[en] We discuss the use of self-seeding schemes with wake monochromators to produce TW power, fully coherent pulses for applications at the dedicated bio-imaging beamline at the European X-ray FEL, a concept for an upgrade of the facility beyond the baseline previously proposed by the authors. We exploit the asymmetric and symmetric Bragg and Laue reflections (sigma polarization) in diamond crystal. Optimization of the bio-imaging beamline is performed with extensive start-to-end simulations, which also take into account effects such as the spatio-temporal coupling caused by the wake monochromator. The spatial shift is maximal in the range for small Bragg angles. A geometry with Bragg angles close to π/2 would be a more advantageous option from this viewpoint, albeit with decrease of the spectral tunability. We show that it will be possible to cover the photon energy range from 3 keV to 13 keV by using four different planes of the same crystal with one rotational degree of freedom.

[en] Structural analysis of spin frustrated Ho₂Ge_xTi_2−xO₇ (x = 0, 0.1, 0.15 & 0.25) pyrochlore oxides has been performed using high resolution x-ray diffraction pattern and low temperature synchrotron x-ray diffraction pattern. The effect of positive chemical pressure on the spin dynamics of Ho₂Ge_xTi_2−xO₇ has been analysed through the study of static (M–T and M–H; magnetisation against temperature & magnetisation against magnetic field) and dynamical (ac susceptibility) magnetic measurements. In lower temperature regime (∼2 K), such systems are predominantly governed by competing exchange (J _nn) and dipolar (D _nn) magnetic interactions. Magnetic measurements indicate that the application of increased chemical pressure in Ho₂Ti₂O₇ matrix propels the system towards diminished ferromagnetic interaction. Dipolar coupling constant remains almost unchanged but Curie–Weiss temperature (θ _cw) reduces to −0.04 K from 0.33 K (for an applied magnetic field; H = 100 Oe) with increasing x in Ho₂Ge_xTi_2−xO₇. Positive chemical pressure establishes the dominance of Ho–Ho antiferromagnetic interaction J _nn over dipolar interaction D _nn. Spin relaxation feature corresponding to thermally activated single ion freezing (T _s∼15 K) is shifted towards lower temperature. This chemical pressure-driven T _s shift is ascribed to the alteration in crystal field effect, which reduces the activation energy for singe ion spin freezing. The reduction in the activation energy indicates crystal field-phonon coupling in Ho₂Ge_xTi_2−xO₇ system. The robustness in spin ice freezing (second spin relaxation feature in ac susceptibility curve) remains unaffected with increasingly chemical pressure. This spin freezing (‘2 in-2 out’ spin arrangement in tetrahedra) is related to quantum tunnelling phenomenon, at T _ice ∼ 2 K. It indicates that majority of spins still follows the ‘ice rule’ in Ho₂Ge_xTi_2−xO₇ even after the application of chemical pressure. (paper)

[en] High-pressure behaviours of isomorphous HoMn₂O₅ and BiMn₂O₅ (Pbam, Z = 4) were studied, using Raman spectroscopy and single-crystal x-ray diffraction, with the samples in diamond anvil cells pressurized to 10.09 GPa and 8.54 GPa, respectively, at room temperature. No phase transition was detected in either material. The two manganates are most compressible along the a axis with the lattice contractions along the b and c directions nearly the same. Their P-V data fitted with the second-order Birch-Murnaghan equation of state (B' = 4.0) give the bulk moduli B₀ = 138(2) GPa for BiMn₂O₅ and B₀ = 173(3) GPa for HoMn₂O₅. The difference in bulk moduli results from BiMn₂O₅ being more compressible than HoMn₂O₅ along the a axis. Our study shows that the Mn-O frameworks in isomorphous RMn₂O₅ compounds (R = Bi and rare earth) are not rigid at high pressures, but rather adapt to the behaviour of the coordination spheres around the R atoms. Bond valence calculations indicate that the pressure-induced charge transfers between the two Mn sites have different characters for the two compounds.

[en] The high-pressure behaviour of Bi₂Fe₄O₉ was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi₂Ga₄O₉. The lower phase transition pressure of Bi₂Fe₄O₉ with respect to that of Bi₂Ga₄O₉ (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga³⁺ and Fe³⁺ in tetrahedral coordination at high pressure. A fit of a second-order Birch-Murnaghan equation of state to the p-V data results in K₀ = 74(3) GPa for the low-pressure phase and K₀ = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements. (paper)

[en] Highlights: • The LiH–MgB_2 system was doped with TiCl_3 and milling conditions varied. • A heuristic model was used to estimate energy transfer from milling conditions. • Milling parameters were correlated with the energy transfer calculation. • 20 kJ g"−"1 of energy transfer correlates to the optimum conditions for the system. - Abstract: Hydrogen sorption properties of the LiH–MgB_2 system doped with TiCl_3 were investigated with respect to milling conditions (milling times, ball to powder (BTP) ratios, rotation velocities and degrees of filling) to form the reactive hydride composite (RHC) LiBH_4–MgH_2. A heuristic model was applied to approximate the energy transfer from the mill to the powders. These results were linked to experimentally obtained quantities such as crystallite size, specific surface area (SSA) and homogeneity of the samples, using X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method and scanning electron microscopy (SEM), respectively. The results show that at approximately 20 kJ g"−"1 there are no further benefits to the system with an increase in energy transfer. This optimum energy transfer value indicates that a plateau was reached for MgB_2 crystallite size therefore the there was also no improvement of reaction kinetics due to no change in crystallite size. Therefore, this study shows that an optimum energy transfer value was reached for the LiH–MgB_2 system doped with TiCl_3

[en] Different SrTiO${}_3$ thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO${}_3$ films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO${}_3$ films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe${}_{Sr}$ and Ti${}_{Sr}$) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably Ti${}_{Sr}^{\bullet <!--\; ???\; -->\bullet <!--\; ???\; -->}$) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping. (© 2022 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)