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| Home > Publications database > Nuclear Resonance Scattering Study of Iridates, Iridium and Antimony Based Pyrochlores |
| Book/Dissertation / PhD Thesis | PUBDB-2017-01621 |
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2017
Verlag Deutsches Elektronen-Synchrotron
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Please use a persistent id in citations: urn:nbn:de:gbv:18-84687 doi:10.3204/PUBDB-2017-01621
Report No.: DESY-THESIS-2017-013
Abstract: This thesis shows the first synchrotron-based Mössbauer spectroscopy studies on iridium containing compounds and first vibrational spectroscopy on Sb containing compounds carried out at the P01 beamline of PETRA III. In this context, two types of x-ray monochromators have been developed: a monochromator for 73 keV photons with medium energy resolution, and a high-resolution backscattering monochromator based on a sapphire crystal. The monochromator for 73 keV x-rays is the key instrument for hyperfine spectroscopy on Iridium compounds, while the sapphire backscattering monochromator is purposed to vibrational spectroscopy on any Mössbauer resonances with the transition energies in the 20-50 keV range. Additionally, the signal detection for nuclear resonance scattering experiments at the beamline was significantly improved during this work, inspired by the high energies and low lifetimes of the employed resonances. The first synchrotron-based hyperfine spectroscopy on Iridium-containing compounds was demonstrated by NRS on 73 keV resonance in $^{193}$Ir. The results can be interpreted by dynamical theory of nuclear resonance scattering. In this work, special emphasis is set onto the electronic and magnetic properties of Ir nuclei in IrO$_2$ and in Ruddlesden-Popper (RP) phases of strontium iridates Sr$_{n+1}$IrnO$_{3n+1}$ (n = 0; 1). These systems are well-suited for studies with x-ray scattering techniques, since the scattered signal contains vast information about the widely tunable crystallographic and electronic structure of these systems; furthermore, studies with x-rays are less limited by absorption from iridium as it is the case for neutron scattering experiments. The hyperfine parameters in IrO$_2$, SrIrO$_3$ and Sr$_2$IrO$_4$ have been measured via Nuclear Forward Scattering for the first time. Using the dynamical theory of NRS, the temperature and magnetic field dependence of the electric field gradient and magnetic hyperfine field on Ir nucleus have been determined for these compounds. In order to broaden the perspectives of NRS with the 73 keV resonance the first room temperature NRS on iridium metal is carried out. The results demonstrate NRS as a powerful research tool for the studies of iridium physics due to the high energy of the resonant photons and the high natural abundance of the $^{193}$Ir isotope under study, paving the way for studies of magnetism and electronic properties under extreme conditions.The second part of this work is dedicated to vibrational spectroscopy with Nuclear Inelastic Scattering (NIS). A sapphire backscattering monochromator was designed, installed and tested at the beamline. It provides high energy resolution due to the sub-mK temperature control, though the resolution is limited from theoretically proposed sub-meV to meV by the quality of currently available sapphire crystals. With this device the energy resolution of 1.3(1) meV at 23.88 keV and of 3.2(4) meV at 37.13 keV was achieved. Following this development, the vibrational spectra of antimony in defect pyrochlore Ag-Sb-O compounds have been measured by means of NIS at 37.13 keV. Density of phonon states for the Sb(III) and for the Sb(V) site has been revealed. The difference in site-specific antimony modes illustrates the importance of lattice dynamics for the engineering of these compounds.
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