Computational Discovery and Investigation of New Two Dimensional Ferroelectric Materials

Two dimensional ferroelectrics (2DFE, monolayer thick materials with a switchable spontaneous electric polarization) have been proposed for ultrathin electronic devices. However, 2DFEs with large out-of-plane polarizations, ideal for such applications, are challenging to find. Recently, Chandrasekaran et al. proposed that the functionalized MXene Sc₂CO₂ has a metastable state with an out-of-plane electric polarization larger than other common 2DFEs. [1] In this work, we used density functional theory (DFT) calculations to investigate additional M₂CX₂ materials (M = Sc, Y, La and X = O, F). We found that (1) chemical substitution of Sc with Y and/or O with F can preferentially stabilize the ferroelectric phase as the ground state; (2) such substitution can also be used to tune the polarization and band gap; and (3) these monolayers display large piezoelectric coefficients. We demonstrate how these properties can be continuously tuned by the application of external strain or by alloying to create Sc_2x­Y_2(1-x)CO₂ monolayers. Furthermore, we show that the surface reactivity of these materials can be controlled by switching the polarization and preferentially adsorb different adsorbates. Finally, we extend this to new families by using a high throughput DFT approach to scan through a database of 2D materials and compute their polarization to find and verify new 2D ferroelectric materials with out-of-plane polarizations.

 

[1] A. Chandrasekaran, A. Mishra, A. K. Singh, Nano Letters 17 3290 (2017)