Hermann Franz

Performance of a picosecond x-ray delay line unit at 8.39 keV

A prototype device capable of splitting an x-ray pulse into two adjustable fractions, delaying one of them with the aim to perform x-ray photon correlation spectroscopy and pump-probe type studies, was designed, manufactured, and tested. The device utilizes eight perfect silicon crystals in vertical 90 degrees scattering geometry. Its performance has been verified with 8.39 keV synchrotron radiation. The measured throughput of the device with a Si(333) premonochromator at 8.39 keV under ambient conditions is 0.6%. Time delays up to 2.62 ns have been achieved, detected with a time resolution of 16.7 ps.

Development of a hard X-ray delay line for X-ray photon correlation spectroscopy and jitter-free pump–probe experiments at X-ray free-electron laser sources

A prototype device capable of splitting an X-ray pulse into two adjustable fractions, delaying one of them with the aim of performing split pulse X-ray photon correlation spectroscopy and pump–probe type studies was designed and manufactured. Time delays up to 2.95 ns have been demonstrated. The achieved contrast values of 56% indicate a feasibility of performing coherence-based experiments with the delay line.

Atomic structure of Al88Y7Fe5 metallic glass

The structure of Al88Y7Fe5 metallic glass has been investigated by differential scanning calorimetry, x-ray powder diffraction, and x-ray absorption fine structure (XAFS) techniques. The amorphous alloy crystallizes according to the following scheme: amorphous→α‐Al+residual amorphous→α‐Al+Al3Y+AlFeY. The atomic structure of the amorphous alloy was modeled by reverse Monte Carlo methods. The resulting structure indicates that the prepeak (at 1.42A−1) in the static structure factor S(Q) is caused by contributions of distinct Y-Y, Y-Fe pairs. From the analysis of our XAFS spectra at the Fe and Y K edge the following characteristics of the local structure are found: The interatomic distance between Fe and coordinated Al atoms in the amorphous state is significantly (8.9%) shorter than the sum of the nominal metallic-state radii. The average coordination number is anomalously 36% reduced compared to the value derived from the dense-random-packing (DRP) model, using again the nominal metallic-state radii. On th...

Strain distribution in Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass investigated by in situ tensile tests under synchrotron radiation

We report on the evolution of the atomic-scale strain tensor of ductile Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass under tensile loading by using x-ray synchrotron radiation. The same kind of samples was previously investigated under compressive loading and revealed yielding at 1690 MPa together with large deformability of up to 160% strain. In tension the samples fracture at a lower stress, 1500 MPa, with no sign of yielding or plastic deformation. With no macroplasticity observed under tension, large differences in the elastic constants obtained from the strain tensor and from ultrasonic sound velocity measurements are revealed. This paper presents in detail the measuring procedure as well as the calculation of the tensile tensor and pair distribution functions of Zr64.13Cu15.75Ni10.12Al10 at different stages of deformation. The results are discussed in comparison with other reported data obtained from x-ray diffraction measurements using synchrotron radiation.

Atomic structure and glass forming ability of Cu46Zr46Al8 bulk metallic glass

By using a combination of state-of-the-art experimental and computational methods, the high glass forming ability (GFA) of Cu46Zr46Al8 alloy is studied from the view of its atomic packing. Three-dimensional atomic configuration is well established. It is found that Al atoms almost homogeneously distribute around Cu and Zr atoms without segregation, causing the local environment around Cu and Zr atoms in Cu46Zr46Al8 bulk metallic glass different from that of the major competing phase of Cu10Zr7. Furthermore, the addition of Al not only increases the amount of icosahedronlike clusters but also makes them more homogeneous distribution, which can enhance the GFA by increasing the structural incompatibility with the competing crystalline phases.

Origin of nondetectable x-ray diffraction peaks in nanocomposite CuTiZr alloys

Microscopic structures of Cu60Ti10+xZr30−x (x=0 and 10) alloys have been investigated by transmission electron microscopy, x-ray diffraction (XRD) and differential scanning calorimeter (DSC). In the Cu60Ti10Zr30 samples annealed at 708 K for times ranging from 0 to 130 min, where the enthalpy of the first exothermic peak decreases by 80%, the corresponding XRD patterns still look similar to that for the as-prepared sample. However, the simulated XRD patterns for the pure Cu51Zr14 phase, which is the crystalline phase formed during the first exothermic reaction, with small grain sizes and defects clearly show a broadened amorphous-like feature. This might be the reason that no diffraction peaks from the nanocrystalline component were detected in the XRD patterns recorded for the as-cast or as-spun Cu60Ti10+xZr30−x (x=0 and 10) alloys and for the alloys annealed at lower temperatures, in which the enthalpy of the first exothermic peak has a significant reduction. The second exothermic peak found in DSC curv...

Crystallization of Cu60Ti20Zr20 metallic glass with and without pressure

Structural stability of a Cu 6 0 Ti 2 0 Zr 2 0 metallic glass under pressure up to 4.5 GPa was investigated by x-ray diffraction. The sample exhibited a supercooled liquid region of 33 K and a ratio of the glass-transition temperature to the liquidus temperature of 0.63. The glass crystallized in two-step transformation processes in the pressure range of 0-4.5 GPa; the first was a primary reaction to form a Cu 5 1 Zr 1 4 -type structure crystalline phase with a spacing group P6/m (175) and lattice parameters a = 11.235 A and c = 8.271 A, and then the residual amorphous phase crystallized into a MgZn 2 -type structure crystalline phase with a spacing group P6 3 /mmc (194) and lattice parameters a = 5.105 A and c = 8.231 A. Both crystallization temperatures increased with pressure having a slope of 19 K/GPa. The increase of the first crystallization temperature with increasing pressure in the glass can be explained by the suppression of atomic mobility. No significant structural change was detected in the Cu 6 0 T1 2 0 Zr 2 0 glass annealed in vacuum at 697 K for 1 h as compared to the as-prepared sample from x-ray diffraction measurements.

Beamline P02.1 at PETRA III for high‐resolution and high‐energy powder diffraction

By providing the capabilities for high-resolution, high-energy and time-resolved powder X-ray diffraction, beamline P02.1 is a versatile tool to tackle various problems in materials science, crystallography and chemistry.

Atomic structure in Zr70Ni30 metallic glass

Atomic structure of Zr70Ni30 metallic glass (MG) was investigated by reverse Monte Carlo simulation combining with x-ray diffraction and Ni and Zr K-edge extended x-ray absorption of fine structure measurements. Distributions of coordination number (CN) and Voronoi clusters were analyzed by Voronoi tessellation method. The average CN of atoms was obtained to be 11.4 together with the average CN of Zr and Ni atoms of about 11.8 and 10.6, respectively. It is found that Z11 Kasper polyhedron and distorted icosahedra are mainly favored structural units in Zr70Ni30 MG. The discrepancy in atomic structure between Zr70Ni30 MG and its corresponding crystalline (or quasicrystalline) phases can explain the fact that Zr70Ni30 MG does not transform to neither icosahedral nor fcc Zr2Ni phase during crystallization process.

The Extreme Conditions Beamline P02.2 and the Extreme Conditions Science Infrastructure at PETRA III

Performance description of the Extreme Conditions Beamline (ECB, P02.2) at PETRA III that is optimized for micro-diffraction at simultaneous high pressure and high and low temperatures created in different diamond anvil cells environments. Additional information of the capabilities of the Extreme Conditions Science Infrastructure for DAC work is provided.