Ab-initio study of ferroelectricity and piezoelectricity in quasi-one-dimensional transition metal oxyhalides

Ferroelectrics (FE’s) with atomically thin domain walls are actively investigated due to the potential applications in high-density non-volatile memory devices. Especially, the quasi-one-dimensional dielectrics are considered as a viable candidate from the large anisotropy in the FE coupling. We investigate a family of transition metal oxyhalides, MOX₄ (M = Cr, Mo, and W; X= F, Cl, and Br) consisting of weakly coupled one-dimensional chains. First-principles density functional theory calculations are performed to explore the FE and piezoelectric properties in these MOX₄ systems. The polarization, energy barriers, and piezoelectric coefficients are systematically investigated. We find that the majority of the MOX₄ systems exhibits robust FE switching with sizeable polarization that is comparable with those of conventional bulk FE materials. Moreover, we calculate the domain structure of the MOX₄ systems and find an atomically thin domain wall with negligible reduction in the polarization. The robust FE switching and the ultrathin FE barriers between the quasi-one-dimensional chains make them potential candidates for applications in high-density FE memories.