Functional Inorganic Materials at UMD
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March 2018 Our work on new layered transition metal chalcogenides was published in Physical Review B titled "Frustrated magnetism in the tetragonal CoSe analog of superconducting FeSe".
February 2018 Our work on solid-state oxygen storage materials was published in Journal of Materials Chemistry A titled "In situ diffraction studies on reversible oxygen uptake and release in AFe2O4+δ ( A = Lu, Yb, Y, In)".
October 2017 Congratulations to Rishvi Jayathilake for winning the student poster prize at the 75th Annual Pittsburgh Diffraction Conference! Her poster was titled "Oxygen Storage Properties of RFe2O4 (R = Lu, Yb, Y, and In)".
June 2017 Our perspective article on layered metal chalcogenides was published in Chemistry of Materials as part of their Up-and-Coming series. "Tetrahedral Transition Metal Chalcogenides as Functional Inorganic Materials".
June 2017 Congratulations to Dan for successfully defending his PhD thesis "Structural and Chemical Factors Governing Anion Reactivity in Perovskite Oxides".
May 2017 Congratulations to Amber for successfully defending her PhD thesis "Frustrated Magnetism and Electronic Properties of Hollandite Oxide Materials".
May 2017 Our work on an interesting metal-to-insulator transition in a metal oxide was published in Journal of Materials Chemistry C titled "Metal-insulator transition tuned by magnetic field in Bi1.7V8O16 hollandite".
March 2017 Our work on superconducting and new layered iron suflides was published as an Edge Article in Chemical Science titled "Superconductivity and magnetism in iron sulfides intercalated by metal hydroxides".
Solid-state materials can transform how we communicate, utilize energy, and store information. Before being integrated into exciting applications, every advanced material must first be developed by fundamental science and engineering. At the University of Maryland, our group uses a multidisciplinary approach for the preparation and study of functional inorganic materials. We design and synthesize energy-related materials and novel quantum materials, where interactions at the atomic scale have profound consequences for their macroscopic properties. With advanced neutron measurements of our materials, we investigate what is so unique about their crystal structures that give rise to their advanced physical properties. Finally, we have strong collaborations with UMD Physics and the nearby National Institute of Standards and Technology (NIST) to deepen the impact of our science. Below are specific directions our group currently pursues.
Research area 1: Tetrahedral transition metal chalcogenides for superconductivity and magnetism
The development of superconductivity at a high enough temperature would revolutionize the electrical grid by creating highly efficient power lines. In addition to this extraordinary property, superconductors can create large, stable magnetic fields, which already have utility in medical technologies such as magnetic resonance imaging (MRI). To fulfill potential future applications, we must find compounds with optimal properties such as a high enough Tc to make practical devices. Our group synthesizes transition metal chalcogenides with layered-type structures in order to prepare new superconductors or related physical properties. With advanced measurements that include synchrotron X-rays and neutrons, we study the key structure-property relationships of our superconducting materials. In addition, we find novel chemical route towards the preparation of single crystals of our materials. Common to all of our superconductors is the similarity in their crystal structures. In these chalcogenides, the M2+ ions are in tetrahedral coordination, and those MCh4 tetrahedra are edge-sharing. For the 2D materials, we are primarily interested in how to build new heterestructures to manipualte the magnetism and superoconductivity. For the 3D materials, we are interested in the fundamental interactions between the magnetism and itinerant electrons. In all cases, we are looking to find new synthetic routes towards new materials and single crystal growth. (Click here) to see our our latest papers on these materials. Below, a schematic of the topochemical reactions to achieve different phases of layered iron chalcogenides.
Research area 2:Mixed-valence microporous oxides for novel magnetism and energy-related applications
Our goal is to prepare new metal oxides with microporous and mesoporous structures, some of which are known from naturally occurring minerals such as hollandite and todorokite. The 1D channels are constructed purely of edge-sharing MO6 octahedra where M is a transition metal and cations such as K+ and Ba2+ reside in those channels. We have focused on Mn-based oxides for magnetic properties, Ti-based oxides for catalytic and energy storage applications, and V-based oxides for electrical transport properties such as metal-to-insulator transitions. The hollandite-type structure is especially versatile and can readily accommodate several members of the transition metal series, which allows for facile doping to tune the electronic and magnetic properties. Click here to see our our latest paper on titanate hollandites and here for the Mn-based hollandites. Below, a schematic demonstrating the various structurally-related transition metal oxides possible in this family of compounds.
Research area 3: Transition metal oxides for energy conversion
In addition to studying quantum materials, we also study energy conversion materials. An alternative method to convert fuels into energy besides combustion with air is to react them with solid metal oxides at elevated temperatures (> 600 oC). Since these compounds are depleted of their oxygen content after reaction with a fuel, they will have to be regenerated in air in order to restore the amount of oxygen in the crystal lattice. Hence, these materials are "oxygen sponges" known as oxygen storage materials (OSMs). As illustrated below, these OSMs are the key participants in what is known as a Chemical Looping Cycle (CLC). Successful and widespread use of CLC reactors would cut down on the emissions of the most damaging greenhouse gas, CO2. CLC reactors also preclude expensive gas separations of O2 and N2 from CO2. In our laboratory we synthesize OSMs by focusing on transition metal oxides with the perovskite crystal structure (ABO3 and layered structures with formula AB2O4. We study their performance under CLC conditions while monitoring their chemical composition and crystal structures. To do this, our group performs extensive in-situ reactions with both neutrons and synchrotron X-rays to study oxides. From these in situ and fast diffraction experiments, we formulate the chemical and crystallographic parameters that influence the merits of a perovskite and other transition metal oxides such as oxygen storage capacity and the reaction kinetics. Below, a schematic of a chemical looping reaction involving a perovskite oxide and the the in-situ synchrotron diffraction with patterns collected every 6 seconds.
Research area 4: Uncovering Ferrotoroidic Ordering through Targeted Materials Synthesis and Polarized Neutron Diffraction
Our goal is to prepare and study the magneto-structural properties of what have been considered the missing fourth class of primary ferroics--ferrotoroidics. In these materials, the magnetic space groups allow simultaneous magnetic ordering and electric polarization, i.e. breaking both time-reversal and space-inversion symmetries. In addition, the spins of the magnetic moments in the crystal lattice arranged head-to-tail, which induces a perpendicular toroidal moment. Since this toroidization produces ferroic domains, ferrotoroidicity is consequently considered a primary ferroic order. Our work is to explore the materials that exhibit ferrotoroidicity by synthesizing those that possess the required symmetries and magneto-electric properties, and developing the polarized neutron diffraction instrumentation needed to elucidate this type of order.