Evaluation of some basic positron-related characteristics of SiC

First-principles electronic structure and positron-state calculations for perfect and defected 3C- and 6H-SiC polytypes of SiC have been performed. Monovacancies and divacancies have been treated; the influence of lattice position and nitrogen impurities have been considered in the former case. Positron affinities and binding energies have been calculated; trends are discussed, and the results compared with recent atomic superposition method calculations. Experimental determination of the electron and positron work functions of the same 6H-SiC allows an assessment of the accuracy of the present first-principles calculations, and to suggest further improvements. © 1996 The American Physical Society.Peer reviewe

STUDIES OF THE Cu-Mn SYSTEM

The superstructures Cu 3 Mn and Cu 5 Mn have been characterized for the first time by X-ray and differential scanning calorimetry measurements. In addition, positron lifetime measurements are presented in order to show the defect structure of these alloys. It turned out that the annealing behaviour is equal for the two different alloys and the two different deforming processes. An annealing temperature of 300°C is not sufficient to obtain a defect free state

Long-Time Aging Behaviour of the Alloy Al-2024 Characterized by Positron Annihilation Spectroscopy

The reconstruction of the precipitation structure after solution treatment has been investigated by positron annihilation spectroscopy. In this study the behaviour of samples taken from an aircraft "Airbus 300", being in operation for 18 years, is compared to a reference material supplied by Alcoa. The results of position annihilation spectroscopy show that there are no significant differences in both materials. This finding is in agreement with the results obtained from other methods within the scope of the general research program which points to a materials behaviour as predicted for a safe operation of this type of aircraft

Studies of the Cu-Mn System

The superstructures Cu$\text{}_{3}$Mn and Cu$\text{}_{5}$Mn have been characterized for the first time by X-ray and differential scanning calorimetry measurements. In addition, positron lifetime measurements are presented in order to show the defect structure of these alloys. It turned out that the annealing behaviour is equal for the two different alloys and the two different deforming processes. An annealing temperature of 300°C is not sufficient to obtain a defect free state