First Principle Study and Optimal Doping for High Thermoelectric Performance of TaXSn Materials (X = Co, Ir and Rh)

In this paper, the full potential linearized augmented plane wave method implemented in the WIEN2K code with first principles-based density functional theory are used to investigate the structural, elastic, electronic and thermoelectric properties of TaCoSn, TaIrSn and TaRhSn. The structural and elastic constants are calculated using the generalized gradient potential developed by Perdew-Burke-Ernzerhof (GGA-PBEsol). The electronic structures are performed by means of GGA-PBEsol and improved by TranBlaha modified Becke-Johnson (TB-mBJ) potential. Our results show that the studied compounds are semiconductors with indirect gaps. On the other hand, we investigated the thermoelectric properties at different temperatures with respect to the chemical potential. The results show that the thermopower factors are more important for p-type doping than those for n-type doping and the maximum value of these factors indicates the optimal hole-doping level which gives rise to high thermoelectric performances of these materials. Finally, we note that the best thermopower values are found for the TaRhSn compound with optimal doping levels of (75.76, 175.60 and 238.92) x 1014 µW cm – 1 K – 2 s – 1 at temperatures of 300, 600, and 900 K, respectively

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA