Investigations into the nature of spontelectrics: nitrous oxide diluted in xenon

Abstract

The recent discovery of a new class of solids displaying bulk spontaneous electric fields as high as 10⁸ V m⁻¹, so-called ‘spontelectrics’, poses fundamental and unresolved problems in solid state physics. The purpose of the present work is to delve more deeply into the nature of the interactions which give rise to the spontelectric effect in films of nitrous oxide (N₂O), by observing the variation of the spontaneous field as the N₂O molecules are physically removed from one another by dilution in Xe. Data, obtained using the ASTRID storage ring, are presented for films diluted by factors ξ = Xe/N₂O of 0.9 to 67, at deposition temperatures of 38 K, 44 K and 48 K, where films are laid down by deposition from a gas mixture. Results show that the spontelectric field decreases as ξ increases and that at ξ = 67 for 44 K deposition, the spontelectric effect is absent. Reflection–absorption infrared spectroscopy (RAIRS) data are also reported, providing insight into the structure of Xe/N₂O films and specifically showing that N₂O remains dispersed in the Xe/N₂O films prepared here. A simplified theoretical model is developed which illustrates that electric fields can be understood in terms of dilution-dependent dipole orientation. This model is used to reproduce experimental data up to an average molecular separation, s, of ≥1.25 nm apart, ∼4 times that associated with pure solid N₂O. The disappearance of the spontelectric effect at larger average distances of separation, between s = 1.25 nm and s = 1.75 nm, is a phenomenon which cannot be described by any existing model but which shows that dipole–dipole interactions are an essential ingredient for the creation of the spontelectric state.