First-principles investigation of the ferroelectric transition metal oxytetrahalides with atomically-thin domain wall

We investigate ferroelectric properties of quasi-one-dimensional MOX₄ (M = Cr, Mo, W, and X = F, Cl, Br) materials using first-principles density functional theory. The material consists of weakly coupled one-dimensional chains having a small energy difference between the polar and antipolar phases. The compositional dependence on the ferroelectric and piezoelectric properties such as switching polarization, energy barriers, Born effective charges, and piezoelectric coefficients are investigated. We find that most of the MOX₄ systems exhibit sizable polarization and large piezoelectric coefficients comparable to conventional ferroelectrics. More importantly, we find that the energy cost of forming a 180° domain wall is negligibly small due to the weak interchain coupling, having an atomically thin domain wall with almost no reduction in the local polarization. The robust ferroelectric switching, atomically thin ferroelectric domain wall, and large piezoelectric coefficients make the MOX₄ family of materials potential candidates for applications for efficient electronic devices such as high-density ferroelectric memories and high-resolution pressure sensors.