Abstract
A hole center on an oxygen adjacent to one aluminum and one phosphorous was detected and analyzed in natural and X-ray irradiated brazilianite. The slightly anisotropic 27 Al shfs splitting is larger than in many other hole centers in which the Al is a lower valency impurity ion with only a coordinative bond to an oxygen lone pair. The hole is trapped at an oxygen with particularly long bond distances to one P and two Al. Thus one structural Al must be substituted by a presumably divalent cation of yet unknown nature. No optical absorption is associated with this center, therefore the large distortion of the coordination polyhedra must be responsible for absence of a light-induced hole transfer between different oxygen ions. Comparison with other systems suggests that the energy differences for other configurations of the hole center are also too high to allow thermal hopping of the hole at or below room temperature. Possible mechanisms for formation and destruction of this center are deduced from experimental results.
© 1946 – 2014: Verlag der Zeitschrift für Naturforschung
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