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Center for Nonlinear Studies |
Ceramic materials display a wide variety of valuable properties, such as ferroelectricity, superconductivity, and magnetic ordering, due to the partially covalent bonds which connect the cations and anions. While many breakthroughs have been made by mixing several cations on the same site of a ceramic crystal, the equivalent mixed-anion ceramics have not received nearly as much attention, despite the key role the anion plays in the materials’ properties. In this presentation, I will describe our theoretical studies of using anion vacancies in oxides and anion substitution in oxyfluorides and oxynitrides to either tune existing properties or even obtain new functionalities.
First, I will present results of a joint theoretical and experimental investigation resolving the atomic-scale location of individual oxygen vacancies in the high-temperature superconductor YBa2Cu3O7-x (YBCO), where vacancies are known to play a pivotal role in controlling the superconducting properties. Second, I will present our theoretical results predicting low-temperature fluorination of anion-deficient iron and manganese oxides as a strategy to achieve multiferroic compounds with simultaneous ferroelectric and magnetic ordering. Finally, I will describe a strategy to achieve high-performance, ferroelectric semiconductors using oxynitrides. We propose a new class of stable tin oxynitrides, which have tunable bandgaps spanning the entire visible spectrum, light effective mass of electrons that promotes electric conductivity, and have a non-centrosymmetric structure with a large, potentially switchable, spontaneous polarization . These examples demonstrate the power of anion engineering to create new functional ceramics with desirable properties.
Host: Galen Craven