Annual Report 1995

Report 3 / 3

Investigations of electric-field-gradients in amorphous and crystalline SiO₂-structures

P. Friedsam, M. Forker, Ch. Schön^a, R. Vianden

^a Institut für Anorganische Chemie, Universität Bonn

Contents:

The perturbed angular correlation (PAC) method yields information about the nearest neighbor shells of a probe atom via the electric field gradients produced by deviations from the cubic symmetry of its surrounding.

In a program aimed at the study of the short range order in amorphous anorganic compounds the PAC probe ¹¹¹In was implanted into crystalline and amorphous SiO₂. Subsequently the samples were isochronously (T_hold=10 min) annealed at different temperatures up to 1200°C in order to anneal the implantation damage and to observe differences in the incorporation of ¹¹¹In into the crystalline and amorphous SiO₂.

The experimental results have been compared to theoretically calculated PAC spectra based on electric field gradients obtained from the point charge model. The positions of the ions resulted from a simulation of local atomic configurations in a SiO₂ cluster of 21 Si-atoms (4+), 25 O-atoms (2-), 34 O-atoms (1-) and 1 In-atom after using a "simulated annealing" optimisation method. [1]

References:

[1] P. Friedsam, M. Forker, Ch.Schön, R. Vianden; Verhandlung: DPG(VI) 31, 1140 (1996)