2018-Sustainable Industrial Processing Summit
SIPS2018
Volume 6. New and Advanced Materials and Technologies
| Editors: | F. Kongoli, F. Marquis, P. Chen, T. Prikhna, N. Chikhradze |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2018 |
| Pages: | 392 pages |
| ISBN: | 978-1-987820-92-8 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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The Quest for Electronic Ferroelectricity in Organic Charge-transfer Crystals
Alberto Girlando1;1PARMA UNIVERSITY, Parma, Italy;
Type of Paper: Regular
Id Paper: 108
Topic: 43
Abstract:
Organic ferroelectric materials that can operate at room temperature are in demand in the emerging field of lightweight and environmentally friendly electronics. In recent years, attention has focused on mixed stack charge-transfer (ms-CT) co-crystals, made up by planar pi-electron donor (D) and acceptor (A) molecules alternating along the stack direction. These materials are characterized by r, the degree of CT, ranging from 0 to 1, with r ~ 0.5 separating the neutral (N) from the ionic (I) ground state. Increase of the Madelung energy, following lattice contraction by lowering temperature, may induce a peculiar phase transition, the N to I one, with r crossing the N-I borderline. Ionic systems are subject to the Peierls instability, yielding to dimerization of the stack, hence potential ferroelectricity. Indeed, the prototypical ms-CT crystal Tetrathiafulvalene-Chloranil (TTF-CA) becomes ferroelectric in the low temperature (below 80K) I dimerized phase [1]. The TTF-CA ferrolectricity is electronic in nature, rather than ionic, being characterized by higher polarization and fast response to the electric field [2]. However, the search for other ms-CT crystals exhibiting electronic ferroelectricity at higher temperatures proved to be very challenging [3], since ionic or intermediate ionicity systems are relatively rare, and other conditions have to be met. In this paper, the quest for electronic ferroelectricity will be shortly reviewed. A strong electron donor, 3,3,5,5-Tetramethylbenzidine (TMB) has been coupled with a series of pi-electron molecules of increasing acceptor strength [4]. The co-crystal of TMB with Tetracyanoquinodimethane (TCNQ) undergoes a valence instability transition around 200 K, ending in the same ferroelectric structure as TTF-CA. Unfortunately, the ferroelectricity could not be directly tested, since the crystals are damaged at the transition. Other systems in the series are currently being investigated. Results on other ms-CT crystals with polar structure will be presented, even if they do not exhibit true ferroelectricity. The aim is to find the conditions which have to be met to obtain electronic ferroelectricity, so that suitable systems can be properly engineered.
Keywords:
New and advanced materials;References:
[1] K. Kobayashi, S. Horiuchi, R. Kumai, F. Kagawa, Y. Murakami and Y. Tokura, Phys. Rev. Lett. 108 (2012) 237601.[2] S. Horiuchi, K. Kobayashi, R. Kumai and S. Ishibashi, Chem. Lett. 43 (2014) 26-35.
[3] A. S. Tayi, et al., Nature 488 (2012) 485-489. G. Da'Avino et. al., Nature 547 (2017) E9.
[4] N. Castagnetti, M. Masino, C. Rizzoli, A. Girlando and C. Rovira, Phys. Rev. Mater. 2 (2018) 024602.