Localization and symmetry of valence states in GaS

The valence electron states of layered semiconductor GaS were studied by polarizedK X-ray emission bands. The polarized gallium and sulphurK bands were calculated and GaK₂-bands were measured by the two crystal spectrometer. In the calculations the self-consistent pseudo-potential method was applied. Thep _x ,p _y p _z -character and localisation of valence electron states were identified. Comparison with the results of controversial interpretation of photoemission and tight binding calculations were done and analysed in detail.We are indebted to J. Mikkelsen from Xerox Research Center in Palo Alto for kindly sending us the GaS single crystals.     

Experimental evidence of the delocalized 3D-electrons in the “cations” OF ZnSe and CuBr

For the last members of the isostructural series Ge, GaAs, ZnSe and CuBr the partial delocalization of the “cation” 3d-electrons takes place, caused by their interaction with the valence band. By measuring the X-ray Kβ_{2, 5}-emission bands in ZnSe and CuBr this fact was proved experimentally. In addition the K_β2-emission bands of CuBr clearly show that the valence electrons are localized most of the time on the Br-atoms. The ZnK_α2 emission bands measured in Zn, ZnSe, ZnO and ZnF₂ give information about the 3d-electrons of zinc and the valence band of these substances.     

Single crystal diffraction patterns of germanium. Part II

The rocking curves of Ge (111), (220), (333) for CuK ₁ radiation were measured by means of the triple-crystal diffractometer. Perfect silicon single crystals, cut parallel to the (111) plane were used in the monochromator part of the triple-crystal diffractometer. The results prove the suitability of such a monochromator for studying diffraction patterns.

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. II

(rocking curves) (111), (220), (333) CuK ₁ . , (111). .

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In conclusion the authors thank A. Haruý for preparing the germanium single crystals and they are indebted to V. Smutná and A. Irra for the care with which they carried out various tasks.     

Double crystal spectrometer with relatively high vertical divergence and instrumental distortion of X-ray spectra

The problem of vertical divergence on the double-crystal spectrometer is treated, both theoretically and experimentally. It is shown that, even in the case of finite vertical divergence, one may get the resulting profile of the measured spectral line as a convolution of the true spectral line and the instrumental smearing function. The general method of calculating this smearing function is given. Further, the influence of the vertical divergence is separated, and some general features are derived.In the experimental part, a double-crystal spectrometer for the fluorescent method of excitation and the precise adjustment of the instrument is described in detail.The theoretical formulas concerning instrumental smearing, the dependence of the peak intensity and the shift of the maximum on the vertical divergence are verified experimentally.     

ВЛИЯНИЕ ПОЛНОГО ОТРА ЖЕНИЯ НА ДИАФРАГМЕ СОЛЛЕРА НА РАЗРЕШАЮШ УЮ СИЛУ РЕНТГЕНОВСКО ГО СПЕКТРОГРАФА

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A contribution to the theory of the triple crystal diffractometer

The first part of the paper gives a general equation for triple-crystal arrangement with perfect crystals on the assumption that the third crystal is rotated. It is shown that in the case of perfect crystals the shape of the reflection curve is practically independent of the vertical divergence. The case of mosaic crystals is also solved and the possibility of rotation by other than the third crystal is considered. A method is proposed for investigating the imperfection of a crystal which is different from methods used up to now. The paper is supplemented by some experimental results.

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Piezoelectric properties of tetragonal single-domain Mn-doped NBT-6 %BT single crystals

We report a study of properties of Mn-doped NBT-6 %BT single crystals. We show that tetragonal single-domain states can be stabilized by poling along a [001] direction. For carefully prepared crystals, the piezoelectric coefficient \(d_{33}\) can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit ferroelectric domain structures consistent with tetragonal micron-sized domains, as revealed by optical observation and Raman spectroscopy. The multidomain crystals have lower \(d_{33}\) values, 225 and 130 pC/N for [011] and [111]-oriented crystals, respectively. This trend is commented on from a domain-engineering perspective.     

Crystal and electronic structure study of AgPd3Se

The AgPd₃Se compound was synthesised from individual elements by solid-state chemical reactions and structurally characterized by powder X-ray diffraction data. AgPd₃Se displays cubic symmetry, space group Pa3?, unit cell parameter a=8.6289(1) Å and Z=8. Double-Friauf polyhedra (DFP), defined by Pd and Se atoms, form the basic structural building block of the AgPd₃Se crystal structure. The Ag atoms occupy the centres of DFPs forming an Ag–Ag dimer (2.792(2) Å). The packing of DFPs forms two kinds of interpenetrating networks that show similar features as three-dimensional Penrose tiles. AgPd₃Se is isostructural with CaAu₃Ga. The electric resistivity as well as the electronic structure calculation suggests metallic behaviour.