Intriguing relaxor ferroelectricity in a polar CT crystal at the neutral-ionic interface

Abstract

We investigated the mixed-stack charge-transfer crystal, N,N'-dimethylphenazine-TCNQ (M${}_2$P-TCNQ), which is polar at room temperature and just at the neutral-to-ionic interface (ionicity $\rho \approx 0.5$). We detect the typical dielectric signature of a relaxor ferroelectric and an asymmetric positive-up-negative-down behavior. While relaxor ferroelectricity is usually ascribed to disorder in the crystal, we find no evidence for structural disorder in the investigated crystals. To elucidate the origin of M${}_2$P-TCNQ's dielectric properties we perform parallel structural and spectroscopic measurements, associated with theoretical modeling and quantum-mechanical calculations. Our combined effort points to a highly polarizable electronic system that is strongly coupled to lattice vibrations. The found indications for polarization reversal imply flipping of the bent conformation of the M${}_2$P molecule with an associated energy barrier of a few tens of an eV, broadly consistent with an Arrhenius fit of the dielectric relaxation times. While the polarization is mostly of electronic origin, its possible reversal implies slow collective motions that are affected by solid-state intermolecular interactions.

arXiv comment13 pages, 12 figures

References in corpus (12)

• Colossal dielectric constants in transition-metal oxides
• Multiferroicity due to charge ordering
• The ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors
• Anomalous dielectric response in the dimer Mott insulator $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$
• Evidence for multiferroicity in TTF-CA organic molecular crystals
• Relaxor ferroelectricity induced by electron correlations in a molecular dimer Mott insulator
• Evidence for electronically-driven ferroelectricity in the family of strongly correlated dimerized BEDT-TTF molecular conductors
• Dielectric Spectroscopy on Organic Charge-Transfer Salts
• Ferroelectric properties of charge-ordered alpha-(BEDT-TTF)2I3
• Tuning the magnetic dimensionality by charge ordering in the molecular TMTTF salts
• Slowing down of the relaxational dynamics at the ferroelectric phase transition in one-dimensional (TMTTF)2AsF6
• Correlation-driven electronic multiferroicity in (TMTTF)${}_2$-$X$ organic crystals

Cited by in corpus (1)

• Tetramethylbenzidine-TetrafluoroTCNQ: A narrow-gap semiconducting salt with room temperature relaxor ferroelectric behavior