High-performance thermoelectric materials





    
                                                                                 
DOI:10.1051/e3sconf/20171401032,  DOI:10.3390/app9071511
The increasing global energy demand along with environmental concerns of using fossil fuels has spurred vigorous research on various alternative energy technologies. Thermoelectric (TE) technologies are a particularly attractive option due to their direct heat to electricity energy conversion. TE devices are made of degenerate semiconductors or semimetals known as TE materials. A material’s TE performance at temperature T is gauged by the dimensionless figure of merit, zT = σS2T/(κL + κe), where σ, S, κL, and κe are the electrical conductivity, Seebeck coefficient, and lattice and electronic thermal conductivities, respectively. Despite no known theoretical upper limit of zT, state-of-the-art TE materials usually exhibit a maximum zT below 3.0 due to the inherently counterindicated {σ, S, κe} and unsatisfactory κL. As a result, the energy conversion efficiency of state-of-the-art TE devices is far below the Carnot efficiency and unable to rival those of other sustainable energy conversion technologies, thereby impeding the broader use of TE technology. In this regard, developing high-performance TE materials has been at the core of TE research as they have great potential to be applied in highly efficient cooling, energy scavenging, and sensing systems. In the past two decades, the exploitation of new materials and innovating engineering strategies have substantially increased the zT values of TE materials. Despite newly discovered materials and many recent advances, the selection rules of parent compounds and the subsequent doping, alloying, and compositing routine have remained unchanged for a few decades. Therefore, there is a pressing demand for conceptual and methodological breakthroughs toward next-generation TE materials.
Thermoelectric research is not only a course of materials by discovery but also a seedbed of novel concepts and methodologies. Our lab focuses on developing new thermoelectric materials and welcomes partners interested in developing high ZT thermoelectric materials.

Lattice dynamics of superionic thermoelectrics











We know that materials with complex crystal structure, weak interatomic bonding, strong anharmonicity, and glassy structure usually have lower κL. The κL can be further diminished by employing hierarchical microstructures, multinary alloying, or implementing point defects, dislocations, and interfaces. However, when the phonon mean free path (MFP) is reduced to the interatomic spacing by various phonon scattering mechanisms, the κL will approach the amorphous limit, the ceiling of disrupting lattice periodicity and structural ordering. In this context, the emerging concept of phonon-liquid electron-crystal provides a feasible solution for further phonon engineering. Superionic thermoelectrics and organic-inorganic hybrid perovskites exhibit crystal-liquid duality. They consist of a rigid sublattice holding fixed atoms and a dynamic sublattice in which delocalized cations can jump/rotate from one equilibrium position to another in a very short time, like a liquid. The coexistence of a crystalline-like response in semiconducting band transport and a liquid-like response in phonon transfer provides us with an excellent opportunity to achieve incredible zT values.
Our lab focusses on developing high-efficiency hybrid perovskite thermoelectrics and searching for new superionic thermoelectrics based on Zintl concept. Also, we intend to unveil the exotic lattice dynamics in such a crystal-liquid hybrid lattice that leads to a more liquid-like thermal conductivity. We will carry out temperature-dependent inelastic neutron scattering (INS) measurements on large single crystals to provide direct information about the phonon dispersion relations and lifetime. Combining first-principles lattice dynamics calculations and molecular dynamic simulation with our INS data, we will get a deeper insight into the multi-phonon interactions, phonon softening, electron-phonon coupling, and will know how superionic cations affect thermoelectric properties.

Crystal structure and Single crystal growth & design









To study the fundamental properties of materials, our laboratory focuses on the development of various single crystal growth technologies, including chemical vapor deposition (CVD), physical vapor transport (PVT), Bridgman method, solvent-related methods, ultra-high vacuum epitaxy, etc. We welcome partners who are interested in BIG single crystal growth to join us.