Effect of phase transition on the dielectric properties of thin organic layers

Abstract

Working with capacitors produced with thin organic layers (orthophenanthroline with three stearic chains) significant variations were observed in parallel conductance and capacitance in the neighborhood of the transition point T=35 °C. An investigation of conductance properties in alternating current revealed that these layers are the site of ion relaxation phenomena between two equilibrium positions separated by a potential barrier. A sudden drop in activation energy was observed at 35 °C, falling from a value E1=1.25 eV to E2=0.65 eV. This variation, attributed to a phase change, leads to a rapid increase in capacitance and conductance G in the neighborhood of 35 °C (ΔG/G≳50%/d °C). The phenomenon is reversible, and the structure oscillates between two stable states, depending on temperature.