isotropic phases, the orientational order parameter 〈P₂〉 has been determined. The values of 〈P₂〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption of the dichroic dye, dissolved as guest probe in the mesogenic host.     

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.     

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.     

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.     

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)     

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%.     

Acoustic wave propagation in barium monochalcogenides in the B1 phase

Temperature dependence of ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss have been studied in (NaCl-type) barium monochalcogenides [BaX, X = S, Se, Te], in the temperature range 50–500 K; for longitudinal and shear modes of propagation along 〈100〉, 〈110〉, 〈111〉 directions. Second and third order elastic constants have been evaluated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Gruneisen parameters, nonlinearity constants, nonlinearity constants ratios and viscous drag due to screw and edge dislocations have also been evaluated for longitudinal and shear waves at 300 K. In the present investigation, it has been found that phonon-phonon interaction is the dominant cause for ultrasonic attenuation. The possible implications of results have been discussed. The text was submitted by the authors in English.     

Evidence of an intermediate phase in ternary Ge<Subscript>7</Subscript>Se<Subscript>93-x</Subscript>Sb<Subscript>x</Subscript> glasses

The compositional dependence of thermal properties, such as glass transition temperature (T_g), non-reversing enthalpy change (ΔH_NR) and the specific heat capacity change (ΔC_p) of melt quenched Ge₇Se_93-xSb_x (21 ≤ x ≤ 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to modulated differential scanning calorimetry (MDSC). The glass transition temperature, T_g, which is a measure of global connectivity of the glass, has been found to increase with the addition of Sb. In addition, a change in slope has been observed in the composition dependence of T_g at an average coordination 〈r〉 = 2.40. The experimentally observed compositional variation of glass transition temperature, has been compared with the theoretical predictions from the stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is seen in the compositional variation of the relaxation enthalpy (ΔH_NR), which is centered around 〈r〉 = 2.40. The change in specific heat capacity (ΔC_p) at T_g is also found to exhibit a distinct minima at 〈r〉 = 2.40, suggesting that the structural rearrangements for the liquid in the glass transition region are minimized around 〈r〉 = 2.4.     

Lattice mechanical properties of noble and transition metals

A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C ₁₁,C ₁₂ andC ₄₄), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C ₁₂–C ₄₄), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y ₁), limiting value in the [110] direction (Y ₂), degree of elastic anisotropy (A), maximum frequencyω _max, mean frequency 〈ω〉, 〈ω ²〉^1/2=(〈ω〉/〈ω ⁻¹〉)^1/2, fundamental frequency 〈ω ²〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model potential for predicting a large number of physical properties of transition metals.     

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.     

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.     

Coumarin-Pyrazole Hybrid with Red Shifted ESIPT Emission and AIE Characteristics - a Comprehensive Study

The newly synthesized three coumarin pyrazole hybrid excited state intramolecular proton transfer (ESIPT) dyes show efficient charge transfer from the pyrazole ring and the coumarin towards the electron withdrawing dicyanovinylene group as revealed from the frontier molecular orbitals. Aggregation induced emission enhancement (AIEE) studies with 2-((3-(4-hydroxy-2-oxo-2H-chromen-3-yl)-1-phenyl-1H-pyrazol-4-yl)methylene) malononitrile showed 9 fold increase in the emission enhancement in 90% DMF-H₂O mixture. Lippert-Mataga theory explained the solvatochromic behavior of the dyes in various solvents. The charge transfer characteristics and non-linear optical (NLO) properties have been supported and correlated with bond length alternation, bond order alternation and vibrational spectrum. As values of bond order alternation (BOA) tend to be more towards negative and as the value of α increases β decreases while the values of γ depends on the values of α and β. The observed values of γ are positive which revealed that β contributes significantly. The dyes exhibit linear and NLO properties superior to urea. (E)-2-(3-(2-(3-(4-Hydroxy-2-oxo-2H-chromen-3-yl)-1-phenyl-1H-pyrazol-4-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile shows enhanced linear and non-linear properties among the three dyes.     

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     

Wave mechanics of two hard core quantum particles in A 1-D box

The wave mechanics of two impenetrable hard core particles in a 1-D box is analyzed. Each particle in the box behaves like an independent entity represented by a macro-orbital (a kind of pair waveform). While the expectation value of their interaction, 〈 V _HC (x) 〉, vanishes for every state of two particles, the expectation value of their relative separation, 〈 x 〉, satisfies 〈 x 〉≥λ/2 (or q ≥ π/d, with 2d=L being the size of the box). The particles in their ground state define a close-packed arrangement of their wave packets (with 〈 x 〉= λ/2, phase position separation Δϕ = 2π and momentum |q _o| = π/d) and experience a mutual repulsive force (zero point repulsion) f _o =h ²/2md ³ which also tries to expand the box. While the relative dynamics of two particles in their excited states represents usual collisional motion, the same in their ground state becomes collisionless. These results have great significance in determining a correct microscopic understanding of widely different many-body systems.     

Double-beta decay: Present status

The present status of double-beta-decay experiments (including the search for 2β ⁺, ECβ ⁺, and ECEC processes) are reviewed. The results of the most sensitive experiments are discussed. Average and recommended half-life values for two-neutrino double-beta decay are presented. Conservative upper limits on effective Majorana neutrino mass and the coupling constant of the Majoron to the neutrino are established as 〈m _ν 〉 < 0.75 eV and 〈g _ee 〉 < 1.9 × 10⁻⁴, respectively. Proposals for future double-betadecay experiments with a sensitivity for the 〈m _ν 〉 at the level of 0.01–0.1 eV are considered.     

Intermolecular energy transfer in mixed laser dyes: photophysical properties of triplet states

Triplet-singlet energy transfer in laser dyes have been studied in EPA at 77K using N₂ laser as an excitation source. Phosphorescence of the donor (D) and the delayed fluorescence of the acceptor (A) and their lifetimes have been measured for coumarin 102 (D)-rhodamine B(A) and 9(10H)-acridone (D)-rhodamine 6G(A) dye systems as a function of acceptor concentration. These data yield energy transfer rate constants of ∼10³ dm³ mol⁻¹ s⁻¹ for the donor acceptor combinations, consistent with the Forster mechanism. The phosphorescence quantum efficiency and other spectral parameters are also reported.     

Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript>-Si〈Mn〉-Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript> and Mn<Subscript>4</Subscript>Si<Subscript>7</Subscript>-Si〈Mn〉-<Emphasis Type="Italic">M</Emphasis> photodiodes

The current-voltage characteristics of Mn₄Si₇-Si〈Mn〉-Mn₄Si₇ and Mn₄Si₇-Si〈Mn〉-M photodiodes are studied experimentally. The current passage mechanism under illumination with hν ≥ E _g is considered. The role of a contact to Mn₄Si₇ in the provision of high photosensitivity under illumination of the base by light with hν ≥ 1.14 eV at low temperatures, 77–220 K, is analyzed. From electrical measurements, electron microscopic data for the Mn₄Si₇-Si〈Mn〉 interface, and photocurrent-voltage characteristics, a band diagram under the conditions of photocurrent passage is constructed. The high low-temperature photosensitivity of the diodes (I _ph/I _d ≥ 10⁹) is explained by the impact-ionization-induced modulation of the base conductivity and injection amplification of holes in the transition layer.     

Λ and K s 0 production in pC collisions at 10 GeV/c

The experimental data from the 2-m propane bubble chamber have been analyzed for pC → Λ(K _s ⁰ )X reactions at 10 GeV/c. The estimation of experimental inclusive cross sections for Λ and K _s ⁰ production in the p ¹²C collision is equal to σ_Λ = (13.3 ± 1.7) mb and σ _{K s} ⁰ = (4.6 ± 0.6) mb, respectively. The measured 〈Λ〉/〈π⁺〉 ratio from pC reaction is equal to (5.3 ± 0.8) × 10⁻², and it is approximately two times larger than the 〈Λ〉/〈π⁺〉 ratio simulated by the FRITIOF model and than that of experimental pp reactions at the same energy. The text was submitted by the authors in English.     

Mean square number fluctuation for a fermion source and its dependence on neutrino mass for the universal cosmic neutrino background

Using the general formulation for obtaining chemical potentialμ of an ideal Fermi gas of particles at temperature T, with particle rest mass m₀ and average density 〈N〉/V, the dependence of the mean square number fluctuation 〈ΔN ²〉/V on the particle mass m₀ has been calculated explicitly. The numerical calculations are exact in all cases whether rest mass energym ₀c² is very large (non-relativistic case), very small (ultra-relativistic case) or of the same order as the thermal energy k_BT. Application of our results to the detection of the universal very low energy cosmic neutrino background (CNB), from any of the three species of neutrinos, shows that it is possible to estimate the neutrino mass of these species if from approximate experimental measurements of their momentum distribution one can extract, someday, not only the density 〈N _v〉/V but also the mean square fluctuation 〈Δ _v ² 〉/V. If at the present epoch, the universe is expanding much faster than thermalization rate for CNB, it is shown that our analysis leads to a scaled neutrino massm _v instead of the actual massm _0v .