Further insights into polarization switching phenomena of CuInP₂S₆ and CuInP₂Se₆ single crystals

In addition to graphene and graphite, some of the best known layered materials are the layered thiophosphates with common chemical composition of CuInP₂Q₆ (Q=S, Se). A comprehensive study of polarization swithing in a ferroelectric copper indium thiophosphate CuInP₂S₆ (CIPS) has been reported both in nanoscale as well as bulk crystals [1], [2]. It was confirmed stable ferroelectric polarization in an intrinsically layered CIPS (below ~50 nm thickness). Anomalous polarization switching was found in a ferroelectric CIPS in bulk crystalline. Such anomalous behaviour were found to correlate with its ionic conductivity. The sulfur and selenium compounds have similar structure. Despite this structural similarity, the physical properties are quite different as evidenced by dielectric, ultrasonic, caloric etc. characterization [3]. It was proposed that this anomaly is evidenced for the coexistence of ferrielectric and antiferroelectric ordering [4]. In this report, swithing dynamics of CuInP2Se6 single crystals are presented over wide ranges of temperature and electric field.

The single crystals CuInP₂Se₆ were grown from gas phase by chemical transport reactions. Ferroelectric swithing is usually dificult to experimentally demonstrate in these materials, mostly due to an intrinsic high conductivity and low-temperature ferroelectric behaviour. Through comprehensive polarization switching and dielectric spectroscopy studies in both temperature and frequency domains, we reveal that the ionic conductivity influences polarization swithing behavior by thermally activated hopping of copper ions in the lattice of CuInP₂Se₆.

References

[1] A. Belianinov et al., “CuInP₂S₆ Room Temperature Layered Ferroelectric,” Nano Lett., vol. 15, no. 6, pp. 3808–3814, 2015.

[2] S. Zhou et al., “Anomalous polarization switching and permanent retention in a ferroelectric ionic conductor,” Mater. Horizons, vol. 7, no. 1, pp. 263–274, 2020.

[3] S. Zhou, L. You, H. Zhou, Y. Pu, Z. Gui, and J. Wang, “Van der Waals layered ferroelectric CuInP₂S₆: Physical properties and device applications,” Front. Phys., vol. 16, no. 1, pp. 13301-1–30, 2021.

[4] A. Dziaugys et al., “Piezoelectric domain walls in van der Waals antiferroelectric CuInP₂Se₆,” Nat. Commun., vol. 11, no. 1, pp. 1–7, 2020.