Bestimmung der Zwischengitterverteilung von Sauerstoffatomen mittels Elektronenbeugung an einkristallinen Urandioxydschichten

Abstract

Evaporated monocrystalline films of uranium dioxide display superstructure diffraction diagrams when they are heated up to 250–600° C in the electron diffraction camera and then exposed to oxygen at 10 −3 torr pressure. Interpretation of the diagrams shows that under the specified experimental conditions a superstructure is formed the unit cell of which contains 4 × 4 × 1 unit cells of the UO 2 structure ( a=5.47 A ̊ ). This superlattice cell with its basic 64 uranium and 128 oxygen atoms contains a further 12 oxygen atoms, so that the composition is UO 2.19. The exact positions of these additional atoms is specified and the conclusion is drawn that during oxidation from UO 2 to UO 2.19 the additional oxygen atoms are not distributed uniformly through the lattice, but that groups of three closely neighbouring atoms are formed; the balance of attractive and repulsive forces is such that the additional atoms do not lie exactly in the ideal interstitial positions.