I. Sergueev

Lattice dynamics in the FeSb3 skutterudite

Thin films of FeSb{sub 3} were characterized by electronic transport, magnetometry, x-ray diffraction, {sup 57}Fe and {sup 121}Sb nuclear inelastic scattering, and {sup 57}Fe Moessbauer spectroscopy. Resistivity and magnetometry measurements reveal semiconducting behavior with a 16.3(4) meV band gap and an effective paramagnetic moment of 0.57(6) {mu}B, respectively. A systematic comparison of the lattice dynamics with CoSb{sub 3} and EuFe{sub 4}Sb{sub 12} reveals that the Fe{sub 4}Sb{sub 12} framework is softer than the Co{sub 4}Sb{sub 12} framework, and that the observed softening and the associated lowering of the lattice thermal conductivity in the RFe{sub 4}Sb{sub 12} filled skutterudites are not only related to the filler but also to the Fe{sub 4}Sb{sub 12} framework.

Lattice instabilities in bulk EuTiO3

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using X-ray and neutron diffraction, 151-Eu-Mossbauer spectroscopy, and 151-Eu nuclear inelastic scattering, and macroscopically using calorimetry, resonant ultrasound spectroscopy, and magnetometry. Furthermore, our investigations were corroborated by ab initio theoretical studies. The perovskite symmetry, Pm-3m, is unstable at the M- and R- points of the Brillouin zone. The lattice instabilities are lifted when the structure relaxes in one of the symmetries: I4/mcm, Imma, R-3c with relative relaxation energy around -25 meV. Intimate phase analysis confirmed phase purity of our ceramics. A prominent peak in the Eu specific density of phonon states at 11.5 meV can be modelled in all candidate symmetries. A stiffening on heating around room temperature is indicative of a phase transition similar to the one observed in SrTiO3, however, although previous studies reported the structural phase transition to tetragonal I4/mcm phase our detailed sample purity analysis and thorough structural studies using complementary techniques did not confirm a direct phase transition. Instead, in the same temperature range, Eu delocalization is observed which might explain the lattice dynamical instabilities.

129Xe nuclear resonance scattering on solid Xe and 129Xe clathrate hydrate

Nuclear inelastic and nuclear forward-scattering experiments utilizing the 129Xe M?ssbauer resonance were performed on solid Xe and enriched 129Xe clathrate hydrate. The lifetime and energy of the nuclear resonance were determined to be and , respectively. Nuclear inelastic scattering spectra could be obtained with an instrumental resolution of . Despite low Lamb-M?ssbauer factors, Xe specific densities of phonon states were derived for solid Xe and Xe clathrate hydrate. Their reliability was investigated using 1-phonon terms obtained by fixing Lamb-M?ssbauer factor values within the applied Fourier-Log decomposition. ABINIT calculations of the density of phonon states in solid Xe supplement the interpretation of the experimental data for fcc Xe and good agreement with published densities of phonon states could be achieved below . Results for the Xe clathrate hydrate essentially confirm the rattling nature of the Xe guests and indicate that Xe modes do not contribute to lattice dynamics above .

Spin disorder in maghemite nanoparticles investigated using polarized neutrons and nuclear resonant scattering

The manuscript reports the investigation of spin disorder in maghemite nanoparticles of different shape by a combination of polarized small-angle neutron scattering (SANSPOL) and nuclear forward scattering (NFS) techniques. Both methods are sensitive to magnetization on the nanoscale. SANSPOL allows for investigation of the particle morphology and spatial magnetization distribution and NFS extends this nanoscale information to the atomic scale, namely the orientation of the hyperfine field experienced by the iron nuclei. The studied nanospheres and nanocubes with diameters of 7.4 nm and 10.6 nm, respectively, exhibit a significant spin disorder. This effect leads to a reduction of the magnetization to 44% and 58% of the theoretical maghemite bulk value, observed consistently by both techniques.

121Sb and125Te nuclear inelastic scattering in Sb2Te3under high pressure

We investigated the lattice dynamics of Sb2Te3 under high pressure using 121Sb and 125Te nuclear inelastic scattering of synchrotron radiation. We measured the room temperature 121Sb and 125Te inelastic spectra at 15(1) GPa and 77(3) GPa and extracted the Te and Sb element specific density of phonon states of δ-Sb2Te3 at 77(3) GPa. X-ray diffraction confirms the sample to be in the cubic δ-Sb2Te3 phase with space group and lattice constant . The total density of phonon states of δ-Sb2Te3 strongly resembles the one of amorphous GeSb2Te4, suggesting the presence of covalent bonding in contrast to the resonance bonding in α-Sb2Te3. From the density of phonon states of δ-Sb2Te3 a mean speed of sound of 2.61(6) and Debye temperatures of 278(10) K for Te and 296(10) K for Sb were determined.

Nuclear forward scattering by the 68.7 keV state of 73Ge in CaGeO3 and GeO2

We measured nuclear forward scattering of synchrotron radiation by the 68.7 keV nuclear resonance of 73Ge with a half-life . The Debye temperatures of CaGeO3 in the wollastonite, garnet and perovskite phases were determined to be 386(20) K, 437(20) K and 507(20) K, respectively, and 309(20) K and 459(11) K for GeO2 in the quartz and rutile phases, respectively. The isomer shift is clearly dependent on the Ge valence but not directly on the coordination geometry. The so far unknown magnetic moment μe of the 68.7 keV excited state of 73Ge is determined to be . Time domain 73Ge Mossbauer spectroscopy with the 68.7 keV resonance is feasible for isomer shift and Debye temperature measurements but so far neither electric quadrupole nor magnetic hyperfine interactions could be observed.

Rocking curve imaging of high quality sapphire crystals in backscattering geometry

We report on the characterization of high quality sapphire single crystals suitable for high-resolution X-ray optics at high energy. Investigations using rocking curve imaging reveal the crystals to be of uniformly good quality at the level of ∼10−4 in lattice parameter variations, δd/d. However, investigations using backscattering rocking curve imaging with a lattice spacing resolution of δd/d∼5×10−8 show very diverse quality maps for all crystals. Our results highlight nearly ideal areas with an edge length of 0.2–0.5u2009mm in most crystals, but a comparison of the back reflection peak positions shows that even neighboring ideal areas exhibit a relative difference in the lattice parameters on the order of δd/d=10– 20×10−8; this is several times larger than the rocking curve width. Stress-strain analysis suggests that an extremely stringent limit on the strain at a level of ∼100u2009kPa in the growth process is required in order to produce crystals with large areas of the quality required for X-ray optics at hi...

Lattice dynamics in the FeSb[subscript 3] skutterudite

Thin films of FeSb{sub 3} were characterized by electronic transport, magnetometry, x-ray diffraction, {sup 57}Fe and {sup 121}Sb nuclear inelastic scattering, and {sup 57}Fe Moessbauer spectroscopy. Resistivity and magnetometry measurements reveal semiconducting behavior with a 16.3(4) meV band gap and an effective paramagnetic moment of 0.57(6) {mu}B, respectively. A systematic comparison of the lattice dynamics with CoSb{sub 3} and EuFe{sub 4}Sb{sub 12} reveals that the Fe{sub 4}Sb{sub 12} framework is softer than the Co{sub 4}Sb{sub 12} framework, and that the observed softening and the associated lowering of the lattice thermal conductivity in the RFe{sub 4}Sb{sub 12} filled skutterudites are not only related to the filler but also to the Fe{sub 4}Sb{sub 12} framework.

Lattice dynamics in the FeSb3skutterudite

Thin films of FeSb{sub 3} were characterized by electronic transport, magnetometry, x-ray diffraction, {sup 57}Fe and {sup 121}Sb nuclear inelastic scattering, and {sup 57}Fe Moessbauer spectroscopy. Resistivity and magnetometry measurements reveal semiconducting behavior with a 16.3(4) meV band gap and an effective paramagnetic moment of 0.57(6) {mu}B, respectively. A systematic comparison of the lattice dynamics with CoSb{sub 3} and EuFe{sub 4}Sb{sub 12} reveals that the Fe{sub 4}Sb{sub 12} framework is softer than the Co{sub 4}Sb{sub 12} framework, and that the observed softening and the associated lowering of the lattice thermal conductivity in the RFe{sub 4}Sb{sub 12} filled skutterudites are not only related to the filler but also to the Fe{sub 4}Sb{sub 12} framework.