Electrical conductivity and composition range of Ag2HgI4 between room temperature and 75°C

The composition range of α- and β-Ag₂HgI₄ near the transformation temperature is determined by X-ray diffraction. The electrical conductivity measured in the α-phase is nearly unaffected by deviation from stoichiometry. This is caused by a compensation of the composition dependences of σ₀ and of the activation energy E_A. From the experimental results the dependences of the entropy and of the Gibbs energy for migration of Ag-ions on temperature and on composition are estimated.     

CFD studies on the surge detection of a radial compressor flow by analyzing the unsteady secondary flow field

The objective of this investigation is the development of a reliable methodology allowing the accurate prediction of compressor surge. In this context a centrifugal compressor used in a commercial application with five main and five splitter blades, installed in regular passenger vehicles, is numerically analyzed. For this purpose a CFD analysis is conducted. The steady-state and unsteady secondary flow field is analyzed and studied by a frequency analysis to detect critical oscillations. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coupled substitution of gallium by magnesium and zirconium in single crystals of gadolinium gallium garnet

Single crystals of gadolinium gallium garnet in which the gallium ions on the octahedral sites were partially substituted by coupled substitution of magnesium and zirconium have been grown using the Czochralski technique. Single crystals of 36 mm in diameter and 100 mm in length corresponding to the formula Gd₃Ga_5-x-yMg_xZr_yO₁₂ have been obtained from melt compositions in which 0.1 ? x = y ? 0.7. The dislocation and inclusion densities of the single crystals are below 5 cm^-2. The lattice parameters increase linearly from 12.382 Å for gadolinium gallium garnet to 12.489 Å for x = y ≈ 0.54. The distribution coefficient increases in this concentration range from K_eff = 0.58 to K_eff = 0.89. Boules grown from melt compositions in which x = y ? 0.7 appear cloudy through precipitation of Gd₂Zr₂O₇ as a second phase.