Gernot Zahn

Electronic Raman transitions from the vanadium(III) hexa-aqua cation, in guanidinium vanadium sulphate

Abstract Electronic Raman transitions ( 3 A → 3 E ( C 3 ) ) have been observed between the trigonally split components of the 3 T 1 g ( O h ) ground term of the vanadium(III) hexa-aqua cation in guanidinium vanadium sulphate hexa-hydrate. The magnitude of the trigonal field splitting is considerable, ∼2720 cm −1 , which is consistent with expectations based on the stereochemistry of the [V(OH 2 ) 6 ] 3+ complex. It is shown that a satisfactory reproduction of the electronic Raman band profile can be obtained only by assuming a ( 3 A ⊕ 3 E )⊗e vibronic coupling model.

Pressure dependence of unit cell geometry of single crystalline TbNi2B2C

Abstract The effect of hydrostatic pressure up to 5.56 GPa on the lattice parameters of TbNi 2 B 2 C has been studied at room temperature. Both lattice parameters and axial ratio c / a of the tetragonal unit cell are decreasing continuously with increasing pressure. The bulk modulus varies between 138 GPa and 196 GPa.

Structural studies with TbNi2B2C single crystals and TbxY(1−x)Ni2B2C polycrystals

Abstract X-ray powder diffraction has been used for structure refinement of Tb x Y (1− x ) Ni 2 B 2 C compounds of different compositions at room temperature. Lattice parameters, structure parameter z B and Tb content x were derived from Rietveld refinements. Lattice parameters a and c of the pseudoquaternary intermetallic compounds Tb x Y (1− x ) Ni 2 B 2 C show a linear behaviour and fulfil Vegards law. For the first time structure data obtained with single crystals are reported for TbNi 2 B 2 C as a function of temperature. Coefficients of linear thermal expansion vary between α a =0.6×10 −5 K −1 (90 K)–1.6×10 −5 K −1 (300 K) and α c =−1.1×10 −6 K −1 (90 K)–0.9×10 −6 K −1 (300 K) while the axial ratio c / a of the unit cell decreases with increasing temperature T .

Incommensurately modulated CeSi1.82

Abstract An incommensurately modulated structure of CeSi1.82 as determined by single-crystal X-ray diffraction at room temperature is reported. The observed satellite reflections reduce the orthorhombic symmetry of the X-ray pattern to a monoclinic one. This suggests the description of the modulated structure in the monoclinic superspace group I2/b(αβ0)00. The modulation wave vector was determined to q = 0.410(1) · a* + 0.610(1) · b*. The refinement was done using harmonic modulation functions for the displacement and the occupation probability of the atoms, the quality parameters converged to Robs = 3.33% (Robs = 2.56% for the main reflections, Robs = 8.88% for the 1st order satellite reflections and Robs = 33.06% for the 2nd order satellite reflections). The origin of the observed satellite reflections is attributed to a modulation of the partly occupied Si site caused by composition changes within the crystal.

Laue asterism and high temperature deformation of iron doped NiAl single crystal

Abstract Samples of iron doped NiAl single crystal were uniaxially compressed at temperatures up to 1673 K and a strain rate of 10 −3 s −1 , and were then studied with Laue back reflection method based on a STOE imaging plate diffraction system (IPDS). Asterism was observed for every deformed sample, which is an indication of orientation distribution and lattice distortion. A single Taylor axis can often, though not always be determined locally. However, different Taylor axes have been observed within a single sample, which could refer to multiple slip activated by plastic deformation. Possible slip systems can be deduced by studying Laue asterism combined with other measurements such as surface slip trace analysis. Furthermore, structure refinement has been carried out with the integrated intensity of distorted reflections.