Effects of external stress on defect complexes in semiconductors
Crystal field gradients that exist at lattice sites in solids depend on the symmetry of charge distribution around atomic sites. The charge symmetry could be broken either by the presence of impurity complexes in the host matrix or by external stress on the samples, which leads to an observable magnitude of electric field gradients (EFGs). The perturbed γ–γ angular correlation (PAC) method is employed here to investigate the effect of uniaxial stress on 111Cd sites in crystalline doped semiconductors.
Intrinsic and extrinsic defects in semiconductors studied by perturbed γγ angular correlation spectroscopy
The application of the perturbed γγ angular correlation technique as an analytical tool for the characterisation of atomic defect configurations is discussed. Using the radioactive probe atom111In/111Cd, recent results on the compensation of acceptor and donor atoms in different II–VI semiconductors will be discussed, in particular the role of the cation vacancy defect.
Techno-economic analysis of solar thermal power plants using liquid sodium as heat transfer fluid
Abstract Solar thermal power plants with central receiver and thermal storage are expected to be one key technology in future electricity generation, because they are renewable and due to the thermal storage independent of the current solar radiation. State-of-the-art solar power plants often use molten nitrate salts as heat transfer fluid. The use of liquid sodium instead leads to lower electricity generation costs. Sodium has a high thermal conductivity and thus large heat transfer rates are possible. Hence, a smaller absorber surface is sufficient for the same thermal power. As a result, the sodium receiver achieves a higher efficiency at lower investment cost. Additionally, the aiming strategy, which reduces the peak heat flux on molten salt receivers isn’t necessary for sodium. Even at high heat flux densities, the absorber tubes will be cooled sufficiently due to the high heat transfer coefficients. Therefore, the sodium receiver in this analysis is designed for one single aim point, resulting in a heat flux density of q mean = 1.06 MW / m 2 and q peak = 2.99 MW / m 2 . The state-of-the-art system with molten salt considers q mean = 0.51 MW / m 2 and q peak = 1.0 MW / m 2 . The presented techno-economic analysis of two sodium based concepts compared to a reference system with molten salt results in up to 16% lower electricity generation costs.