Study of the influence of iron and lanthanum oxides on the band structure of Pb(Zr,Ti) O3

The measurements of diffuse reflectance spectra in the range of 400; 2500 nm and of photoacoustic spectra in the range of 350; 800 nm were used for the study of the influence of iron (III) oxide and lathanum oxide additions on the band structure of polycrystalline lead zirconate — lead titanate solid solutions. The molar ratio of zirconium and titanium in the studied solid solutions was 60 40, and the concentrations of the dopants werex FeO_1.5, andy LaO_1.5, werex 0; 0·05 mol, andy 0; 0·10 mol, respectively. The diffuse reflectance spectra were expressed in terms of the Kubelka-Munk function values versus incident electromagnetic radiation energy. These dependences were decomposed into partial absorption bands using a computer. Transitions of charged carriers between energy levels or bands which differ mutually by the energy of 0·9, 1·2–1·3, 1·6, 1·65–1·7, 2·4–2·5, 2·75–2·8, 2·9–3·2, 3·4–3·8 eV, were identified. Their intensities depend on the concentration of Fe and/or on La in the Pb(Zr_0.60 Ti_0.40) solid solutions.The authors are very grateful to Mrs. Iva Havlasová, Vra Andrsová, Ing. Jan Netuka, and Mrs. Liana Karlíková from the first authors' institute, for their technical assistance.     

Electron emission from sandwich cathodes with mica dielectric layer

The measurements of the leakage and emission characteristics of sandwich cathodes with a mica dielectric layer are described. The thickness of the mica varied between 0.6–11 m, the thickness of the upper gold electrode was about 200 Å. The leakage characteristics were well reproducible, the leakage current density was 10^–11–10^–5 A/cm². The emission characteristics had an exponential form, the emission currents were quite unstable. In some cases the transmission coefficient attained much greater values than for other sandwich cathodes (0.5). At higher applied voltage spontaneous slow relaxation oscillations of the emission current were observed. A qualitative interpretation of the observed phenomena is made.Presented at the 13th Field Emission Symposium in Ithaca (New York), U.S.A. in September 1966.     

Lasing near 200 Å with neon-like zinc and lithium-like sulfur

In this paper we present the recent results obtained on X-ray lasers with the new facility of LULI (Palaiseau, France). As regards the study of collisional-excitation pumping we show that the J=0–1 line of neon-like zinc, at 212 Å, exhibits a surprisingly large gain coefficient of 4.9 cm^–1. A detailed comparison of the time-dependent intensities of the J=0–1 and the J=2–1 line at 267 Å leads to the conclusion that these two lines are not emitted in the same region of the plasma. On the other hand we performed a theoretical and experimental study of 5g-4f lasing line of lithium-like sulphur at 206.5 Å. For the first time, in the case of plasma recombination pumping, we did not observe any reduction of the gain coefficient when the plasma length is raised from 1 cm to 2 cm. From numerical simulation this is likely due to radiation trapping and similar processes having much less influence on 5g-4f population inversion than on previously observed lithium-like lasing transitions. These results show that large gain-length values should be obtained with 0.5 kJ driving laser pulses.     

Crystallization temperatures of thin Co−Zr amorphous alloy films from electron diffraction

The transformation of amorphous thin alloy films of Co–Zr to the crystalline state was observed with an electron microscope in the diffraction mode. This investigation elucidates the crystallization temperatures,T _x , of thin films as opposed to theT _x presented for thicker samples; usually melt-quenched in the thickness range of 20–50 m. TheT _x of the thin films are compared also with theT _x for sputtered alloys of Co–Zr at 5 m.     

Chemical structure and internal diffusion within polymer chains in the melt

The single chain dynamics of polydimethylsiloxane in the melt is studied by means of quasielastic neutron scattering. For this polymer the wave vector range 0.03 Å^–1q0.30 Å^–1 covers the regime of universal modes as well as local diffusive processes. A model is described which incorporates the specific chemical structure of the macromolecule and allows to interpret our data in the full wave vector regime. The only parameter which enters the model, the monomer diffusion constantD _m, is found to be (1.2±0.2)·10^–5 cm²s^–1.     

Compton mechanism of γ-quanta emission in the extremely inelastic scattering of electrons by hadrons

The Compton mechanism at the emission of -quanta, in the extremely inelastic scattering of charged leptons by hadrons is investigated using the quark-parton model. The cross section of the e^– + qe^– + q + (q-quark) process, in which two particles are recorded in the final state corresponding to the Compton mechanism, is calculated. The structural functions of the extremely inelastic scattering of electrons by nucleons are obtained for this mechanism. A violation of the gauge invariance of extremely inelastic scattering due to consideration of the radiational corrections is pointed out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 9–13, January, 1982.     

Luminescence of AgCl excited by u.v. laser light

The spectral distribution and decay of the blue-green luminescence of AgCl has been measured at very low temperatures, using u.v. laser excitation. A structure was observed in the emission band at 77°K. The decay consists of three processes: a) a very fast process which follows the laser pulse (10^–8 sec), b) a fast exponential process which is also observed with low intensity u.v. excitation,(10^–4–10^–5 sec) and, finally, c) a slow exponential process (seconds).     

Decay of the Bethe–Salpeter Kernel and Bound States for Lattice Classical Ferromagnetic Spin Systems at High Temperature

We consider lattice classical ferromagnetic spin systems at high temperature (1) with nearest neighbor interactions and even single-spin distributions (ssd). Associated with each system is an imaginary time lattice quantum field theory. It is known that there is a particle of mass m–ln in the energy-momentum spectrum. If s ⁴–3s ²²<0, where s ^k is the kth moment of the ssd, and is sufficiently small, we show that in the two-particle subspace there is no mass spectrum up to 2m. For >0 we show that the only mass spectrum in (m, 2m) is a bound state of mass m _b=2m+ln(1–)+O(), where =(+2s ²²)^–1. A bound on the decay of the kernel of a Bethe–Salpeter equation is obtained and used to prove these results.     

Compatibility of higher rho-resonances with the pion form factor data

A realistic pion form factor model respecting the usual fundamental principles supplemented by reasonable assumptions is constructed by means of conformai mapping having some specific uniformization properties. The model includes the contributions of higher rho-resonances without any conflict with analyticity, provides a certain flexibility for the asymptotic behaviour and depends just on the physical parameters. The best fit of all existing data is achieved with(770),'(1600) and the asymptoticst ^–3/2. The predicted values of the pion charge radius, P-wave isovector scattering length, as well as theI=J = 1 scattering amplitude at the experimental measurable region coincide with the world averaged data.Dedicated to the 30th anniversary of the Joint Institute of Nuclear Research.The authors are indebted to Prof. V. A. Meshcheryakov, Dr. S. B. Gerasimov and Dr. D. Krupa for many stimulating and illuminating discussions.     

Expansion of the frequency criterion of absolute stability for controllable systems with one nonlinear nonstationary element

It is demonstrated that for nondegenerate systems having a nonstationary nonlinearity the frequency condition k^–1 + Re W(i) 0 (k < ) ensures exponential absolute stability.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 3, pp. 319–322, March, 1972.     

Reflection of superlong waves from the terminator in the earth — Ionosphere waveguide

Results are offered of an experimental study of reflection of vlf radio signals from the day-night transition region of the earth-ionosphere waveguide. The reflected signal was distinguished and detected by the Doppler shift in its frequency produced by terminator motion. Reflection coefficient values on the order of magnitude of 10^–2–10^–3 were determined. Estimates were performed which indicate that the observed reflection cannot be described within the framework of smooth change of the waveguide parameters in the terminator region. In correspondence with this, the statistical problem of vlf wave scattering by terminator roughness was solved. Using transition region inhomogeneity characteristics consistent with data in the literature, calculated reflection coefficient values close to those observed experimentally were obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1582–1590, November, 1978.In conclusion, the authors wish to express their sincere gratitude to B. N. Gershman, I. M. Fuks, and V. D. Freilikher for their study of the preliminary draft of the study and many valuable suggestions, and to their colleagues in the radiophysics faculty of at Leningrad State University for participating in the evaluation of the results.     

Optical study of praseodymium doped yttrium aluminium garnet

The absorption and fluorescence spectra of YAG crystals doped with praseodymium at 1% level are investigated through dye laser spectroscopy. The spectra can be interpreted as evidence for at least three series of crystallographic sites for Pr³⁺, but only the transitions which involve the ground state are really complex, that is multi-sites like. It is suggested that an electronphonon interaction occurs through resonance with peaks in the density of phonon states and ground state Stark levels in the range 350–750 cm^–1. This creates new vibronic states and the appearance of a large number of lines for transitions involving ground state especially if laser excitation of the fluorescence is used.Presented at the International Symposium on Solid State Chemistry, October 28–31, 1986, Karlovy Vary, Czechoslovakia.     

Infrared properties of quartz fibres

The IR properties of micron-size amorphous SiO₂ fibres have been investigated between 400 cm^–1 and 1400 cm^–. For the single scattering size and shape effects have been measured and compared with theory. The observed diffuse reflection of quartz wool can be explained qualitatively by the Kubelka-Munk theory for multiple scattering.reported at the 5th International Conference on Infrared and Millimeter Waves, October 6–10, 1980     

Structural influence on the 2D-conductivity of thin Au films

Thin gold films (60Å–500Å) are prepared simultaneously onto carbon coated quartz- and NaCl-crystals at different substrate temperatures (5 KT300 K) in uhv. For the Au-films condensed onto the quartz substrates the temperature dependence of the electrical resistivity is measured between 1.7 K and 300 K in situ. The corresponding Au-films condensed onto NaCl are removed and investigated in an EM. The observed hole and channel structures are related to the 2D-conductivity behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Temperature dependence of the effective work function for the BaO - W system

The temperature dependence of the work function has been examined for the BaO-W system for degrees of coating less than 1 and about 1 in the range 700–1400 °K; it is found that a monomolecular film gives a negative sign of this coefficient in this temperature range ( /T 10^–4 –10^–3 eV/deg). At 1000–1200 °K, the temperature coefficient is almost zero, while at 1200–1400 °K there is a positive value. If the covering is less than monomolecular, the sign is positive throughout the entire temperature range (/T 10^–4 eV/deg).Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 65–70, September, 1971.We are indebted to N. I. Éngovatova for direct assistance with the measurements, and to V. Rumyantsev for advice.     

Exchange-coupling across SiO

Strongly temperature-dependent ferromagnetic exchange coupling is observed between Fe films separated by an amorphous SiO barrier. Heating reversibly enhances the coupling strength which monotonically decreases with increasing SiO thickness. AtT=40K the coupling disappears for d_SiO20Å whereas at room temperature it persists up to a barrier thickness of 60 Å. The coupling strengthJ is determined by externally compensating the exchange field of samples grown on an antiferromagnetically biased Fe/Cr/Fe structure. It amounts toJ2·10^–6 J/m² for a sample with d_SiO=25 Å atT=300K. As a tentative explanation we propose that impurity or defect states within the large mobility gap of SiO carry the magnetic interaction across the insulating barrier.     

Photoconductivity of highly excited A IV B VI thin films

We report the results of picosecond photoconductivity measurements in photosensitive electrolytically deposited PbS and vacuum evaporated PbTe polycrystalline films. We determine Auger recombination to be the prevailing carrier recombination mechanism in highly excited PbTe and PbS films and found Auger coefficients _A5×10^–28 cm⁶ s^–1 for PbTe and _A5.3×10^–29 cm⁶ s^–1 for PbS for carrier concentration changes N>10¹⁸ cm^–3. The results indicate that the low mobility values are controlled by intergrain carrier scattering. We have studied the thermal annealing influence on picosecond photoconductivity of the films.     

On the memory functions in simple classical liquids

The relation between the two memory function formalisms for correlation functions in classical liquids is discussed. It is found that the kinetic equation formalism of Duderstadt and Akcasu with a simple exponential memory function can account for the double Gaussian form of the memory function in the generalized-hydrodynamics approach. The former therefore gives reasonably good results for the coherent scattering function S(k, ), as is shown for the case of liquid Rb at 315 K in the range 1.25 k 5.5 Å^–.     

Distribution of “structural” elastic stresses in substrate under a thin epitaxial film

A calculation is performed of the structural stresses in a substrate that are due to the mismatching of the lattice parameters of the film and the substrate. By assuming the film to be sufficiently small (h 0.01 p, where p is the distance between the mismatch dislocations), we simplify the initial system of equations for an equilibrium elastic medium, and obtain an exact solution for the parabolic model and an approximate solution for the Peierls-Nabarro model. The analytic and numerical analysis of the solution for the Ge-GaAs system shows that for a depth z 0.05 p the distribution of stresses is not very sensitive to the choice of model and the size of the shear modulus at the separation boundary. Therefore, despite the fact that there are at present no reliable methods for determining , the obtained solution allows us to investigate the distribution of stresses in the depth of a substrate by using a small digital computer.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 77–81, June, 1986.