Berlin 2018 – wissenschaftliches Programm

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 2: Ferroelectric Domain Walls I (joint session KFM/TT)

KFM 2.4: Vortrag

Montag, 12. März 2018, 10:30–10:45, EMH 225

Anomalous domain wall motion in Cu-Cl boracite: negative permittivity in an improper ferroelectric? — •Charlotte Cochard¹, Joseph G.M. Guy¹, Michael P. Campbell¹, Roger W. Whatmore², Amit Kumar¹, Raymond G.P. McQuaid¹, and Marty Gregg¹ — ¹Queen’s University Belfast, Belfast UK — ²Imperial College London, London, UK

Negative capacitance has attracted a lot of attention recently thanks to its potential to enable shorter switching time of transistors. It has been observed in systems as diverse as p-n junction, electrochemical systems, and ferroelectrics. To date, no single-phase material has been reported to exhibit negative capacitance.

In this work, we show that regions in a boracite crystal (Cu₃B₇O₁₃Cl) exhibit anomalous electric-field-induced movement of charged domain walls, consistent with negative permittivity. Boracites naturally display domain wall configurations, seen to be electrically active by current mapping [1]. While applying an electric field across some of these charged walls, we observed that domains with polarisation components pointing opposite to the electric field grow at the expense of domains with polarisation components aligned with the field. Thus dP/dE is negative and hence permittivity is negative. This behaviour is proposed to originate from the improper ferroelectric nature of the boracite: the elastic energy payoff, due to polarisation-strain coupling, is greater than the work done in generating increased polarisation against the applied electric field.

[1] R.G.P. McQuaid, et al. Nat. Commun. 8, 15105 (2017).