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Structure-Property Relationships in Noncentrosymmetric Layered Perovskites

Sharits, Andrew R
http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Chemistry.
This work focuses on understanding the structure property relationships in layered perovskites. Certain properties such as ferroelectricity and luminescence are highly dependent upon the crystal structure and can be affected by structural distortions. This makes understanding the crystal structure imperative as it can be adverse or beneficial to the physical property of interest. Perovskites and layered perovskites are prone to structural distortions. As such it is important to understand the forces that drive distortions and how to control them so advantageous properties can be achieved. Chapter 2 discusses the luminescence of Eu3+ in the family of doubly ordered double perovskites NaREMgWO6 (RE = La, Gd, Y). NaYMgWO6, a new member of the family, was found to crystallize in P21 space group and is isostructural with NaGdMgWO6. Emissions characteristic of Eu3+ ions (5D0 -> 7F4, 3, 2, 1,0) were observed, with the most intense transition being the 5D0 -> 7F2 transition near 615 nm. Substitution of Eu3+ onto a more compressed RE site results in a blue shift of the charge transfer excitation band and an increase in the intensity of 5D0 -> 7F2 transition. These hosts display comparable if not better luminescence than Y2O3:Eu3+, a commonly used commercial standard, demonstrating their promise as red phosphors. Chapter 3 and Chapter 4 focus on understanding octahedral tilting, phase transitions and ferroelectric properties in Ruddlesden Popper (RP) phases. Data mining using the ICSD was performed and showed that RP phases typically crystallize in 4 common tilt systems: I4/mmm (a0a0c0), P42/mnm (a0b-c0), Cmcm (a-a-c0) and Cmc21 (a-a-c+). A sorting chart was created using the perovskite tolerance factor and the difference in ionic radii of the A-site cations. This led to the compounds, Ln2SrSc2O7 (Ln= La, Pr, Nd, Sm, Eu, Gd) and Sr3Zr2O7, which fall on the sorting chart in a location that suggests they should be susceptible to a polar distortion. Using distortion mode Rietveld refinements to analyze x-ray and neutron diffraction data, these compounds were discovered to crystallize in the polar space group, Cmc21. Detailed analysis of the phase transitions and ferroelectric properties were explored in La2SrSc2O7 and Nd2SrSc2O7. Chapter 5 focuses on the crystal structures of the family of Dion-Jacobson (DJ) phases, ALnNb2O7 (A=Cs, Rb; Ln= La, Pr, Nd). X-ray diffraction of the structure showed subtle splitting suggesting a lower symmetry than the parent space group P4/mmm. Neutron diffraction of RbLnNb2O7 showed a doubling of the c-axis whereas in the CsLnNb2O7 this was not observed. Synchrotron diffraction showed peak splitting in ALaNb2O7 that had not been observed in the x-ray data. It was found that the RbLaNb2O7 and CsLaNb2O7 crystallized in the nonpolar Cmca and Cmmm space groups, respectively. RbLnNb2O7 (Ln = Pr, Nd) and CsPrNb2O7 were found to crystallize in the polar space groups Ima2 and Pmc21. The driving force behind the octahedral tilting will be discussed.
Patrick Woodward (Advisor)
Yiying Wu (Committee Member)
Joshua Goldberger (Committee Member)
Robert Perry (Committee Member)
165 p.
Chemistry
layered perovskites; Ruddlesden-Popper phase; Dion-Jacobson phase

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Citations

  • Sharits, A. R. (2016). Structure-Property Relationships in Noncentrosymmetric Layered Perovskites [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735

    APA Style (7th edition)

  • Sharits, Andrew. Structure-Property Relationships in Noncentrosymmetric Layered Perovskites. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735.

    MLA Style (8th edition)

  • Sharits, Andrew. "Structure-Property Relationships in Noncentrosymmetric Layered Perovskites." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735

    Chicago Manual of Style (17th edition)

osu1480524956906735
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