Indexed on: 16 May '21Published on: 10 May '21Published in: Applied physics letters
Applied Physics Letters, Volume 118, Issue 19, May 2021. The hydrogen-bonded molecular ferroelectric crystal triglycine sulfate (TGS) is used for the study of polarization reversal features in the structure of mixed ionic–electronic conductor-on-ferroelectric type. The dynamic current–voltage (I–V) loops of thin TGS plates of polar (010) cut are investigated. The plates were covered with dissimilar electrodes on the opposite surfaces, vacuum-deposited Ag, and Ag-paste diluted with a water–ethanol mixture. After electroforming in the low-voltage vicinity of coercive voltage, a reversible transformation of the I–V loop shape occurs during further cycling: the loops' shape changes from the shape typical for nonlinear dielectrics to the one typical for memristive systems, and then to the shape typical for ferroelectrics (and vice versa) with a sequential increase (decrease) of drawing voltage amplitude. Such “awakening” and “falling asleep” of the memristor type I–V loops is apparently associated with a reversible electromigration and accumulation of charged species (e.g., protons), in the hydrated surface layer of TGS, as a component of electrochemical capacitor-on-ferroelectric structure. The observed transformation can be explained by considering the coupled ion transfer and polarization reversal under the applied voltage, when the swinging of the boundary of the built-in chemical inhomogeneity under conditions of linear and/or nonlinear dynamics of ion drift and ionic concentration polarization caused by charged species transfer take place. The revealed metamorphosis of I–V-loops provides insight into the functional possibilities of ferroelectric materials for the future development of memristive devices with a wide variety of applications.