Far infrared properties of SbSI-SbSeI mixed crystals

Far infrared reflectivity of eight SbS_1–x Se _x I mixed single crystals was measured in 50–400 cm^–1 region in polarized light at 25 and –170 C. While the low-frequency ferroelectric mode shows clear one-mode behaviour the second B_1u mode in 126–180 cm^–1 region shows two-mode behaviour. The existence of local and gap modes in this case is discussed.The author thanks ing. K.Nejezchleb from College of Chemical Technology in Pardubice for the crystals, L.Novák for helpful discussions, Z.Híová for computations and N.Dvoáková for help and figure drawing.     

Growing and morphology of crystals of adenine sulphate

Single crystals of adenine sulphate (C₅H₅N₅.H₂SO₄, molecule weight 233.19) of size 10 to 16 mm have been grown using the method of cooling the solution. Both the apparatus and technology are described. The chemical composition of the crystals and the crystal class of the orthorhombic system (2/m 2/m 2/m), by means of an optical double-cirle goniometer have been determined.The author wishes to express her thanks to Miss H.Rajmonová and to RNDr. H.íchová from the Department of Solid State Physics of the Faculty of Mathematics and Physics for the measurements of Laue diffraction patterns, and to Dipl. Ing. L.Rychnovsky from the Research Institute of the Industry of Fats for the analyses on the gas Chromatograph.     

Photoelectric properties of linear oligoaniline derivatives

Dark conductivity and photoconductivity were measured on polycrystalline layers and single crystals of the arylamine type compounds. The photoconductivity process is largely affected by the effects of trapping of the charge carriers followed by their thermal releasing from traps. The activation energy of photoconductivity is determined by the depth of the traps, similarly to the activation energy of the dark conductivity at lower temperatures. At laboratory temperatures and higher ones the activation energy of the dark conductivity is determined by the position of the Fermi level.The author is indebted to Dr B.Sedláek and Dr J.Honzl for their interest, to Dr K.Ulbert for support, valuable discussion, and critical reading of the whole paper, to Dr K.Vacek for discussion and surveying the paper, to Dr M.Tlusáková for sample preparation, to Mr J.Obrda M. Sc. for assistance in measurements of the photoconductivity of single crystals, and to Mrs V.Berdychová and Mrs J.Vaková for technical assistance.     

Theg-factor in pure polycrystalline iron

In order to obtain exact values of the spectroscopic splitting factor (g-factor) in pure polycrystalline iron, measurements of ferromagnetic resonance and antiresonance in thin foils have been performed in parallel configuration at frequencies 26, 36 and 70 GHz, at room temperature. The results confirm the independence of theg-factor on frequency in the given range and yield the valueg=2·088±0·008, in good agreement with measurements of single crystals and with corrected data of other authors.The author wishes to thank Dr. K.Lázár and Prof. K.Tompa (Central Research Institute for Physics, Hung. Acad. Sci., Budapest) for the kind supply of the iron foil together with information concerning the preparation and chemical analysis of the material. Stimulating discussion on the results of measurements with Dr. R.Gemperle and Dr. J.Paes (Institute of Physics, Czech. Acad. Sci.) is highly appreciated.     

The role of nickel in stimulated processes in NaCl

The influence of nickel impurity upon thermostimulated (ionic conductivity, TSE, TSL, TOB) processes and absorption, ESR and luminescence of sodium chloride doped with different concentrations of nickel and irradiated with different doses of X-rays is studied. It is shown that both the concentration of nickel and the dose of X-radiation play an important role. Further, the form of TSE-, TSL- and TOB-curves in NaCl-Ni changes, to a certain degree, very similarly as in case of calcium.The authors wish to express their appreciation to Dr. M.Lébl for preparing the crystals, Dr. I.Velická for the polarographic analysis, Ing. E.Mariani for the measurements of conductivity, to K.Dolealová, E.Linhartová and I.Sváková for careful measurements and elaboration of experimental results, to L.Berkes for the ionic conductivity measurements and to K.Raksányi for the purification of the fundamental NaCl material.     

Internal conversion of the 84·23 keV transition in170Yb

The conversion coefficient _K=1·48±0·07 and the total conversion coefficient = =8·05±0·2 have been determined by means of the 4 scintillation counter.The authors are obliged to Mrs.Boukalov, Mrs.Vladykov and MissStíteská for the assistance in the elaboration of this paper.     

X-ray topographic observation of lattice defects in TGS crystals

Lattice defects in TGS single crystals have been studied using both transmission and reflection X-ray topography. Dislocations of different types have been observed and the Burgers vectors of most of them have been found. Volume defects, their shape and distribution have been investigated and suggestions for the explanation of their character are given. Interactions between these defects and between them and ferroelectric domain walls are discussed.The authors would like to express their thanks to Drs. Z.Málek and B.esták for stimulating discussions. They are grateful to Prof. A.Authier for showing them some results of his X-ray topographical study of the same crystals before their publication. They are also indebted to Ings. F.Moravec and J.Novotny for providing the crystals and to Ing. J.Brádler for his help in taking the X-ray topographs.     

Properties of LiZn x V2−x O4 and LiMg x V2−x O4 mixed oxides

The phase composition of the mixed oxides, series LiMe _x V_2–x O₄, where Me=Zn, Mg, was studied using X-ray analysis. The minor phases present in the investigated samples together with the basic spinel phase were determined as Li₃VO₄ and Zn₂V₂O₇ or Mg₂V₂O₇ respectively. Their presence is caused by the tendency of tetravalent vanadium ions to the disproportionation. For the compositionsx=0·375 were determined the quantitative phase compositions. The lattice constant of the spinel phase is linearly changing according to Vegard's rule, for the zinc series in the range 0x0·375 and for the magnesium series in the range 0xs0·25. Further substitution in magnesium series caused tetragonal deformation of the cubic spinel lattice.The author is indebted to Dr. A.Bergstein for helpful discussions and to Mrs. E.Hrubá for technical assistance.     

Some physical properties of KCl+Pb2+ crystals

This paper presents the results of measurements of the mechanical and electrical properties of as-received pure and lead-doped crystals of potassium chloride. The critical resolved shear stress of the crystals obeys the Franks relationship in the whole concentration range. In addition, the correlation between ₀ and the Vickers hardness numberH was found and the equation is of the form ₀=k (H–H ₀). The solubility of Pb²⁺ in as-received KCl crystals was observed, from measurements of the electrical conductivity, to be low—the successive saturation of the solid solution started already in an environment of 5 mole ppm in agreement with data from the mechanical measurements. The density of cation vacancies and their mobility were represented by the following euqations ₁ T=6·25×10⁴ exp(–·75/kT) cm² K/volt. sec,n ₁=6·95×10²³ exp(–2·12/kT) vacancies/cm³ The value of 0sd46±0·02 eV was found as a rough estimate of the association energy.The authors wish to express their thanks to Professor Dr. J. Z.Damm and Ing. E.Mariani for their stimulating interest in the present work.     

Microwave heating of electrons of a dense plasma column at frequencies higher than electron cyclotron frequency

In this experimental study the absorption of plasma waves, excited in a dense plasma column, was investigated and the localization of the regions of efficient heating of electrons were determined in a broad range of parameters: 1>_ce/>0·1, 0·3<n/n _UH <25, 10^–5<v/< <10^–3. The heating of electrons near the second electron cyclotron harmonic was investigated in greater detail.We are grateful to the members of the Staff of the Institute of Plasma Physics Drs. P.unka, R.Klí'ma, V.Kopecký, J.Musil for discussion of the results. We also thank Drs. J.Musil, F.áek for the help and advice in the early stages of experimental work during construction of different diagnostic devices. Our thanks are due to the director of the Institute Dr. J.Váa for encouraging support of this experimental program.     

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.     

On the role of water in some optical properties of alumino-phosphate glasses containing manganese

Optical absorption in broad frequency range (150–5×10⁴ nm) and thermoluminiscence (TL) of the manganese doped alumino-phosphate glasses with two modifiers (Mg, Sr) were measured. It was found that with prolonged melting time the absorption bands at 3·1 m, 5·3 and 5·9 m decrease, new band at 4·2 m appears and that one in UV at about 235 nm increases. Simultaneously the solubility of the glasses in water increases. At longer melted and irradiated glasses the band of electron centres at 210 nm increases while that one of hole centres at 550 nm decreases. These changes are due to the escape of water bonded on two non-bridging oxygens, as well as to the hydrolysis of the melt and oxidation of divalent magnanese. The role of modifiers is also pointed out.The authors would like to express their gratitude to Dr. L.Pajasov á, E.Linhartová and M.Frýbová for careful measurements and PhMr K.ermák for the performing of solubility measurements.     

Effects of covalency on magnetic properties of tetrahedral V4+ ion in garnets

The theory of covalency is applied to the discussion ofg-factors and hyperfine constantsA of a V⁴⁺ ion in tetrahedral sites in garnets Ca₃X₂Ge₃O₁₂ with X=Sc, Al, Lu, In, and NaCa₂. Mg₂V₃O₁₂, Ca₃Sc₂Si₃O₁₂, Sr₃Sc₂Ge₃O₁₂. The site symmetry is S₄. Coefficients in LCAO-MO wave function and the Fermi contact interaction constantx are determined by an iterative procedure from experimental data. The spin-orbit coupling coefficient _d and radial average r ^–3 are deduced from the condition of solvability of four equations: overlap and charge-transfer integrals are also determined.The author is grateful to Dr. P.Novák for many valuable discussions on the subject and Dr. J.Jokl from the Institute of Macromolecular Chemistry of Czechoslovak Academy of Sciences for optical measurements.     

Luminescent properties of A1N activated by europium

The concentration and temperature dependence of emission and excitation spectra was measured on powder A1NEu phosphors. It was shown that A1N: Eu has two luminescent modifications which depend on the activator concentration. At low activator concentration the wide emission band is found in the blue-green region, while at high concentration it is in green region. The excitation spectra of A1NEu consist of wide bands extended from 40×10³ cm^–1 to 22 × × 10³ cm^–1. The emission and excitation spectra are interpreted as transitions between energy levels of Eu²⁺ ions (4f⁷4f⁶ 5d transitions). The structure of the Eu²⁺ luminescent centres and the temperature dependence of luminescence are discussed.The authors thank Dr. M.Polcarová for the RTG measurements and Mrs. I.Míková for the spectral analysis of the A1N: Eu samples. The authors are also grateful to Prof. M.Trlifaj, Dr. J.Pastrák and Dr. J.Kubátová for valuable discussions.     

Vavilov-Cherenkov radiation in the biaxial triglycine sulphate crystal

Some properties of the Vavilov-Cherenkov radiation in the biaxial triglycine sulphate crystal have been analysed. The radiation properties have been studied for the cases of protons moving along the main three dielectric axes. The measurements were performed with the 660 MeV proton beam.A quantitative agreement of experiment with Muziká's theoretical calculations on the directional properties was observed. In all the cases a qualitative agreement concerning azimuthal distribution of the radiation intensity of the extraordinary waves of both polarities as well as concerning the polarization properties predicted by Obdrálek's formulae has been obtained.Dedicated to the Memory of Professor . Muziká.On leave from Department of Nuclear Physics, Comenius University, Bratislava, Czechoslovakia.The authors are grateful to Prof. V. P.Dzhelepov, Director of the Laboratory of Nuclear Problems, to Prof. L. I.Lapidus for support of the experiment as well as to Prof. L. M.Belyaev and I. V.Gavrilova (the Institute of Crystallography of the USSR Academy of Sciences) for supplying triglycine sulphate crystals, to J.Obdrálek (Charles University, Prague) for fruitful discussions and helpful advice, to Dr. R.Pose for assistance in obtaining negative colour film, to E.Janikova and R.Janik for great assistance in the experiment.     

Visible and near-infrared absorption of LiCl crystal with divalent nickel

Absorption spectra of thed-d transition in the LiCl: Ni²⁺ crystals were measured. It was deduced therefrom that the absorption bands belong to the octahedrally coordinated divalent nickel like in the other alkali chloride crystals of NaCl type. The observed structure connected with³A_2g ³T _1g ^/a ,¹ E _g transitions has been discussed.Cukrovarnická 10, Praha 6, Czechoslovakia.We are grateful to J. Trnka for polarographic measurements of the concentration of Ni²⁺ in samples measured and to A. Bohun for discussions.     

The CNDO-MO study of oxygen impurity states in AlN crystal

Deep levels due to oxygen impurity have been theoretically studied by the quasimolecular approach. The calculation of the orbital spectra was performed using the CNDO/2 method. Some important quantities (transition energies, width of valence band, effective charges etc.) were estimated. The results obtained agree qualitatively well with experimental data but quantitatively are still about 20% in error. Some reasons for the above discrepancy are briefly discussed.The authors are very grateful to Dr. J.Kubátová and Dr. S.Paesová for helpful discussions of the experimental investigations of aluminum nitride and to Dr. J.Pastrák for his interest in this work and discussion of results.     

Internal friction in cd+zn alloy single crystals

Internal friction measurements were used for the examination of Cd + Zn alloy single crystals. It was established that the interaction energy between solute Zn atoms and dislocations in basal planes is 0·12 eV.The authors thank Dr. P.Luká, CSc., for valuable discussions.     

A study of the solid state-gaseous phase equilibrium in CdSe and its application to the growing of single crystals from the gaseous phase by Frerich's method

The equilibrium between the solid state and the gaseous phase of the semi-conducting compound CdSe is investigated. This is a study of two equilibrium reactions CdSe(s)Cd(g) + + (1/2) Se₂(g) and Se₆(g)3 Se₂(g) as a function of the temperature. The results were used to estimate the optimum conditions for the growing of CdSe single crystals from the gaseous phase by Frerichs' method. The basic electrical and optical properties were then measured on the crystals. In conclusion the results of the experiments are evaluated and compared with those of other authors.In conclusion, the authors thank Dr. E. Klier and other members of the department for much valuable advice and remarks, and laboratory assistants O. Kundrátová and J. Rejna for help in the work.     

On the interpretation of the thickness dependence of the coercive field of BaTiO3 single crystals

It is shown in the paper that the thickness dependence of the coercive field of unetched and of successively etched BaTiO₃ single crystals can be explained by the presence of a ferroelectric surface layer with decreased permittivity. In contrast to the Merz model [1], which considered a homogeneous layer, the authors assume that the permittivity inside the layer gradually decreases in the direction to the surface. By using experimental results it has been found for the constant, characterizing (according to [1]) the thickness dependence of the coercive field of unetched crystals, that=1.6 V, which is in satisfactory agreement with experiment.The authors thank V. Dvoák C.Sc, J. Fousek C.Sc, and Z. Málek C.Sc. for stimulating discussions.