[en] The first part gives a brief overview about the employed methods (plane-wave basis, pseudopotentials, conjugated gradient methods, Verlet algorithm,...) The second part describes the application of this method on various systems: Trigonal and liquid tellurium, the stable crystalline compounds K2Te, K2Te2 and K2Te3 and the liquid compounds K2Te and KTe of the potassium-tellurium system. In addition the crystalline alloys K3Sb, K5Sb4 and KSb and the liquids K3Sb and KSb have been investigated. Special interest have been given to the preservation of structural and electronic properties of the crystalline compounds upon melting. (author)

[en] Nondestructive testing as an essential part for the inspection of high loaded products. Determinations in standards and specifications. Requirements to personnel and equipment. Examples for the development of modern, efficient automatic installations. New procedures and systems. (orig.)

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[en] ¹⁸¹Hf and ¹¹¹In ions were implanted into AlN-layers in order to investigate their immediate lattice site environment and its temperature dependence by means of the Perturbed Angular Correlation (PAC) technique. After rapid thermal annealing at 1273 K up to 50% of the probe atoms were incorporated on undisturbed lattice sites defined by an electric field gradient (EFG) of 33 MHz for In and 572 MHz for Hf for measurement at room temperature. PAC-spectra taken at temperatures between 25 and 1200 K show that the EFG measured at the site of the undisturbed probes changes with temperature. While for Hf it decreases by 3%, for In it increases by 25% within the measured temperature range. Thus, the change cannot be due only to the thermal lattice expansion. In the case of In the fraction of probe atoms on substitutional sites increases with temperature until it reaches nearly 100% at 973 K. These effects are fully reversible. For the Hf probe, an additional EFG was detected at temperatures above 300 K.

[en] Thulium ions were implanted into metal organic chemical vapour deposition (MOCVD) grown GaN films with different fluences at implantation temperatures of 20, 400 and 500 deg. C. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. The lattice damage introduced by the implantation and the effect of post-implant annealing were investigated with the Rutherford backscattering (RBS)/channelling technique. We observe that implantation at 500 deg. C considerably reduces the induced lattice damage and increases the amorphisation threshold. The lattice-site location of the implanted ions was determined by performing detailed channelling measurements for the <0 0 0 1> and <1 0 1-bar1> crystal directions. The results show that Tm ions mainly occupy substitutional Ga-sites directly after implantation and after annealing. The optical properties of the ion-implanted GaN films have been studied by room temperature cathodoluminescence (CL) measurements. Well-defined emission due to intra-4f shell transitions of the Tm³⁺ ions are observed in the blue spectral range at 477 nm and in the near infra-red (IR) at 804 nm

[en] Wide band-gap semiconductors, particularly III-nitrides, became one of the most studied materials during the last decades. These compounds are the base of a new generation of optoelectronic devices operating in the UV-Blue region of the electromagnetic spectrum. Incorporation of rare-earth (RE) ions into nitrides creates new routes to build all-nitride electroluminescent devices, using the sharp intra-4fⁿ transitions of these elements. The introduction of the RE ions in the nitride lattice during the growth or by ion implantation creates defects which influence the optical behaviour of the doped region. In this work we report the results on Yb implanted GaN. A combination of techniques (Rutherford backscattering/Channeling and Photoluminescence) was used to assess the mechanisms responsible for the optical and structural behaviour of the doped materials. Lattice site location experiments showed that Yb is incorporated into positions slightly displaced from the Ga-site. Clearly the optical activity of the RE could be enhanced by orders of magnitude reducing the number of non-radiative recombination paths related with defects.

[en] This paper reviews the current knowledge on rare earths (REs) implanted into GaN with a special focus on their lattice location and on the optical activation by means of thermal annealing. While emission channeling experiments have given information on the lattice location of rare earths following low-dose (∼10¹³ cm^-2) implantation, both in the as-implanted state and after annealing up to 900 deg. C, the lattice location of higher-dose implants (10¹⁴-10¹⁵ cm^-2) and their defect annealing behaviour were studied using the Rutherford backscattering/channeling (RBS/C) method. The available channeling and luminescence results suggest that the optical activation of implanted REs in GaN is related to their incorporation in substitutional Ga sites combined with the effective removal of the implantation damage

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[en] The design and construction of heat exchangers, especially in reactor engineering, with metal melts such as sodium or sodium/potassium used as a heat transfer medium brings up the problem of carbon transport between various materials through this medium. If the conventional ferritic and austenitic chrome -nickel steels are used side by side, carburization of the austenitic steels will take place whereby structural elements, such as the fuel element and moderator jackets, are adversely affected. This phenomenon is due to different activities of the carbon contained in the ferrite and austenite, and it is sufficiently known from the use of welded joints of the ferritic-austenitic type. It was therefore necessary to determine whether a suitable ferritic material with an adequately low carbon activity could be developed for sodium circuits. Compared with austenite, such a material has the advantage of a higher rate of economy, a fact to be taken into account along with the low material costs and also with its higher thermal conductivity and lower thermal expansion. Proceeding from the heat-resistant 2 1/4 chrome and 1% molybdenum steel, the effect of carbideforming elements upon the decarburization tendency when brought into contact with chrome -nickel austenite was studied at temperatures up to 700°C. Additions of niobium and titanium prevent decarburization, if the concentration is sufficient to stabilize the entire carbon and nitrogen. Diffusion tests showed that this condition is satisfied if the titanium or niobium content corresponds to the stoichiometrical composition of the respective carbides and nitrides. It was surprising to find that the carbide-forming element, vanadium, even at very high concentrations, did not effectively prevent carbon diffusion. Subsequently, preference was given to the Nb-stabilized material because niobium is much more suitable than titanium to obtain a sufficiently high stress -rupture strength. Because of the association of carbon with niobium and of the ferrite-forming effect of the latter element, it was expected that the properties of the conventional chrome-molybdenum steel would be altered. Examinations were therefore made to determine the influence of rising niobium contents on the transformation and precipitation properties. First, a quasi-binary section of the ironcarbon- chromium-.molybdenum-niobium system was established. This quasi-binary section, which by itself does not allow any conclusions to be drawn regarding the time-dependence of the transformation processes, was supplemented by a continuous TTT -diagram that helped to investigate fully the heat treatment characteristics of various cross -sections. Next, detailed examinations were carried out to determine the influence of niobium concentration on the technological properties. A close relationship was found to exist between the precipitation of Nb-carbide or iron-niobide and, in particular, the impact properties and yield strength. As the niobium acts unfavourably upon impact properties of this type of steel, limitation of the Nb -content and additions of suitable alloying elements, such as manganese or nickel, are necessary to ensure a sufficient degree of resistance to brittle fracture. Having due regard to all these factors, a ferritic material was produced with a sufficiently low carbon activity to meet the requirements of sodium-cooled reactors, as has been borne out by the processing of commercial melts into tubes, sheet metal and forgings. The properties essential for the manufacture and application of this steel are indicated, such as notched-bar impact strength, yield point at elevated temperature, stress-rupture strength and scaling properties in air and steam, as well as weldability when using electrodes made of a material identical with the parent metal. (author)