Photoluminescence in “hard” and “soft” ferroelectric ceramics

In the previous years the ferroelectrics perovskites has shown an increase in the study for optical applications. What do materials take advantage of, the so-called soft or hard dopants? In this work we try to clarify some of these aspects analyzing a classic perovskite-type structure system like Pb _0.95 Sr _0.05(Zr _0.53 Ti _0.47)_1?y Cr _y O _3?y/2 (PSZTC) andPb _1?3x/2 La _x (Zr _0.53 Ti _0.47)_1?y Nb _y O _3?y/2 (PLZTN), hard and soft respectively. Photoluminescence, optical absorption spectroscopy, Raman spectroscopy, structural and micro-structural measurements have been carried out. The results revealed the role of the Cr, La and Nb ion substitutions in photoluminescence spectra, energy gap, Raman response, morphology grain size and the symmetry presented in these materials near the morphotropic phase boundary (MPB).     

Relationship of structure and morphology to properties of “hard” elastic fibers and films

About 10 years ago it was discovered that highly crystalline polymers such as polypropylene and polyoxymethylene could be extruded in such a manner a s to produce remarkably elastic fibers and films which appeared superficially to behave like rubber or Spandex-type elastomers. Aside from the patent literature [l] these materials remained largely undescribed and unnoticed until the last 2 or 3 years when Clark and co-workers at duPont, and Quynn and co-workers at Celanese have published the first technical data and discussions [2-5].     

A study of measuring acoustic velocities of thin and hard sea-bed layers

It has been known that the error of measuring acousticveloicities of thin sediment layers by the well-known T~2-X~2 approach isusually untolerable,and that this approach is unavailable in the casewhere sea-bed is hard because no echo from any subsurface belowsea-bottom can be received.Therefore applying the ray-parametermethod to thin layers and the refraction.method to hard layers need tobe considered in an acoustic velocity measurement system composed of asound source and a towed hydrophone streamer.Some problems of practi-cal importance about the applications of the two methods,such asecho-data processing procedures and error estimations in measuring acous-tic veloicities,are discussed,and the effectiveness of theoretical analyseshas been verified through computer simulations.     

BaTiO3–ferrite composites with magnetocapacitance and hard/soft magnetic properties

BaTiO₃–ferrite multiphase composites were prepared starting from di-phase mixtures of α-Fe₂O₃ and BaTiO₃ powders. During the sintering step, the formation of small amounts of secondary phases with multifunctional character as BaFe₁₂O₁₉ or Ba₁₂Ti₂₈Fe₁₅O₈₄ was promoted. The resulting multiphase ceramic compounds show interesting dielectric, magnetic and small magnetocapacitance effect at low temperature. The coexistence of different magnetic phases with contrasting coercivities (hard/soft) was detected by the presence of ‘wasp-waisted’ M(H) hysteresis loops and first-order reversal curve analysis. The present approach demonstrates that active materials can be realised by controlling in situ reactions at the interfaces in ferroelectric–magnetic oxide composites.     

Mixing and its rate in ‘soft’ and ‘hard’ billiards motivated by the Lorentz process

Billiards corresponding to planar periodic Lorentz processes are considered in the usual (hard) sense and in the case when the hard core potential of the scatterers is replaced by some other circularly symmetric potential. A review on certain important aspects of the history of the subject is given and some new results on exponential decay of correlations are formulated. Both the results from the literature and those of our own mentioned are mathematically rigorous, nevertheless, proofs are only briefly sketched. For further details, see the preprint [Correlation decay in certain soft billiards, Commun. Math. Phys., in press].     

Capillary freezing or complete wetting of hard spheres in a planar hard slit?

Extensive simulations of a hard sphere fluid confined between two planar hard walls show the onset of crystalline layers at the walls at about 98.3% of bulk crystallization density rho(f) independent of the wall separations L(z), and is, hence, a single wall phenomenon. As the bulk density far from the wall rho(b) increases, the thickness of the crystalline film appears to increase logarithmically, with (rho(f)-rho(b)) indicating complete wetting by the hard sphere crystal of the wall-fluid interface. Increasing rho(b) further, we observe a jump in the adsorption which depends on L(z) and corresponds to capillary freezing. The formation of crystalline layers below bulk crystallization, the logarithmic growth of the crystalline film, its independence of L(z), and its clear distinction from capillary freezing lend strong evidence for complete wetting by the hard sphere crystal at the wall-fluid interface.     

Computation of disordered system from the first principles of classical mechanics and ℕℙ hard problem

We study the classical 1D Heisenberg spin glasses in the framework of nearest-neighboring model. Based on the Hamilton equations we obtained the system of recurrence equations which allows to perform node-by-node calculations of a spin-chain. It is shown that calculations from the first principles of classical mechanics lead to ?? hard problem, that however in the limit of the statistical equilibrium can be calculated by ? algorithm. For the partition function of the ensemble a new representation is offered in the form of one-dimensional integral of spin-chains’ energy distribution.     

Study on‘soft＇ and ‘hard＇ interactions in ^-pp （pp） collisions using HIJING and PYTHIA

This paper presents a study on ＇hard＇ and ＇soft＇ interactions in ^-pp （pp） collisions using a phenomenological model of HIJING, the jet-cone reconstruction method is employed to select the ＇hard＇ and ＇soft＇ event sub-samples from minimum bias events. It is found that the HIJING model can reproduce the energy scaling behaviour of mean transverse momentum （〈PT〉） distributions of charged hadrons versus multiplicity （Nch） in ＇soft＇ events. From the PYTHIA simulation comparing with the HIJING model, the enhancement of the kaon and proton yields from ＇hard＇ interactions comparing with ＇soft＇ interactions is observed to be due to the mini-jets effect. These mechanisms responsible for the increase of charged hadron＇s （PT） are different in ＇soft＇ and ＇hard＇ interactions.     

Asymptotic forms for hard and soft edge general β conditional gap probabilities

An infinite log-gas formalism, due to Dyson, and independently Fogler and Shklovskii, is applied to the computation of conditioned gap probabilities at the hard and soft edges of random matrix β-ensembles. The conditioning is that there are n   eigenvalues in the gap, with n?|t|$n?|t|$, t   denoting the end point of the gap. It is found that the entropy term in the formalism must be replaced by a term involving the potential drop to obtain results consist with known asymptotic expansions in the case n=0$n=0$. With this modification made for general n  , the derived expansions — which are for the logarithm of the gap probabilities — are conjectured to be correct up to and including terms O(log|t|)$\mathrm{O}(\log |t|)$. They are shown to satisfy various consistency conditions, including an asymptotic duality formula relating β   to 4/β$4/\beta$.     

Electrostrictive properties of thermoplastic polyurethane elastomer: Effects of urethane type and soft–hard segment composition

The electromechanical behavior of thermoplastic elastomer polyurethane (TPE-PU) is investigated under the effects of urethane type (ester and ether-types) and soft–hard segments at various electric field strengths and temperatures. The highest dielectric constant, electrical breakdown strength, and specific conductivity belong to the ester-type polyurethane (LPR matrix), while the lowest values are obtained from the ether-type polyurethane composing predominantly with the soft-segment (E 80A matrix). Under the electric field strength in the range between 0 and 2 kV/mm, the LPR matrix attains the storage modulus sensitivity (ΔG′/G′₀) up to 2 at 2 kV/mm. For the temporal response, the polyurethanes behave with good reproductively (number of cycles >10⁵ times) and with very good recoverability. The steady state behavior can be attained at the first actuation and at the electric field strength of 1 kV/mm. Furthermore, the storage modulus (G′) shows linearly negative responses with increasing temperature. In the deflection experiments, the deflection distance and the dielectrophoresis force increase monotonically with increasing electric field strength. All of the TPE-PU possesses very fast response times for activation (<10 s.) and deactivation (<5 s.). TPE-PU material is systematically shown here to be a potentially good actuator material with high efficiency based on the electrostrictive performance data obtained.     

Design and fabrication of broad angular range depth-graded C/W multilayer mirror for hard X-ray optics

Recently, with the development of hard X-ray telescopes[1-3] and the third generation synchrotron sources[4], hard X-ray focus optics have been applied widely. For such applications, the reflective mirrors with relatively broad angular range for hard X-ray radiation such as Cu Kα line (λ = 0.154 nm), are required to extend the view field and flux of optics, where bent crystal and single layer metal mirrors cannot be used be- cause of too small grazing incident angle. The periodic multilaye…     

Speeds of sound and isothermal compressibility of ternary liquid systems: Application of Flory’s statistical theory and hard sphere models

Speeds of sound and densities of three ternary liquid systems namely, toluene + n-heptane + n-hexane (I), cyclohexane + n-heptane + n-hexane (II) and n-hexane + n-heptane + n-decane (III) have been measured as a function of the composition at 298.15 K at atmospheric pressure. The experimental isothermal compressibility has been evaluated from measured values of speeds of sound and density. The isothermal compressibility of these mixtures has also been computed theoretically using different models for hard sphere equations of state and Flory’s statistical theory. Computed values of isothermal compressibility have been compared with experimental findings. A satisfactory agreement has been observed. The superiority of Flory’s statistical theory has been established quite reasonably over hard sphere models.      

Elastic “hard” fibers. I.

Elastic “hard” fibers may be prepared from a number of semicrystalline polymers, notably polypropylene, poly-3-methylbutene-1, and polyoxymethylene. These materials show typically a high degree of length recovery from large extensions, a marked, more-or-less recoverable reduction of apparent density on stretching, and the generation of very large amounts of accessible volume and surface area on stretching. Wide- and low-angle X-ray and electron-microscopic observations indicate that the morphological basis for these properties lies in an array of closely packed lamellae of which the normals lie predominantly parallel to the fiber extrusion direction. It is the tilting and splaying apart of the lamellar network which creates the internal volume and surface area on stretching. The long-range elasticity is believed to be distinctly nonrubberlike, as reflected in an insensitivity of mechanical properties to low temperatures, and to arise from bending of the lamellae. This unusual class of materials provides a significant link between macroscopic properties and a particular morphological structure.     

Thermal expansion coefficient of ternary liquid mixture using hard sphere models and Flory’s statistical theory

The coefficients of thermal expansion (α) of ternary liquid mixtures of heterocyclic compounds viz., pyridine/quinoline with phenol in benzene have been evaluated at 308.15, 318.15 and 328.15 K, respectively. A comparative study of thermal expansivity using different models for hard sphere equation of state and Flory’s statistical theory has been made. The computed values of thermal expansivity are compared with the experimental results. The excess values of thermal expansivity have also been computed and utilized to discuss the existence and strength of intermolecular interactions in the ternary liquid system under investigation.     

Magnetization reversal in CoPt-based hard–soft homocomposites

CoPt-based hard–soft sputtered bilayers with (1 1 1) texture have been produced by appropriate heat treatment of the bottom layer. Two samples with different degrees of chemical ordering of the hard layer are compared. The anisotropy of the hard layer determines its robustness against destabilization from the soft one. Detailed measurements of the soft layer minor hysteresis loop features as a function of the magnetic state of the hard layer are proposed as a means to study the nature of interfacial exchange interactions and the mechanism of magnetization reversal. When hard layer anisotropy is not robust enough, the reversed soft layer can induce irreversible changes to the magnetic structure at the interface leading to a decoupling of exchange field from the magnetic state of the hard layer.     

A study of core and valence levels in β-PbO2 by hard X-ray photoemission

The core and valence levels of β-PbO₂ have been studied using hard X-ray photoemission spectroscopy (hν = 6000 eV and 7700 eV). The Pb 4f core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. It is found that intrinsic final state screening is suppressed in the near-surface region. A shift in the O 1s binding energy due to recoil effects is observed under excitation at 7700 eV. It is shown that conduction band states have substantial 6s character and are selectively enhanced in hard X-ray photoemission spectra. However, the maximum amplitude in the Pb 6s partial density of states is found at the bottom of the valence band and the associated photoemission peak shows the most pronounced enhancement in intensity at high photon energy.     

ZrN, ZrxAlyN and ZrxGayN thin films – novel materials for hard coatings grown using pulsed laser deposition

High-quality thin films of ZrN, Zr_xAl_yN and Zr_xGa_yN have been grown by pulsed reactive crossed-beam laser ablation using Zr, Zr-Al and Zr-Ga ablation targets, respectively, and a N₂ gas pulse. The films were characterized for their chemical, crystallographic and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between room temperature and 600 °C. High-quality epitaxial films could be grown on Si (001) at 400 °C, though the crystallinity was disrupted at 525 °C by Si diffusion into the film bulk and the formation of ZrSi₂ crystallites. Films grown on stainless steel were polycrystalline. The ratios of the metals in the alloy targets were in general not equal to those in the films: the Al content in the Zr_xAl_yN films was lower than the target value, which we attribute to differential scattering in the ablation plume. The Ga content in the Zr_xGa_yN films fell with increasing substrate temperature, indicative of re-evaporation of Ga from the substrate surface. Those Zr_xGa_yN films with the highest Ga content, grown at the lowest temperatures, were particularly nitrogen-deficient, which we attribute to the low reactivity of Ga with N₂. The Zr_xAl_yN films had an exceptionally low coefficient of friction (0.20) versus steel and the greatest nanohardness of 28 GPa. Received: 9 November 2000 / Accepted: 14 November 2000 / Published online: 28 February 2001     

Soft processes at the LHC,II: soft–hard factorisation breaking and gap survival

We calculate the probability that the rapidity gaps in diffractive processes survive both eikonal and enhanced rescattering. We present arguments that enhanced rescattering, which violates soft–hard factorisation, is not very strong. Accounting for NLO effects, there is no reason to expect that the black-disc regime is reached at the LHC. We discuss the predictions for the survival of the rapidity gaps for exclusive Higgs production at the LHC.     

Does hard core interaction change absorbing-type critical phenomena?

It has been generally believed that hard core interaction is irrelevant to absorbing-type critical phenomena because the particle density is so low near an absorbing phase transition. We study the effect of hard core interaction on the N-species branching annihilating random walks with two offspring and report that hard core interaction drastically changes the absorbing-type critical phenomena in a nontrivial way. Through a Langevin equation-type approach, we predict analytically the values of the scaling exponents, nu( perpendicular) = 2, z = 2, alpha = 1/2, and beta = 2 in one dimension for all N>1. Direct numerical simulations confirm our prediction. When the diffusion coefficients for different species are not identical, nu( perpendicular) and beta vary continuously with the ratios between the coefficients.