Thermal transport in inorganic-organic frameworks

• Applicant: Dr. Gregor Kieslich
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 253095348

During the last decades the research field of hybrid inorganic-organic frameworks has evolved into one of the fastest growing areas in materials chemistry. Usually divided into the class of (i) nanoporous hybrid frameworks, commonly known as metal-organic frameworks (MOFs) and (ii) dense hybrid frameworks, the virtually unlimited range of organic linkers can design frameworks for many applications, such as gas storage, catalysis, chemical sensing and controlled drug release. However, studies have focused on structural-, adsorption- and diffusion properties of framework materials, rather than on thermal transport characteristics. In particular, most of the properties exhibit an ideal working temperature and are highly sensitive towards unintended thermal fluctuations, e.g. emerging during absorption and desorption processes. Therefore the knowledge about the thermal properties is essential for the intended application. The here proposed project focuses on the investigation of the thermal transport characteristics of inorganic-organic hybrid materials. The first step towards a comprehensive understanding of thermal transport is the measurement of the temperature dependent thermal conductivity and the modeling within established concepts. In order to achieve this goal, the 3 technique has been identified as optimal technique, which allows the accurate measurement of the low temperature thermal conductivity of small single crystals.In this context Zeolitic imidazolate frameworks (ZIFs) and hybrids with perovskite-like architecture (ABX3) are a reasonable starting point for the first investigations. Their huge topological diversity (ZIFs) and temperature driven magnetic and structural transitions (ABX3 frameworks) allow detailed examinations of the influence of single building blocks on the thermal conductivity. Based on these results, the validity of known concepts for the modeling of the thermal conductivity will be verified and validated for other hybrid families such as cerium oxalate-formate frameworks, copper phosphono acetates and the group of isoreticular frameworks.The final and most exciting task within this project is the use of the acquired knowledge for the investigation and the optimization of the thermoelectric properties of semiconducting inorganic-organic frameworks. Due to the very low thermal conductivity on the one hand and the periodic structure on the other hand inorganic-organic hybrids represent characteristics of both amorphous and crystalline materials, and thus, inorganic-organic semiconducting hybrids fulfil the concept of a phonon-glass electron-crystal which describes the best thermoelectric material. Therefore this project combines both fundamental aspects and application oriented research in the area of hybrid inorganic-organic frameworks and will not only make contributions to the understanding of thermal transport in hybrid materials, but will also contribute to the field of thermoelectric research.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Anthony K. Cheetham