This research project focuses on the syntheses, structural characterization, and physical properties of new reduced rhenium and molybdenum oxide/organic hybrids that possess a range of low dimensional M-O-M' (M = Re or Mo, M' = late transition metal) and M-O-M bonded networks. The synthetic efforts will advance the use of hydrothermal techniques to yield the new reduced hybrids with electronic properties, and/or metal-metal bonding, that can also be dynamically coupled to selective small-molecule intercalation and redox activity. The hybrid solids will represent a new type of multifunctional electronic material, and as well, will help lead to a deeper understanding of the electron-electron interactions that are responsible for magnetoelectric and superconducting properties in reduced rhenates and molybdates. Resultant abilities to control or tune the electron-electron interactions at the molecular/atomic level within a flexible framework hold great potential for directly enabling many new electronic device applications. The educational component reaches out to a large and diverse base of students at the K-8, undergraduate and graduate levels, and will provide for many valuable experiences (e.g. new classroom demonstrations and research article discussions) in solid-state chemistry. The project will also provide research students with valuable professional training in advanced research techniques, including in solid-state syntheses, characterization, and physical property measurements.
Many future solid-state electronic devices are currently envisioned but that depend on a better understanding of the interactions between electrons within solids as well as how to utilize them in new multifunctional formats. For example, new research is necessary in order to learn how to employ the spin orientation of an electron to speed logic operations or to increase data storage capacities, or alternatively, for the resistance-free flow of electrical current. The research plans are centered around these overarching objectives, and aim toward a diverse range of flexible solid-state structures, based on the synergistic incorporation of organics into rhenium and molybdenum oxides, that possess an advanced functionality and flexibility that has never previously been utilized to probe electronic properties. Further, the multifunctional oxide/organic solids will represent a new and significant gateway for gaining control over the electronic properties at the molecular/atomic level, and that hold promise for enabling their application in future electronic devices. Research students will gain valuable professional training in advanced research techniques, involving solid-state syntheses, characterization, and physical property measurements. The project also includes the installment of cutting-edge research examples and demonstrations into the classroom, to help increase the understanding and awareness of the important contributions of solid-state chemistry research to society.
Research efforts have resulted in new flux synthesis routes to double-perovskites A2MM’O6 as well as new hydrothermal synthesis routes to M/M’/O/L (L = coordinating ligand) hybrid solids which contain two different types of transition metals. All compounds were used to take new physical property measurements, including optical, magnetic, thermal, photocatalytic and half-metallic properties. In the first area, this research uncovered a) new ways to synthetically control particle sizes with distinct morphologies, b) the ability to tune their magnetic and photocatalytic properties as a result of the flux synthetic conditions, and leading to c) a new and deeper understanding of their magnetic, magnetoresistance, and photocatalytic properties. These results have a broad impact, for example, in the field of magnetoresistance-based devices, especially in the area of intergrain tunneling type magnetoresistance (ITMR) in which a new theory was tested based on particle size and percent spin polarization. In addition, the area of photocatalysis has attracted much recent interest for using changes in particle sizes and morphologies to achieve high efficiencies for sunlight-to-fuel energy conversion. In the second area, several new M/M’/O/L hybrid solids have been discovered using hydrothermal synthetic methods and that contain low-dimensional M-M’-O chains and clusters. In this area, the research has led to new ways of a) using coordinating organic ligands to effect the metal-oxide structural feautures, b) tuning the new optical and magnetic properties as a function of the ligand coordination environments and structure, and c) selectively intercalating/de-intercalating molecular guest species within these compounds. The incorporation of coordinating organic ligands has enabled us to understand the relationships between the structural dimensionality, bandgap sizes, and magnetic properties, for example. These hybrid compounds have provided new insights into the origins of half-metallic and photocatalytic properties, and are of broad interest for enabling their applications in future electronic and photocatalytic devices. The research project has also provided many opportunities for graduate and undergraduate students to gain valuable professional training in solid-state syntheses, characterization techniques, and physical property measurements. The intellectual merits of the educational research efforts have included many different contributions, including the ongoing 1) annual development of new modules for the introduction of solid-state research demonstrations in undergraduate and graduate classrooms, 2) the development of a 4-week laboratory experience in the new CH444 ("Advanced Synthetic Techniques II") laboratory class that was offered during the Spring 2011 semester and is undergoing further revision, as well as 3) providing undergraduate research experiences for NCSU students during the academic school year and hosting REU students during the summer months. In addition, a new single-crystal X-ray diffractometer was acquired during this period and is currently maintained for training and use by upper-level undergraduate and graduate students. The educational components have reached out to a large and diverse base of students at the undergraduate and graduate levels and have provide them with important experiences in the emerging chemistry of solids. The research article and demonstration modules, while used locally in North Carolina, have been maintained on the web. Additional activities have included annual recruitment efforts to expand on our diverse base of students (graduates/undergraduates, ~15-30% minority; REU, 50% minority). The overall educational achievements of this research project have been to provide for a growing number of undergraduate and graduate students to experience and understand the fundamentals of solid-state chemistry and how these are brought out in research problems and eventually in future technologies.
