Abstract
We use a combination of in-situ neutron reflectometry (NR) measurements, IR spectroscopy and temperature programmed desorption (TPD) experiments to demonstrate that films of nitrous oxide and undergo a temperature controlled phase transition to a crystalline phase at 48 K. We show that the spontelectric model yields two distinct sets of parameters, describing two different polarised phases of solid N2O which correspond to the two observed structural phases. The spontelectric model invokes long-range ordering of molecular dipoles throughout the solid to explain the formation of the macroscopic polarisation.[14] There is no equivalent description of such non-local, non-linear ordering forces in contemporary descriptions of molecular solids.
What is most remarkable is that films grown in the low temperature phase regime, below 48 K, maintain the same degree of polarisation, vis-a-vis dipole orientation, when annealed across the phase boundary to the high temperature phase regime. This behaviour, in combination with spontaneous macroscopic polarisation which results from long range dipole orientation, set the spontelectric class of materials apart from other polarised solid phases.
