Molecular modeling of electron traps in polymer insulators: Chemical defects and impurities

被引:340
作者
Meunier, M
Quirke, N [1 ]
Aslanides, A
机构
[1] Univ London Imperial Coll Sci Technol & Med, Dept Chem, S Kensington SW7 2AY, England
[2] Elect France, DRD Les REnardieres, F-77818 Moret Sur Loing, France
关键词
D O I
10.1063/1.1385160
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The presence of space charge in the polymeric insulation of high-voltage cables is thought to be correlated with electric breakdown. However, a direct link between molecular properties, space charge formation and eventual breakdown has still to be established. It is clear that both physical (e.g., conformational disorder) and chemical defects (e.g., broken bonds and impurities) are present in insulating materials and that both may trap electrons. We have shown that by defining the defect energy in terms of the molecular electron affinity, a relationship is established between the electron trap and the molecular properties of the material. In a recent paper [M. Meunier and N. Quirke, J. Chem. Phys. 113, 369 (2000)] we proposed methods that have made it possible to provide estimates of the energy, number and residence times of electrons in conformational traps in polyethylene. Typical physical trap energies are of the order of 0.15 eV and all are less than 0.3 eV. In the present paper we focus on the role of chemical defects, where we expect much deeper traps but at very low concentrations. Following the methodology used in our previous paper we have used density-functional theory to calculate trap energies for a set of chemical impurities and additives commonly found in polyethylene used for high-voltage cable insulation. In an extension of our approach we have estimated the effect of neighboring molecules on the trap energies of such defects. The resulting trap energy-trap density distribution reveals some very deep (>1 eV) traps presumably implicated in the formation of long-lived space charge in polymeric insulators and consequently to changes in the dielectric properties of the material. (C) 2001 American Institute of Physics.
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页码:2876 / 2881
页数:6
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