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The laser-diode-heated floating-zone (LDFZ) is a new variant of the floating-zone (FZ) technique where the molten-zone is established using a set of horizontal laser beams. Unlike a conventional mirror-type FZ, the non-divergent property of the laser beam in LDFZ allows for the growth of high melting temperature refractory materials comprising volatile components. The compound ErVO3 not only has a high melting temperature (∼2100 °C), it also contains volatile V2O3 as one of the components. We show here that large (cm-size) and high-quality crystals of ErVO3 can be obtained with relative ease using the LDFZ technique. In contrast, using the conventional FZ technique, an excessive evaporation of V2O3 from the molten-zone and the feed-rod led to discontinuation of growth within a short time; and the resulting boule, about 2 cm long, was essentially polycrystalline with tiny (less than 1 mm in size) crystals embedded in it. The high-quality of the LDFZ-grown crystal boule is inferred using optical and electron microscopies, Laue backscattering and neutron diffraction techniques. Magnetic susceptibility, neutron diffraction and specific heat measurements on the grown crystal confirmed the presence of orbital ordering at TOO = 195 K, V3+ spin ordering at TM1 = 110 K, simultaneous spin and orbital ordering at TM2 = 58 K, and the long-range ordering of the Er moments near 2.5 K. Our work establishes a relatively straightforward method of growing large crystals of the RVO3 family of compounds. The method can be extended to other high melting temperature refractory materials with volatile components.

This paper presents results from a numerical and experimental research programme motivated by the need to predict creep damage generated by multi-axial states of stress in austenitic stainless steels. It has been hypothesized that highly triaxial residual stress fields may be sufficient to promote creep damage in thermally aged components, even in the absence of in-service loads. Two prerequisites to test this hypothesis are the provision of test specimens containing a highly triaxial residual stress field and an accurate knowledge of how this residual stress field relaxes due to creep. Creep damage predictions may then be made for these specimens and compared to damage observed in experiments. This paper provides solutions to both of these prerequisites. Cylindrical and spherical test specimens made from type 316H stainless steel are heated to 850°C and then quenched in water. Finite element predictions of the residual stress state, validated by extensive neutron diffraction measurements, are presented which confirm the high level of triaxiality present in the specimens. The specimens are then thermally aged at 550°C and numerical predictions of the residual stress relaxation are given, again validated by extensive neutron diffraction measurements. The results confirm the validity of the creep relaxation models employed. In addition, the results show the influence of specimen size and permit comparisons to be made between three different types of neutron diffractometers.

POLDI (Pulse-OverLap DIffractometer) is a multiple pulse-overlap diffractometer at PSI, which is designed mainly for strain-scanning experiments. The multiple pulse-overlap method made it possible to build a time-of-flight diffractometer at a continuous neutron source with short flight path, high resolution and high intensity. The best achievable resolutions for the relative linewidths of the Bragg reflections are between 1×10−3 and 2×10−3, depending on the lattice spacing. The layout of the instrument and the features of the chopper, the neutron mirror and the 3He detector in time-focusing geometry are presented. The overall performance of the instrument is discussed with examples of strain-field measurements.

The concept of a novel type of time-of-flight diffractometer for continuous neutron sources is presented. The method is based on multiple overlapping neutron pulses and allows a tuning of the instrument to high intensity and high resolution simultaneously. The dependence of the time of flight of the neutrons on the scattering angle in combination with the different intervals between successive neutron pulses are used as extra parameters for the analysis of the frame-overlap data. The instrument concept is most suitable for strain-scanning applications where high resolution in lattice spacing is necessary although the total number of Bragg reflections is quite low.

The interstitial D sites in the D-doped A-15 compound Ti3IrDx with x = 0.70 and 3.63 were determined by neutron diffraction (space group Pm 3 n (No. 223)). For x = 0.70, we confirm the D occupation of sixfold d positions (6d positions) already found for other H- and D-doped A-15 compounds. The complete and sole occupation of these positions yields the concentration x = 3. Accordingly, we found for the sample with x = 3.63 the additional occupation of 24k (or nearly 24k) positions. Our study suggests in particular a structural mechanism that successively replaces 6d positions by two adjacent and simultaneously occupied 24k positions in order to allow an increase of the D concentration above x = 3.

Concentration fluctuations of impurity atoms in solids, such as hydrogen in metals, are accompanied by coherency stresses if the impurity atoms expand or contract the lattice. The coherency stresses raise the elastic energy which accelerates the diffusive decay of the fluctuations and increases, therefore, the value of a diffusion coefficient defined according to Fick’s law. We studied the influence of coherency stresses on deuterium diffusion in NbD 0.33 by neutron spectroscopy, separating coherent and incoherent scattering by neutron spin analysis. The diffusion coefficient D bulk of the deuterium interstitials, obtained from the coherent scattering intensity, was found up to 30 times larger than the diffusion coefficient D chem reported from Gorsky effect measurements [H.C. Bauer, J. Volkl, T. Tretkowski, G. Alefeld, Z. Physik B29 (1978) 17] on the same system, in spite of the fact that both diffusion coefficients describe deuterium diffusion according to Fick’s law. We demonstrate that the large differences between D bulk and D chem reflect a dissimilar influence of coherency stresses on these two quantities, and that the differences can quantitatively be described within the elasticity-theoretical concept of Wagner and Horner.

Magnons and phonons in Ni2MnGa were investigated with neutron spectroscopy. The alloy shows a martensitic phase transition from a cubic high-temperature phase to a tetragonal one within the ferromagnetic state, about 80 K below the Curie temperature. The spin waves show no anisotropy in the low-energy range. The corresponding magnetic exchange stiffness constant is 108 ± 10 meV A 2 . The TA2-phonon branch shows a strong but incomplete softening at ξ ∼ 1 3 when the temperature approaches the martensitic phase transition temperature.