TOPOCHEMICAL SYNTHESIS AND ELUCIDATION OF STRUCTURE-PROPERTY RELATIONSHIPS IN MAGNETIC KAGOM´E MATERIALS AND OTHER GEOMETRICALLY FRUSTRATED LATTICES

Na2Ti3Cl8;ferroelectric;Herbertsmithite;kagomé;topochemical;magnetism;frustration;Chemistry

Kelly, Zachary AndrewMcQueen, Tyrel M ;

Johns Hopkins University

关键词: Na2Ti3Cl8;    ferroelectric;    Herbertsmithite;    kagomé;    topochemical;    magnetism;    frustration;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/61045/KELLY-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Solid state chemistry is the study of extended crystalline solids containing ∼ 10^23 atoms. The overarching goal of solid state chemistry is to design new materials with specifically targeted properties. This is often accomplished by leveraging structure-property relationships. The focus of chapters 1 and 2 are to introduce key concepts for understanding structure-property relationships in solid state materials: electronic band theory, the concept of symmetry, the origins of magnetism, the phase transition theory, and methods. Refinement of these highly predictive and informative theoretical frameworks continues to push our understanding of materials and provides a pathway to discover novel emergent phenomena.Chapter 3 discusses the synthesis and properties of electron-doped synthetic Herbertsmithite, the first example of a doped canonical kagomé spin liquid. Previous pressure and doping studies have demonstrated that certain frustrated geometries display metallicity, but it has proven difficult to successfully introduce charges into definitively two dimensional spin liquids built on the kagomé or honeycomb lattice. By applying topochemical techniques, we were able to achieve it experimentally. We find that electron doping continuously suppresses the magnetism in the material without the appearance of superconductivity or related metallic phases. This is significantly different than the predictions of theory, which must be refined in light of our results.Chapter 4 reports the realization of an ideal S = 1 kagomé in Na2Ti3Cl8 . This quantum magnet undergoes a discrete two-step trimerization on cooling, transforming from a centrosymmetric high temperature phase to non-centrosymmetric, ferroelectric intermediate and low temperature phases via successive first order phase transitions and the formation of metal-metal bonds. We believe this is a novel mechanism to induce a proper ferroelectric phase transition at achievable temperatures driven through frustrated magnetism and metal-metal bonding. Development of new mechanisms to induce ferroelectricity remains rare. The unique kagomé to trimer ferroelectric transition with two discrete ferroelectric phases positions compounds that exhibit the same metal-metal bonding mechanism as Na2Ti3Cl8 to be highly viable for incorporation into the next generation of multifunction devices.Chapter 5 highlights the result of a collaboration with Prof. Kageyama at Kyoto University, Japan, supported by the NSF EAPSI fellowship. In Japan, I explored both low temperature techniques and high pressure syntheses to target new irridate compounds with a distorted honeycomb lattice. The compound Sr3CaIr2O9 has a unique corner-sharing connectivity of the iridium sub-lattice which forms a honeycomb structure. This corner-sharing allows for a specific type of magnetic exchange which could lead to the realization a magnetically frustrated system predicted to host the Kitaev spin liquid state. The issue is Sr3CaIr2O9 is non-magnetic since Ir is in the 5d 4 electronic state. This collaboration reviews the progress of reducing Sr3CaIr2O9 from the 5d^4 to 5d^5 in an attempt to realize the Kitaev spin liquid model.