Yaniv Gelbstein and Moshe Dariel.png 

Dr. Yaniv Gelbstein studies Thermoelectrics in his lab. Thermoelectrics as a direct energy conversion method between heat and electricity is mainly used for electrical power generation and cooling applications. One of its major applications consists of using thermal energy (or heat) for power generation. It is based on Seebeck effect, stating that materials subjected to a temperature difference (DT), will develop a proportional internal electrical voltage (V). Another application is using of electrical current for cooling. The benefits of thermoelectric cooling / power generation include: high reliability (>250,000 hours), silent and vibration-less operation, low volume, minimal maintenance, lightweight, low life cycle costs, no compressed gasses or chemicals and environmentally friendly.

Development of efficient (>15%) thermoelectric converters (TEC) for utilizing of waste heat to large scale power generation applications is a very ambitious challenge, motivates leading multidisciplinary groups all around the world. Such TECs can be used for recovery of waste heat from exhaust of automotive engines and consequently reduction of the fuel consumption, big industrial plants, domestic heating, and others into electrical power generation. TECs with high overall efficiency convert heat directly into electricity without involving moving parts, not only decrease our reliance on fossil fuels but also actively counteract global warming effects, due to reduction of CO2 emission.

The major challenge of obtaining reliable beyond the state-of-the-art >15% efficient TECs is to combine high average thermoelectric figure of merit (ZT=a2s/k, where, a- Seebeck coefficient, s and k are the electrical and thermal conductivities, respectively, and T- the absolute temperature) materials with the converter's requirement of desired mechanical and long term stability characteristics at the operation temperatures.

The group of electronic materials in the Department of Materials Engineering in BGU has a long history of highly efficient novel thermoelectric materials development based on various materials' classes such as IV-VI compounds (e.g. PbTe and GeTe), half Heusler alloys (such as TiNiSn) and silicides (such as higher manganese silicides). By applying both optimal doping and nano-structuring approaches, maximal ZT values in the range of 1.2-1.8 were reached. Our thermoelectric related activities are/were funded by several international research grants including the Bi-national U.S – Israel Scientific Foundation (BSF), China-Israel Bi-national research grant, and a European Committee FP7 grant.

 

Energy conversion in nanoscale junctions

The thermo-electric (TE) effect is the conversion of a temperature gradient into an electric potential, a property which may be beneficial for future energy technology. Theoretically, molecular systems (i.e. Metal-molecule-metal junctions) can become superior thermoelectric converters and the thermoelectric response of a single-molecule junction have been measured in a set of impressive experiments. However, several of the experimental observations, including the value of the Seebeck coefficient and the observed large fluctuations, remain unexplained. Dr. Yonatan Dubi’s research is aimed at understanding the TE response of molecular junctions under various conditions, including the effects of junction geometry and contacts, presence of external fields (magnetic, microwave), and optical excitations. The main goal is to understand how energy is transported and converted in molecular junctions, and how it can be controlled and manipulated via external means. Other topics of interest include the theory of photo-voltaic conversion in molecular junctions, energy transport in DNA nano-junctions and electronic properties of complex materials.