Inorganic chalcogenide solids: from discovery to design and applications

David Wang Auditorium, 3rd floor Dalia Maydan Bldg.

The winner of  “Hershel and Hilda Rich Visiting Professorship 2017” – Prof. Mercouri G. Kanatzidis will be our guest during April 23-28, 2017 (Formal invitation will be sent later).

He will give 3 lectures during his visit, as follows:

24.4.17: Energy from waste heat: how thermoelectric materials are designed and used

26.4.17: Halide Perovskites: new high performance semiconductors

27.4.17: Inorganic chalcogenide solids: from discovery to design and applications

An ultimate goal in the field of chemistry is to identify and promote foundational and rational approaches needed to turn synthesis art into science by combining the exquisite predictability of organic synthesis with the high yields of solid state chemistry.  The search for new inorganic materials and efficient syntheses is therefore a fundamental goal of chemistry. In contrast to solid-state methods, inorganic syntheses in liquid fluxes permit bond formation, framework assembly and crystallization at lower temperatures due to facile diffusion and chemical reactions with and within the flux itself. The liquid fluxes are bona-fide solvents similar to conventional organic or aqueous solvents. These reactions can produce a wide range of materials, often metastable, from oxides to intermetallics, but typically the formation mechanisms are poorly understood. In this talk I will describe how we design, approach, perform, observe, understand, and engineer the formation of compounds from inorganic melts. I will focus on how novel chalcogenides can form using the fluxes but also design concepts such as the “counterion effect”, “dimensional reduction” and “panoramic synthesis”. For example in systems such as K-Cu-S and K-Sn-S compounds that span metallic and insulating behavior can be isolated. Common structural motifs within these materials systems belie structural precursors in the melt that may be controlled by tuning reaction conditions and composition. Using complementary techniques of in-situ x-ray diffraction we can create time-dependent maps of reaction space and probe the mobile species present in melts. An important link in our chemistry is the concept of a ‘functional group,’ a fragment of a few atoms that behaves predictably when combined with other functional groups or reagents.  When well defined building blocks are present and stable in the reaction, prospects for increased structural diversity and product control increase substantially. The stabilization of a particular building block is accomplished with the tuning of flux composition which controls Lewis basicity and redox potential. In such tunable and dynamic fluxes, synthesis can be directed towards new materials. I will highlight routes toward the ultimate goal of targeted materials synthesis by controlling inorganic melt chemistry.