Selecting the duration of excitation pulses for an electroluminescent thin-film matrix

The factors influencing the optimum selection of the excitation pulse width of thin-film electroluminescent devices is examined. It is shown that to excite an individual cell, a pulse width of 5–7 sec is sufficient, but to excite the matrix, the pulse width is determined by the independence of the conducting layer and the dimensions of the matrix. Formulas are cited for engineering calculations of the required pulse width.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 59–62, December, 1987.     

Structure of liquid solutions near the critical point

Specific features of the structure of the critical state of binary liquid solutions leading to an anomalous behavior of the Rayleigh line due to a dramatic increase in concentration and density fluctuations are considered. It is shown that an experimental treatment must deal with two fluctuation regions near the critical point of solvent vaporization. In the first region, one can achieve a sufficient degree of accuracy by using theories like selfconsistent field theory. In the second region, which is closer to the critical point than the first region, scaling theory of secondorder phase transitions may be applied. It is found that the anomalous behavior of the Rayleigh line associated with kinetic coefficients is determined by the equilibrium thermodynamic properties and by the radius of fluctuation correlation (rinc). A general theory is developed for calculating thermodynamic potentials, especially the chemical potential and its concentration derivative in the fluctuation region. The results of these calculations are compared with the experimental data briefly described in the paper. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 4, pp. 655–668, July–August, 1998.     

Experimental Verification of the Theoretical Prediction of High‐Temperature Superconductivity in Phases of Titanium Borides TiB k

Theoretical predictions of hightemperature superconductivity (HTSC) in titanium borides, TiBk, have been experimentally verified. These predictions have been reported previously in the form of theoretical phase diagrams. They predicted the existence of HTSC in TiB _k (1.43 < k < 2.57) phases and in TiB_1.5–1.6. An abrupt decrease at 110 K was found on the temperature curve of conductivity R(T) for titanium samples whose surfaces were coated with diffuse layers of depthvariable boride compositions TiB _k . This indicates that the layers include phases possessing HTSC. This behavior of the R(T) curves is explained assuming that the inclusions of HTSC phases have a strong effect on the resistance of the composite materials at T_c. The composition of the boride layers has been investigated by mass spectrometry. Diffuse boride layers were applied to titanium surface by treating its surface with a B₂H₆ + H₂ gas mixture at 610–700°C followed by annealing in vacuum.     

Magnetic properties of two-dimensional Josephson networks: Self-organized criticality in magnetic flux dynamics

The field dependence of the magnetic moment of square (100×100) Josephson networks was examined with the use of a SQUID magnetometer. The field dependence of the magnetic moment was found to be regular with features corresponding to integer and half-integer numbers of flux quanta per cell. At temperatures below 5.8 K, jumps in the magnetization curves associated with the entry and exit of avalanches of tens and hundreds of fluxons were observed. It was shown that the probability distribution of these processes corresponded to the theory of self-organized criticality. An avalanche character of flux motion was observed at temperatures at which the size of the fluxons did not exceed the size of the cell, that is, when a discrete vortex structure occurred.     

Effect of an alternating field on the relaxation of effect of an alternating field on the relaxation of magnetic flux in a Josephson medium

We establish how trapped magnetic flux depends on the frequency and amplitude of an alternating field and how such a field affects the relaxation rate of the flux. We find that the nature of the flux creep changes in the process and that relaxation of the flux stops after the external field is switched off. We examine the dynamics of flux relaxation in a ring in the approximation in which the current density is assumed homogeneous, for various density dependences of the effective vortex activation energy. The critical current density and the vortex activation energy are obtained as functions of the external field strength. Finally, we explain the observed behavior in terms of the different field profiles emerging in the rings. Zh. éksp. Teor. Fiz. 111, 1047–1056 (March 1997)     

Studies of the structure of Ce3+ centers in SrS phosphors

It is found that the shape of luminescence spectra of SrS−Ce phosphors is independent of both the species and concentration of a cofactor F, Cl, Br, or 1 introduced in the form of ammonium halide at least up to 6.5 at.%. The only exception is F, which, when added as a coactivator with a concentration of 2.4 at.% and above, gives rise to new longwave luminescence bands, part from the luminescence of the Ce³⁺ ion. Analysis has shown that this additional luminescence spectrum is similar to the Ce³⁺ spectrum but is shifted towards the longwave region by about 0.14 eV. The luminescence decay time constant (τ=57 nsec) is very close to Br, I, and small concentrations of F, a model is valid according to which the halogen that substitutes for sulfur and the Ce³⁺ that substitutes for Sr are the closest neighbors not to each other, but to a probable compensator of the charge of Sr vacancies. At high concentrations of fluorine some of the F ions are located at interstitial lattice sites in the immediate neighborhood of Ce³⁺, providing compensation for the charge of Ce³⁺ ions and having a marked effect on them. Tartu University, 18, Ulikooli St., Tartu EE2400, Estonian Republic. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 173–178, March–April, 1997.     

On the applicability of the resonance tunneling model for describing conductivity anisotropy in TmBCO single crystals

The temperature dependences of the anisotropy of the resistance in two single crystals of the system TmBa₂Cu₃O_x with oxygen indices x=6.71 and 6.47 are analyzed from the standpoint of the applicability of Abrikosov’s theory [Physica C 253, 53 (1996)]. It is shown that the agreement between theory and experiment improves substantially if in approximating the data, besides resonance tunneling, allowance is made for the contribution of the ordinary tunneling conductivity. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 772–777 (10 December 1996)     

Structure of liquid solutions near the critical point

Specific features of the structure of the critical state of binary liquid solutions leading to an anomalous behavior of the Rayleigh line due to a dramatic increase in concentration and density fluctuations are considered. It is shown that an experimental treatment must deal with two fluctuation regions near the critical point of solvent vaporization. In the first region, one can achieve a sufficient degree of accuracy by using theories like self-consistent field theory. In the second region, which is closer to the critical point than the first region, scaling theory of second-order phase transitions may be applied. It is found that the anomalous behavior of the Rayleigh line associated with kinetic coefficients is determined by the equilibrium thermodynamic properties and by the radius of fluctuation correlation (r_c). A general theory is developed for calculating thermodynamic potentials, especially the chemical potential and its concentration derivative in the fluctuation region. The results of these calculations are compared with the experimental data briefly described in the paper. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 655–668, July–August, 1998.