High-pressure synthesis of the 4d and 5d transition-metal oxides with the perovskite and the perovskite-related structure and their physical properties
| dc.contributor.advisor | Zhou, Jianshi | en |
| dc.contributor.advisor | Goodenough, John B. | en |
| dc.contributor.committeeMember | Manthiram, Arumugam | en |
| dc.contributor.committeeMember | Lozanne, Alex De | en |
| dc.contributor.committeeMember | Markert, John T. | en |
| dc.creator | Cheng, Jinguang | en |
| dc.date.accessioned | 2010-09-30T19:56:20Z | en |
| dc.date.available | 2010-09-30T19:56:20Z | en |
| dc.date.available | 2010-09-30T19:56:33Z | en |
| dc.date.issued | 2010-05 | en |
| dc.date.submitted | May 2010 | en |
| dc.date.updated | 2010-09-30T19:56:33Z | en |
| dc.description | text | en |
| dc.description.abstract | A Walker-type multianvil high-pressure facility is capable of high-pressure syntheses and measurements beyond 10 GPa and has been utilized in my research to synthesize the 4d Ruthenium and Rhodium and the 5d Iridium oxides with the perovskite-related structures. Under high-pressure and high-temperature conditions, these families of oxides can be enlarged to a great extent so that enables us not only to address the long-standing problem about ferromagnetism in the perovskite ruthenates but also explore new phenomena associated with the structural and electronic properties in the iridates and rhodates. In the perovskite ruthenates ARuO₃ (A= Ca, Sr, and Ba), a systematic study of the variations of the ferromagnetic transition temperature T[subscript c] and the critical isothermal magnetization as a function of the average A-site cation size and the size variance as well as external high pressures reveals explicitly the crucial role of the local lattice strain and disorder on T[subscript c] and the nature of the localized-electron ferromagnetism. However, such a steric effect is dominated by the electronic effect in another perovskite ruthenate PbRuO₃, which is a paramagnetic metal down to 1.8 K and undergoes a first-order structural transition to a low-temperature Imma phase at Tt [almost equal to] 90 K. Bandwidth broadening due to orbital hybridization between Pb-6s and Ru-4d plays an important role in suppressing the ferromagnetism in the Sr1-zPbzRuO₃ system. The high-pressure sequence of the 9R-BaIrO₃ was explored and three more polytypes, i.e. 5H, 6H and 3C, were identified under 10 GPa. With increasing fraction of the corner- to face-sharing IrO₆/₂ octahedra, the ground states of BaIrO₃ evolve from a ferromagnetic insulator with T[subscript c] [almost equal to] 180 K in the 9R phase to a ferromagnetic metal with T[subscript c] [almost equal to] 50 K in the 5H phase, and finally to an exchange-enhanced paramagnetic metal near a quantum critical point in the 6H phase. In addition to the perovskite SrRhO₃, a new 6H polytype was synthesized for the first time under high pressure and a pressure-temperature phase diagram was given for the 6H-perovskite transformation. Restoration of the Curie-Weiss behavior in the high-temperature magnetic susceptibility [chi](T) of the perovskite SrRhO₃ resolves the puzzle about unusual dependence of [chi]⁻¹ [symbol] T² reported earlier and highlights the importance of spin-orbit coupling in the 4d and 5d transition-metal oxides. | en |
| dc.description.department | Materials Science and Engineering | |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.uri | http://hdl.handle.net/2152/ETD-UT-2010-05-834 | en |
| dc.language.iso | eng | en |
| dc.subject | High-pressure synthesis | en |
| dc.subject | Perovskite oxides | en |
| dc.subject | Ruthenates | en |
| dc.subject | Iridates | en |
| dc.subject | Rhodates | en |
| dc.title | High-pressure synthesis of the 4d and 5d transition-metal oxides with the perovskite and the perovskite-related structure and their physical properties | en |
| dc.type.genre | thesis | en |
| thesis.degree.department | Materials Science and Engineering | en |
| thesis.degree.discipline | Materials Science and Engineering | en |
| thesis.degree.grantor | University of Texas at Austin | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |