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.     

The distribution of silicon in single crystals of Fe-Si alloys grown from the melt

A method of measuring the distribution of the silicon concentration in single crystals of Fe-Si alloys was elaborated on the basis of determining the relative Seebeck coefficient of these alloys with respect to the reference metal. The dependence of the relative Seebeck coefficient of Fe-Si alloys versus copper on the concentration of silicon was measured in the range of 2–12 weight % Si. The distribution of silicon in a series of single crystals of Fe-Si alloys grown from the melt was also determined.The author thanks the members of the department of the mechanical properties of solids of the Institute of Physics, Czechoslovak Academy of Sciences, and especially the head of the department, Ing. B. esták, CSc., for making it possible to prepare the single crystals and for discussion of the paper. He also thanks Dr. M. Matyá, CSc., for valuable remarks and Ing. Z. Kubita for passing on his experience in the use of the measuring method. He is indebted to members of the analytical laboratory of the State Research Institute for Materials Protection, the analytical laboratory of the Metals Research Institute and the chemical department of the. Institute of Physics, Czechoslovak Academy of Sciences, for careful analyses of the samples.     

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.     

A Metallografic study of the homogeneization quenching of copper

During homogeneization quenching the dislocation density in copper grows up to saturation and the dislocation structure becomes stabilized. This process is realized on quenching into gases and liquids, i.e. at both lower and higher quenching rates. Grain growth is also observed. The dislocation structure formed by cold-working is removed by annealing at temperatures near to the melting point in a time interval shorter than 30 minutes and the dislocation density reaches a stable value, growing with decreasing thickness of the specimen.The authors would like to thank Dr. K. Míek, CSc. (Institute of Solid State Physics, Czechosl. Acad. Sci., Prague) for his comments, Dr. J. Kuera CSc. and Dr. P. Luká, CSc. (Institute of Metallurgy, Czechosl. Acad. Sci., Brno) for critical remarks on the paper and Mrs. J. Zoubková for assistance with the experiments.     

A resistometric investigation of the decomposition kinetics of Al-21·8 at.% Zn solid solution at 276 °C

Under the condition of nearly equilibrium concentration of vacancies, time dependence of the amount of isothermal transformation given byy=R/R _f was investigated whereR _f is the total structural change of resistivity on completion of the whole process andR is the measured resistivity change. The investigation was done on the 21·8 at.% (40·3wt.%) Zn alloy under the condition of relatively low supersaturation of a few degrees centigrade below the metastable _R solvus line. The total transformation involves four kinetic stages: the first two stages correspond probably to diffusion-controlled growth of the _R particles from the supersaturated solid solution and to the ripening of these particles till their conversion to the cubic phase takes place. The last two kinetic stages account analogously for the particles growth and ripening. Both _R and phases were identified by the transmission electron microscopy. When separating the individual stages, the approximation byy=1–exp [–(mt) ⁿ] of the amount of transformationy was used. The approximation allowed to get the starting values of both the time and the change of the structural part of the electrical resistance for individual stages and also to derive the parametersm _i, n_i which had to be redetermined for the individual separated stages. These data made it possible to synthetize the experimental curves ofR andy vs. time for the total transformation.It is a pleasure to thank Doc. Dr. V.Syneek CSc. for stimulating the author's interest in this problem and for providing helpful discussions. I also would like to express my thanks to Ing. P.Bartuka CSc. for the transmission electron microscopic study carried out to identify the particular phases. The author is indebted to Ing.V. íma for the preparation of the investigated alloy and to Mrs. A.Mendlová and Mr. P.Vyhlídka for technical assistance.     

Birefringence in YAlO3∶Ce between 2–5 eV

This contribution presents birefringence spectra for orthorhombic YAlO₃Ce single crystal in the region 2–5 eV. The spectra were measured by means of a reflection method of null ellipsometry and were compared with spectra of YAlO₃:Nd determined from values measured in the region of lower energies (1·1–2·2 eV). We have found that there are differences between the spectra of YAlO₃Nd and YAlO₃:Ce which are most pronounced in thea-axis direction.The author is most grateful to Ing. . Viovský CSc. for helpful discussions during the course of this work and to Monokrystaly Turnov for preparation of the samples.     

Influence of linear elastic stresses on dynamic magnetostriction of cold-rolled transformer steel

The anisotropy of dynamic magnetostriction is investigated without external stresses, in extension, and in compression. Results are obtained expressing the (B) dependence for constant elastic stresses and also — () for certain induction values. Oscillograph traces are taken of the (H) and B(H) hysteresis loops with the specimens under investigation in extension and compression.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 110–115, May, 1977.     

Thermal conductivity of semiconducting amorphous CdGeAs2

The thermal conductivity of amorphous semiconducting CdGeAs₂ was studied between 100 and 300°K. The Debye model was used for the calculation of the mean free path of phonons which was found to be 10 Å at 300°K and was related to the basic structure units of amorphous CdGeAs₂.Thanks are due to Mrs. J. Beránková, Mr. J. Kapar and Mrs. J. Trepeová for the preparation of the amorphous CdGeAs₂ used in this work and for the measurements of the thermal parameters, and to Dr. J. urek and Dr. S. Kolník from the College of Transport Engineering, ilina, for the sound velocity measurements.     

An attempt at a phenomenological interpretation of the influence of a polarizing field on piezoelectric resonators

The change in frequency of quartz piezoelectric resonators in a d-c electric polarizing field cannot be explained merely by a change in the dimensions of the resonator due to the polarizing field caused by the inverse piezoelectric effect and electrostriction. We are forced to admit that the elastic constants also change in a polarizing field. A phenomenological interpretation of the influence of a d-c electric polarizing field on the frequency of quartz resonators is proposed here, based on newly introduced quantities characterizing such a change. In conclusion it is shown in what way the quantities, on which the phenomenological theory is based, can be determined experimentally.

---

, . , . , , . , , .

---

---

The author would like to thank Dr. J. Tichý for carefully reading the paper, for valuable discussion and numerous remarks on style and subject matter, which greatly helped to improve the text. He is also indebted to V. Janovec, C. Sc., for some new aspects and the exceptional interest with which he reviewed the paper.     

Wedge disclinations as models of curvature walls in smectic A liquid crystals

The displacement of layers caused by a wedge disclination and the interaction energy of a wedge disclination pair in a smectic A liquid crystal is determined. Wedge disclinations are used to model and to discuss curvature walls (e.g. chevron structures of twin walls) observed experimentally in smectic A liquid crystals.Dedicated to my teacher Frantiek Kroupa on the occasion of his 65th birthday.     

Evaluation of positron annihilation angular correlation curves and line profiles of compton scattering in noble metals

Angular correlation curveN () as well as the Compton line profile I() of Cu, Ag, Au and Pt have been calculated by the assumption, that the coincidence counting rate and Compton line shift intensity are proportional to the area of cuts through the body defined by the Fermi surface. Parametrical expression of the Fermi surface were employed and the results were used to fit some measured curves on Cu, Ag and Au.The authors are indebted to Prof. P.Ry and Dr. I.Volf for enabling the work, Dr. A. íek for supplying the experimental data for Au, Ag and Cu and J. Sedláek for assistance by programming of numerical evaluations.     

The effect of X-ray coherence on crystalline diffraction

The importance of respecting the coherent properties of X-rays in the physical interpretation of the profiles of the X-ray diffraction patterns is pointed out. Drawing the analogy between Young's experiment and two-atom X-ray scattering, the author applies the elementary theory of coherence, developed for light optics, to X-ray diffraction by a linear atomic lattice. As his considerations concerning the effect of coherence on diffraction by such a lattice are impossible to verify experimentallly, he tests their correctness by spectrographical measurements of the width of an optical grating diffraction line under different coherence and experimental conditions. The paper is dedicated to the memory of Dr. A. Vaíek, Professor of the J. E. Purkyn University in Brno, who died on November 16, 1966.     

Металлографические методы определепия нлотности дислокаци й В монокристаллах германия

, , . , .1) . .     

The effect of microsegregation on the generation of dislocations in zinc single crystals

The applicability of Tiller's considerations on the production of dislocations is proved. The density of dislocations appearing during impurity microsegregation increases with increasing rate of growth as a consequence of the corresponding change in the effective distribution coefficient. The real value of C at the microsegregation boundaries is at least twice as great as the average value of the concentration of impurities in the crystal in question.

---

. , , . C , .

     

Electronic processes andZ centres in NaCl and KC1 crystals

The paper gives the experimental results of the team-work study of coloured pure and Ca doped NaCl and KC1 crystals. The mechanism of the formation ofR centres by coagulation ofF centres and of the formation ofZ centres fromF centres, cation vacancies and Ca ions is discussed. An alternative model forZ ₃ centres is proposed. The possible connections between physical and chemical behaviour are indicated.

---

Z- NaCl 1

NaCl KCl . R- F- Z- F-, Ca. Z ₃-. .

---

---

This work was presented by the courtesy of Prof. R. Maurer at the Symposium on Color Centers, Corvallis, Oregon (1959).

---

The authors wish to express their gratitude to K. Suk, K. Listoová and M. Javrková for carefully carrying out the measurements and I. Kunzlová and L. Nováková for preparing the crystals.     

ПОТОК ЭНЕРГИИ ЧЕРЕЗ Д ИЭЛЕКТРИЧЕСКИЙ ТОНК ИЙ СЛОЙ ПРИ НАРУШЕННОМ ПОЛНО М ОТРАЖЕНИИ

, .

---

Energy flux through thin dielectric film when total reflection is disturbed

It is shown that the energy flux through a thin dielectric film when total reflection is disturbed is brought about by the interference Poynting vector.

     

The propagation of excitation energy in perturbed crystals

The process of the propagation of excitation energy in perturbed dielectric crystals with a weak bond between the atoms having zero permanent dipole moment is studied. It is shown that on certain assumptions this process of propagation can be regarded as the motion of a Frenkel exciton in the electrostatic field of the defect. Frenkel's exciton can be characterized in this case as a neutral polarizable particle having induced dipole moment equal to the change in the induced dipole moment of the crystal during the excitation of one of its atoms.

---

, . , . .

     

Improved absolute liquid scintillation counting of beta emitters

A new method for the absolute determination of the activity of beta emitters in liquid scintillators based on the theoretical shape of their spectrum is described and tested with standardized C14 n-hexadecane.The author wishes to thank P. Jirouek and M. Vitek for their technical assistance.     

ЭЛЕКТРИЧЕСКАЯ ЭКВИВ АЛЕНТНАЯ СХЕМА ЗАТУХАЮЩИХ КОЛЕБАНИ Й СДВИГА ПЬЕЗОЭЛЕКТРИЧЕСКИХ СТЕРЖНЕЙ

n - , - .     

Über die an „Schwachen“ Grenzflächen Entstehenden Kopfwellen

Zusammenfassung In der vorliegenden Arbeit werden die Kopfwellen untersucht, die beim Auffallen einer harmonischen Schall-Kugelwelle auf die Ebene Grenzfläche zwischen zwei flüssigen Medien entstehen. Vorausgesetzt wird, daß die Grenzfläche schwach ist, d. h. daß die Geschwindigkeit der Schallwellen im Medium mit der Erregungsquelle nur um weniges kleiner ist als die Geschwindigkeit der Schallwellen im Medium ohne die Quelle.

---

,

, . , , . . .