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Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis./
Author:	Yang, Long.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	276 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-07, Section: B.
Contained By:	Dissertations Abstracts International82-07B.
Subject:	Condensed matter physics. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28152574
ISBN:	9798557081450

Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis.
Yang, Long.

Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 276 p.

Source: Dissertations Abstracts International, Volume: 82-07, Section: B.

Thesis (Ph.D.)--Columbia University, 2021.

This item must not be sold to any third party vendors.

Quantum materials have strong electron correlation effects. According to the "structure-property" relationship, it is crucial to study the structure of quantum materials to better understand and manipulate the physical properties. The quantum effects are significant at the atomic microscopic length scale, which is not feasible to be studied by the average long-range structure measurement from conventional diffraction methods. Instead the local structure probe, pair distribution function (PDF) analysis, can effectively reveal the mystery of local structure, which is sensitive to the local behavior rather than the bulk average properties. In this thesis, the joint neutron and x-ray PDF (NXPDF) method is implemented. Because of their different interactions with matters, a combination of neutron and x-ray scattering can help comprehensively understand the atomic structures of some strongly correlated d- and f-electron systems that are difficult to be studied alone.Though powerful for understanding the structure of complex materials, performing the PDF modeling and structure refinement usually requires a lot of work on model selection for candidate structures. To address this problem, a new approach is developed to obtain candidate atomic structures from NXPDF, called structure-mining, in a highly automated way. It fetches, from open structural databases, all the structures meeting the experimenter's search criteria and performs structure refinements on them without human intervention. Tests on various material systems show the effectiveness and robustness of the algorithm in finding the correct atomic crystal structure. It works on crystalline and nanocrystalline materials including complex oxide nanoparticles and nanowires, low-symmetry and locally distorted structures, and complicated doped and magnetic materials. The examples of applying structure-mining method to identify the local structures of Pr6O11, BaFexTi1−xO3, and MgTi2O4 materials, which have strongly correlated d- and f-orbital electronic states under study in the thesis, are shown as well. This approach could greatly reduce the traditional structure searching work for quantum materials as well as other systems.The NXPDF method is first applied to the praseodymium oxide semiconductor nanoparticles to investigate the local structure behavior accompanied by the loss of electrical conductivity when temperature changes. The Pr and O sublattices can be determined precisely by x-ray and neutron PDF, respectively, because of their distinct x-ray atomic form factors and neutron scattering lengths. A combination of a highly ordered structure motif and a locally distorted oxygen deficient structure environment can describe the measured NXPDFs reasonably well. The iron doped barium titanate BaFexTi1−xO3 system is also investigated using PDF methods for studying the multiferroic behavior in the nanocrystals, which are synthesized near room temperature. The perovskite structure is established to be non-centrosymmetric, consistent with predictions of the pseudo-Jahn-Teller effect being the underlying cause of off-center displacements of B-site (Ti and doped Fe) atom, lowering the symmetry in order to make additional overlap between the 3d orbital of Ti and neighboring O atoms to create π molecular orbitals. This triggers the spontaneous polarization of the crystal. The PDF results establish that Fe is successfully doped into the ferroelectric BaTiO3 phase, and the measured dielectric and magnetic properties also validate the multiferroic behavior of the synthesized BaFexTi1−xO3 nanocrystals. In addition, the NXPDF analysis is also conducted on the MgTi2O4 system to track the evolution of the local atomic structure across the temperature-dependent metal-insulator transition, and the results reveal that local tetragonality is persistent, preformed with reduced magnitude, deep in the metallic and on average cubic regime. Significantly, the high temperature local state revealed by PDF is not continuously connected to the orbitally ordered band insulator ground state and the transition cannot be characterized as a trivial order-disorder type. The shortest Ti-Ti bond lengths corresponding to spin singlet dimers shift to longer distances on warming but are still shorter than those seen in the cubic average structure. These seemingly conflicting observations could be reconciled within the model of a local fluctuating t2g orbital-degeneracy-lifted (ODL) precursor state. These results undoubtedly establish the effectiveness of the joint neutron and x-ray PDF analysis to investigate the structure-property relationship on the sub-nanometer length scale of strongly correlated electron materials, utilizing the complementary structure information obtained from neutron and x-ray scattering.

ISBN: 9798557081450Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Local structure

Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis.
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245 1 0 $a Local Structural Insights into Exotic Electronic States in D- and F-Electron Oxides with Joint Neutron and X-ray Pair Distribution Function Analysis.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2021
300 $a 276 p.
500 $a Source: Dissertations Abstracts International, Volume: 82-07, Section: B.
500 $a Advisor: Billinge, Simon J. L.
502 $a Thesis (Ph.D.)--Columbia University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Quantum materials have strong electron correlation effects. According to the "structure-property" relationship, it is crucial to study the structure of quantum materials to better understand and manipulate the physical properties. The quantum effects are significant at the atomic microscopic length scale, which is not feasible to be studied by the average long-range structure measurement from conventional diffraction methods. Instead the local structure probe, pair distribution function (PDF) analysis, can effectively reveal the mystery of local structure, which is sensitive to the local behavior rather than the bulk average properties. In this thesis, the joint neutron and x-ray PDF (NXPDF) method is implemented. Because of their different interactions with matters, a combination of neutron and x-ray scattering can help comprehensively understand the atomic structures of some strongly correlated d- and f-electron systems that are difficult to be studied alone.Though powerful for understanding the structure of complex materials, performing the PDF modeling and structure refinement usually requires a lot of work on model selection for candidate structures. To address this problem, a new approach is developed to obtain candidate atomic structures from NXPDF, called structure-mining, in a highly automated way. It fetches, from open structural databases, all the structures meeting the experimenter's search criteria and performs structure refinements on them without human intervention. Tests on various material systems show the effectiveness and robustness of the algorithm in finding the correct atomic crystal structure. It works on crystalline and nanocrystalline materials including complex oxide nanoparticles and nanowires, low-symmetry and locally distorted structures, and complicated doped and magnetic materials. The examples of applying structure-mining method to identify the local structures of Pr6O11, BaFexTi1−xO3, and MgTi2O4 materials, which have strongly correlated d- and f-orbital electronic states under study in the thesis, are shown as well. This approach could greatly reduce the traditional structure searching work for quantum materials as well as other systems.The NXPDF method is first applied to the praseodymium oxide semiconductor nanoparticles to investigate the local structure behavior accompanied by the loss of electrical conductivity when temperature changes. The Pr and O sublattices can be determined precisely by x-ray and neutron PDF, respectively, because of their distinct x-ray atomic form factors and neutron scattering lengths. A combination of a highly ordered structure motif and a locally distorted oxygen deficient structure environment can describe the measured NXPDFs reasonably well. The iron doped barium titanate BaFexTi1−xO3 system is also investigated using PDF methods for studying the multiferroic behavior in the nanocrystals, which are synthesized near room temperature. The perovskite structure is established to be non-centrosymmetric, consistent with predictions of the pseudo-Jahn-Teller effect being the underlying cause of off-center displacements of B-site (Ti and doped Fe) atom, lowering the symmetry in order to make additional overlap between the 3d orbital of Ti and neighboring O atoms to create π molecular orbitals. This triggers the spontaneous polarization of the crystal. The PDF results establish that Fe is successfully doped into the ferroelectric BaTiO3 phase, and the measured dielectric and magnetic properties also validate the multiferroic behavior of the synthesized BaFexTi1−xO3 nanocrystals. In addition, the NXPDF analysis is also conducted on the MgTi2O4 system to track the evolution of the local atomic structure across the temperature-dependent metal-insulator transition, and the results reveal that local tetragonality is persistent, preformed with reduced magnitude, deep in the metallic and on average cubic regime. Significantly, the high temperature local state revealed by PDF is not continuously connected to the orbitally ordered band insulator ground state and the transition cannot be characterized as a trivial order-disorder type. The shortest Ti-Ti bond lengths corresponding to spin singlet dimers shift to longer distances on warming but are still shorter than those seen in the cubic average structure. These seemingly conflicting observations could be reconciled within the model of a local fluctuating t2g orbital-degeneracy-lifted (ODL) precursor state. These results undoubtedly establish the effectiveness of the joint neutron and x-ray PDF analysis to investigate the structure-property relationship on the sub-nanometer length scale of strongly correlated electron materials, utilizing the complementary structure information obtained from neutron and x-ray scattering.
590 $a School code: 0054.
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Materials science. $3 543314
653 $a Local structure
653 $a Nanomaterials
653 $a Pair distribution function
653 $a Powder diffraction
653 $a Structure-property
690 $a 0794
690 $a 0611
710 2 $a Columbia University. $b Materials Science and Engineering. $3 1684290
773 0 $t Dissertations Abstracts International $g 82-07B.
790 $a 0054
791 $a Ph.D.
792 $a 2021
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28152574