On the configuration of Guinier-Preston zones in Al-Ag and Al-Zn alloys

An experimental investigation of the short-range ordering in the spatial distribution of isotropic G.-P. zones in supersaturated solid solutions of Ag or Zn in Al is presented. The intensity distribution of the small-angle diffuse scattering can be satisfactorily explained by inter-zone X-ray interferences when using the data on metastable miscibility gaps determined by Gerold for Al-Ag and by Hillert for Al-Zn. The investigation was carried out for a wide interval of annealing temperatures on Al-Ag (6 at. % Ag) and on Al-Zn (11 at. % Zn) samples.The authors wish to express their gratitude to their colleagues of the Institute of Solid State Physics: J. Laek, C.Sc, for valuable discussions and for chemical analyses, V. íma for alloy preparations, and Z. iký for his assistance in the measurements and computations.     

The influence of quenching rate on the kinetics of transformations of metastable phases in the Al-30 wt.% Zn alloy

The effect of quenching rate on the precipitation process in the Al-30 wt. % Zn alloy has been studied by the X-ray diffraction and electron microscopy. No effect has been observed both on the T-T-T curve for the transformation of coherent into semicoherent phase and on the isothermal growth of precipitates of these phases. The significant dependence has been, however, found when the ageing of the investigated alloy led to the formation of incoherent phases. The T-T-T curves for _R and _R transformations are shifted to the shorter ageing times with the increased quenching rate. The slopes of these T-T-T curves yielding parallel straight lines remain unchanged. The role of coherency stresses and of quenched-in strains in the investigated processes is discussed.In conclusion the authors would like to express their appreciation to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. V.Petr and Mr. Z.iký for their help in the heat-treatment and X-ray diffraction measurements of the investigated samples, and to Mr. P.Vyhlídka for the homogeneity control of the Al-Zn alloys.     

The X-ray spectrum of germanium doped with Ga and Sb

The K ₂ emission band as well as the L _1,2 region of the X-ray spectrum of pure germanium and germanium doped with Ga and Sb, resp., are compared. In contrast to papers [1], no changes were found.The authors thank Dr. Z. Trousil for preparing the single crystals, Ing. L. toura, DSc, for the determination of the concentration of the doping elements in germanium single crystals and V. ídová for carefully performing some of the measurements.     

The kinetics of phase transition in systems with nonconservative order parameter

The kinetics of ordering in systems described by the nonconservative order parameter is studied near the second-order transition critical point.On leave fromDepartment of Nuclear Physics and Biophysics, Faculty of Natural Sciences, University of P. J. afárik, Moyzesova 11, 041 67 Koice, Czechoslovakia.     

Effect of structure transformations on the microhardness of Al-15at.% Zn alloy

The ageing of single crystals of Al-15 at. % Zn alloy was studied at the temperature of 205 °C by X-ray diffraction and by measurement of microhardness. A close correlation of individual structure stages with microhardness was found on ageing the alloy.In conclusion the authors would like to express their thanks to Doc. Dr. V. Syneek CSc. for helpful discussion, to Ing. J. Laek CSc. for the careful chemical analyses of the investigated alloy and to Mr. Z. iký and Mr. S. Pazour for assistance in measurements.     

Precipitation sequences and transformation kinetics in the Al-30 wt.% Zn alloy aged below 160°C

The transformation sequences in the Al-30 wt.% Zn alloy aged below 160 °C have been investigated by X-ray diffraction and transmission electron microscopy. The sequence G.-P. zones _R has been observed between 85 and 161 °C, whereas the direct G.-P. zones to-transformation occurs below 85 °C. The identical isothermal growth kinetics of both the G.-P. zones and the _R -precipitates was found. The log-log plots yielding a set of parallel straight lines from 50 to 150 °C indicate no change in the activation energy of growth of both these precipitates. The change in the precipitation sequence led to the change in the transformation kinetics. The T-T-T curves have been measured for the formation of metastable _R -phase and for the completion of ellipsoidal G.-P. zones or of _R to-transformation. The retardation in reaching equilibrium found below 85 °C was associated with the observed change in the transformation sequence. This was explained by the different accommodation of the misfit at the interfaces between G.-P. zones or _R -precipitates and the-matrix.The authors are much indebted to Doc. Dr. V.Syneek, CSc. for stimulating discussions. Our thanks are also due to Ing. V.íma and Mr. P.Vyhlídka for the preparation and careful chemical analyses of the investigated samples. The assistance of Mr. Z.iký and Mr. V.Petr in X-ray diffraction measurements and the heat-treatment of samples is appreciated.     

Influence of Ge and Ag impurities on the thermal conductivity of semiconducting amorphous As2Se3

The thermal conductivity of amorphous semiconducting As₂Se₃ is studied in the temperature range from 100 to 300°K and the influence of germanium and silver impurities is shown. The mean free path of phonons is determined and the observed change of the thermal conductivity is explained by the change of the velocity of sound in amorphous As₂Se₂ containing germanium.Presented by L. toura at the Meeting on Electronic Structure, Optical and Transport Effects in Amorphous and Liquid Semiconductors, Prague, May 1965.The authors are indebted to Dr. J. urek and Ing. I. Turek from the Department of Technical Physics of the College of Transport Engineering in ilina for measuring the velocity of sound in the investigated materials and to Mrs M. Kaparová and J. Trepeová for their help in the experimental work.     

Surface damage in single-crystal Mn-Zn ferrite

The depth of the damaged surface layer and the changes of hysteresis loop caused by surface processing in Mn_0.53Zn_0.35Fe_2.12O₄ single crystal are measured. The results obtained are treated as a consequence of the crystal structure deformation at the surface and coherent limited domain wall movement.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.The author would like to thank Dr. Z. ima, Institute of Physics, Czechoslovak Academy of Sciences, for valuable discussions.     

The room-temperature decomposition of metastable phases precipitated in the Al-Zn alloys at 200 °C

The room-temperature decomposition of metastable phases in the Al-Zn alloys (from 25 to 50 wt. % Zn) was studied by the transmission electron microscopy and X-ray diffraction. Metastable phases, i.e. G.-P. zones, _R-and -phases, were grown at 200 °C and their decomposition into equilibrium -phase at 20 °C was investigated. Ageing times comprised 1 to 999 days.Both the decomposition mechanism and the rate of decomposition of coherent phases were found to be dependent on the particle sizes and their density reached at 200 °C. The local vacancy supersaturation around the -nucleus in a dense system of G.-P. zones leads to an enhanced growth rate of such nucleus and thus to the formation of one large -precipitate at the expense of several neighbouring G.-P. zones. The elastic stress field around this -particle promotes the further nucleation and growth of -precipitates and leads to their gradual spread throughout the matrix. The decomposition of intermediately sized _Rprecipitates results in the development of -precipitates of comparable sizes nucleated on the array of misfit dislocations at the periphery of _R-precipitates. The cooperative effect between neighbouring particles does not influence the decomposition of large _R-precipitated which split then into several smaller -particles. The rate of G.-P. zones or _R to -decomposition increases with the increasing sizes of transition precipitates and with the zinc content of the alloy. The kinetics of to -decomposition was found to be independent both on the annealing time at 200 °C and on the investigated alloy composition. This can be attributed to the constant density of misfit dislocations as nucleation sites for -precipitates along the -matrix interface and to the large mutual separation of -precipitates in all these alloys.In conclusion we would like to express our thanks to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. Z.iký for his help in the X-ray diffraction measurement and to P.Vyhlídka for the careful chemical analyses of the investigated alloys.     

The resonance of domain walls in hematite crystals

The paper contains the results of the observation of frequency magnetic spectra on hematite crystals. Measurements were made in the frequency range from 20 to 90 MHz. The dependence of the spectra on the history of the sample, on the h.f. field, on an external static field and on temperature was studied. The observed spectra are interpreted on the basis of the resonance of domain walls fixed on defects of the crystal lattice. A model is proposed, explaining the observed changes in signal intensity of NMR.On leave from Department of Experimental Physics, A. Mickiewicz University, Pozna, Poland.The authors would like to thank Professor R. Rost and Dr. M. Vichr for the samples and Professor J. Bro and Dr. P. uda for valuable discussions concerning the studied problem.     

ЗАВИСИМОСТЬ ПОЧЕРНЕ НИЯ ФОТОГРАФИЧЕСКОЙ ЭМУЛЬСИИ ОТ ЭНЕРГИИβ-ИЗЛУЧЕНИЯ

, - - . , - , , :³²P,³⁵S ⁹⁰Sr+⁹⁰Y.     

ЛОКАЛЬНЫЕ КОЛЕБАНлЯ ДВУХАТОМНОЙ ЛлНЕЙНО Й ЦЕПОЧКл С ДЕФЕКТАМл

. n : , . npou u , n . n n npocm .     

К процессам в электро дных оБластях в силъноточных кратк овременных электрических разря дах

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On processes in electrode spaces of short-time high-intensity electric discharges

The conditions and causes of the interrupted emission of the vapours of the material of short-time high-intensity electric discharge electrodes are discussed on the basis of earlier and new observations.

     

The effect of iron and silicon on precipitation processes in the Al-30 wt.% Zn alloy aged at 90 °C

The effect of different amounts of Fe and Si impurities in the Al-30 wt.% Zn alloy on both the continuous and the discontinuous precipitation at 90 °C was investigated by transmission electron microscopy and by X-ray diffraction. The results show that the growth of G.-P. zones and _R -precipitates as well as the rate of their transformation into the equilibrium -precipitates are unaffected by Fe and Si impurities. The experiments revealed, however, a significant retardation of the nucleation of lamellar aggregates of equilibrium phases on grain boundaries and a pronounced reduction of the growth of lamellae into the grains by the presence of Fe and Si atoms in the alloy. Their influence on the rate of cellular reaction was attributed to the impurity-drag effect on the cell-boundary motion.In conclusion we wish to express our thanks to Mr. Z.iký for his help in the X-ray diffraction measurements and to Mr. P.Vyhlídka for chemical analyses of the investigated samples.     

ИССЛЕДОВАНИЕ ЭРОЗИЙ НОГО ДЕЙСТВИЯ ИМПУЛЬ СНЯХ ЭЛЕКТРИЧЕСКИХ РАЗРЯ ДОВ С СЛАБЫМ ТОКОМ

50–100 , 1–2 1–10 . - . - . , , - . -.     

Interacting spinor and scalar fields: Exact self-consistent solutions in Bianci I space

Exact self-consistent solutions of the equations that describe a system of interacting spinor and massless scalar fields with the interaction Lagrangian L_int=_,^,(S), where (S) is an arbitrary function of the invariant S=, are obtained in Bianci I space. The possibility of excluding the initial singularity is studied for the case of a power-law function (S), and isotropic expansion of the space as t is established.Russian University of International Amity. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–58, July, 1995.     

Anti-parallel ferroelectric domains in surface space-charge layers of BaTiO3

It is shown on simplified models of a surface space-charge layer of a single crystal of BaTiO ₃ that in the surface region, in which the direction of the electric field is opposite to the direction of spontaneous polarization inside the crystal, anti-parallel domains can exist. The dimensions of these domains are determined. The use of the results obtained is proposed for interpreting the microrelief of the etch figures and for explaining the different phases of the polarization reversal process of a single-domain single crystal of BaTiO ₃.

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BatiO₃

BaTiO₃ , , , . . BaTiO₃.

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The author would like to thank J. Kaczer, Z. Málek and V. Dvoák of the Institute of Physics, Czechoslovak Academy of Sciences, for valuable remarks on this paper and H. Havlíková for carefully carrying out the numerical calculations.     

Laser collimation of an Fe atomic beam on a leaky transition

We report results of the first laser collimation of a thermal beam of Fe atoms on the leaky ⁵D₄ ⁵F₅ transition, with both parallel linear ^xx and crossed linear ^xy laser polarization configurations. The measured atomic beam divergence is compared to a rate-equation model and a quantum Monte Carlo model. The experimental values for the divergence are limited by the finite laser line width, which is comparable to the natural line width of the Fe atom. In general, flux decreases with higher intensities, showing the effect of the leaky transition. At the best beam collimation _RMS = 0.17 mrad, which is for a detuning of = – and a saturation parameter of s = 6, the flux decreased to approximately 70%. Highest flux was measured for a detuning of = –2 and s = 4, reaching 135% of the uncooled value. From our measurements we estimate the total leak rate to be 1/(240 ± 40), which is in good agreement with the literature value of 1/244. The crossed linear polarization configuration is the better choice, with a slightly better collimation but the same atomic beam flux. Plugging of the largest leak would increase the flux to at least 80% of the closed transition value, resulting in better contrast for atom lithography.     

Highly oriented thin oxide films on single crystals of Fe-Si alloys

Under certain oxidation conditions, highly oriented oxide films grow on single crystals of some Fe-Si alloys. A typical two-phase film of this kind was studied in order to reveal the orientational relationships between-Fe₂O₃ and Fe₃O₄ on the (001) surface of the substrate. The orientational relationships were determined from reflection high-energy electron diffraction patterns where reflections from both oxides were present.The authors are indebted to Ing. B. esták and Ing. S. Kadeková who made possible the preparation of single-crystalline samples of Fe-Si alloys in the Institute of Physics, Czechoslovak Academy of Sciences; to Dr. M. Rozsíval (Institute of Solid State Physics, Czechoslovak Academy of Sciences) who enabled the authors to use the electron diffraction apparatus; and to Dr. A. Línek (Institute of Solid State Physics, Czechoslovak Academy of Sciences) for helpful discussion.