Spontaneous electric fields in films of CF3Cl, CF2Cl2 and CFCl3

Abstract

Data are presented showing the spontaneous formation of electric fields within solid films of the chlorofluorocarbons (CFCs) CF₃Cl, CF₂Cl₂ and CFCl₃ as a function of film deposition temperature from 40 K and above. Electric fields, which arise through dipole alignment and lie in the range of a few times 10⁷ V m⁻¹ to a few times 10⁶ V m⁻¹, decrease as the degree of chlorination increases. Maximum deposition temperatures for display of an electric field lie at ∼50 K, ∼65 K and ∼52 K for CF₃Cl, CF₂Cl₂ and CFCl₃ respectively. CFCl₃ films possess electric fields which show an onset of temporal metastability between deposition temperatures of 46 K and 50 K. CF₃Cl and CF₂Cl₂ demonstrate temperatures of ∼65 K and ∼80 K at which the electric field in the film is removed by heating, so-called Curie points, with decay of the field spread over more than 10 K. CFCl₃ displays a comparatively sharp Curie point at 55 K. This variety of behaviour arises despite the resemblance of these three species in terms of electronic structure and gas phase dipole moment, emphasising the requirement for detailed chemical models of this phenomenon.