Inelastic X-ray Scattering Measurements Research Articles

LO-mode phonon of KCl and NaCl at 300 K by inelastic x-ray scattering measurements and first principles calculations

Longitudinal-optical (LO) mode phonon branches of KCl and NaCl were measured using inelastic x-ray scattering (IXS) at 300 K and calculated by the first-principles phonon calculation with the stochastic self-consistent harmonic approximation. Spectral shapes of the IXS measurements and calculated spectral functions agreed well. We analyzed the calculated spectral functions that provide higher resolutions of the spectra than the IXS measurements. Due to strong anharmonicity, the spectral functions of these phonon branches have several peaks and the LO modes along Γ–L paths are disconnected.

Phonon excitations in a single crystal Mg85Zn6Y9 with a synchronized long-period stacking ordered phase

Inelastic X-ray scattering (IXS) experiments were carried out at room temperature at BL35XU of the SPring-8 on a single crystal Mg85Zn6Y9 alloy with a synchronized long-period stacking ordered (LPSO) phase of purely 18R type. The IXS measurements were carried out in both the longitudinal and transverse directions along the Γ-K and Γ-M (momentum vector q⊥ lattice axis c), and Γ-A (q∥c) directions for the energy transfers ω below 40 meV. Peaks arising from longitudinal and transverse acoustic (LA and TA) modes were clearly observed in the IXS spectra. The dispersion relations of the LA and TA modes in the Mg85Zn6Y9 LPSO alloy are mostly similar to those of previous INS data on single crystal pure Mg. New impurity-derived dispersion-less excitation modes are observed along all of the crystal directions at about 5, 10, and 17 meV. Partial vibrational density of states (vDOS) was obtained using an abinitio molecular dynamics simulation, and it was found that the ∼10 meV peak mainly originates from the phonon excitations inside the L12-type Zn6Y8 clusters and the ∼17 meV peak from those between the cluster and the host Mg atoms, and a small shoulder at 5 meV consists of motions of all the elements. These findings clarify that the dispersion-less modes mainly correspond to localized stretching and twisting modes around the impurity clusters in the LPSO alloys.

Inelastic X-ray scattering of RTAl3 (R = La, Ce, T = Cu, Au)

Inelastic X-ray scattering (IXS) experiments of RTAl3 (R = La Ce, T = Cu, Au) were carried out at 300 and 5.5K. The spectra between LaCuAl3 and CeCuAl3 (LaAuAl3 and CeAuAl3) are nearly identical at both temperatures except for temperature factors such as temperature dependence of Bose factor in IXS spectra and effect on thermal expansion. This means that no evident temperature dependence of IXS spectra was observed in CeTAl3 (T = Cu, Au). Since the major contribution of scattering cross section in IXS measurements is Thomson scattering, the present results failed to confirm the presence of vibron in these compounds.

Impurity effects in the microscopic elastic properties of polycrystalline Mg-Zn-Y alloys with a synchronized long-period stacking ordered phase

Inelastic X-ray scattering (IXS) experiments were performed on polycrystalline Mg97Zn1Y2 and Mg85Zn6Y9 alloys with synchronized long-period stacking ordered (LPSO) phase of about 24% and 100%, respectively, together with the reference pure Mg at room temperature for investigating the impurity effects in the microscopic elastic properties of the LPSO alloys. Inelastic neutron scattering (INS) measurements were also carried out on a polycrystalline Mg97Zn1Y2 alloy. The IXS measurements were carried out for the momentum transfers Q between 1.6 and 15.9 nm−1 including the whole first- and partially second Brillouin zones, and for the energy transfers ω below 40 meV. Peaks arising from longitudinal acoustic (LA) modes were clearly observed in the IXS spectra of both the LPSO alloys and pure Mg, while transverse acoustic (TA) modes can mainly be detected in the second Brillouin zone. The dispersion relations in pure polycrystalline Mg are in good agreement with those of previous INS data on single crystal Mg. Broader inelastic signals and larger quasielastic peaks are characteristic for the LPSO alloys due to the phonon scattering by the Zn/Y impurities. Only the TA excitation energies increase by adding the impurities, which indicate a harder stiffness of the bond angles relating to the existence of the L12-type clusters in the LPSO alloys. Besides, new impurity-derived dispersion-less excitation modes are observed at about 10 meV by adding the Zn/Y impurities. By comparing with the INS data on the polycrystalline LPSO alloy, the contributions of the impurities to these excitation modes are discussed using the differences in the scattering cross-sections between neutrons and X-rays.

Low-energy optical phonon modes in the caged compoundLaRu2Zn20

The caged compound LaRu2Zn20 exhibits a structural transition at TS =150 K, whose driving mechanism remains elusive. We have investigated atomic dynamics by the measurements of specific heat C and inelastic X-ray scattering (IXS). The lattice part of the specific heat Clat divided by T3, Clat/T3, shows a broad peak at around 15 K, which is reproduced by two Einstein modes with characteristic temperatures of 35 K and 82 K, respectively. IXS measurements along the [111] and [110] directions reveal optical phonon modes at 3 meV (35 K) and 7 meV (80 K), respectively, whose values agree with the values of Einstein temperatures. The first principles calculation has assigned the phonon modes at 3 meV as the optical modes of Zn atoms located at the middle of two La atoms. The low-energy vibration of the Zn atom perpendicular to the there-fold axis is thought to lead the structural instability of LaRu2Zn20.

Temperature dependence of the velocity-density relation for liquid metals under high pressure: Implications for the Earth’s outer core

The relationship between the sound velocity, density, and temperature of liquid metals is important when one tries to interpret the seismic velocity profile and infer the chemical compositions of the Earth’s outer core. We, therefore, have experimentally measured the longitudinal acoustic (LA) velocity of liquid indium under high P-T conditions. Also, we examined a Hugoniot data of liquid iron by comparing with an existing equation of state (EoS). The LA velocities of liquid and solid indium at pressures up to 6.7 GPa and temperatures mostly at 710 K were measured using inelastic X-ray scattering (IXS) to probe samples in an externally heated diamond-anvil cell. A thermal EoS for liquid indium derived from existing literature was used to calculate the density for the IXS measurements and to provide an independent check on the sound velocities. The IXS data are consistent with the hydrodynamic LA velocity derived from the liquid EoS, implying that the positive dispersion is minimal in liquid indium. The velocity-density relation for liquid indium derived from the EoS has temperature dependence, implying that Birch’s law does not hold for the liquid phase. Similarly we calculated the temperature-velocity-density relation of liquid iron over the Earth’s core range from a recently reported EoS. The resulting velocity-density relation is also temperature dependent, indicating that liquid iron thus does not follow Birch’s law. The violation of Birch’s law implies that the Hugoniot data cannot be directly compared with seismological observations because of the different temperature ranges. Formulation of the temperature-velocity-density of liquid iron-alloys supported by experimental measurements provides better understanding of the thermodynamic state of the Earth’s core.

Communication: Collective dynamics of room-temperature ionic liquids and their Li ion solutions studied by high-resolution inelastic X-ray scattering

High-resolution inelastic X-ray scattering (IXS) measurements were performed for room-temperature ionic liquids (ILs) of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide, [C2mIm(+)][TFSA(-)] and [C2mIm(+)][FSA(-)], respectively, at ambient temperature. The observed spectra as a function of Q of 1.4-6 nm(-1) can be ascribed to quasi-elastic and inelastic scatterings, so that they are well represented with the fitting by using the Lorentz and the damped harmonic oscillator model functions to yield the dynamic structure factors. It was found in the intermediate scattering function, F(Q, t) that both ILs show the relaxation at t < 10 ps. The IXS measurements were also made on [C2mIm(+)][TFSA(-)] and [C2mIm(+)][FSA(-)] solutions dissolving Li salt. It is suggested that the adding of Li salt to IL significantly prolongs the relaxation time.

Hydration structures near finite-sized nanoscopic objects reconstructed using inelastic x-rayscattering measurements

Recent work has shown that it is possible to use high resolution dynamical structure factorS(q,ω) data measured with inelastic x-ray scattering to reconstruct the Green’s function ofwater, which describes its dynamical density response to a point charge. Here, wegeneralize this approach and describe a strategy for reconstructing hydrationbehavior near simple charge distributions with excluded volumes, with the longterm goal of engaging hydration processes in complex molecular systems. We usethis Green’s function based imaging of dynamics method to generate hydrationstructures and show that they are consistent with those of well-studied model systems.

Ｘ線非弾性散乱の新展開

Advances in synchrotron radiation sources have opened up a new frontier of inelastic X-ray scattering (IXS) spectroscopy. The IXS measurements with a resolution much better than a few eV are now becoming feasible. Such experiments can be used to study various properties of condensed systems: e.g., electron correlations in the ground state (Compton-Raman scattering), eV and sub-eV electronic excitations (X-ray Raman scattering and small-angle IXS), and meV phonon excitations (ultra-high resolution IXS) .

Inelastic X-Ray Scattering Measurements at BM29

An inelastic x-ray scattering spectrometer has been implemented on the bending magnet beamline BM29 at the ESRF. It comprises a spherically bent perfect crystal as a Bragg analyser in near back reflection and a linear position sensitive detector (PSD) in Rowland's geometry. The setup exploits the wide horizontal radiation fan from a dipole magnet to create an extended source so that several eV of scattered radiation are simultaneously imaged onto the PSD with a static analyser crystal. This is in contrast to existing configurations using undulator or wiggler sources where one component of the emission spectrum is imaged and the analyser has to be scanned in angle. Results are shown at the holmium L III edge where the resolution is better than ∼0.3 eV throughout the whole spectrum.