Large Vertical Piezoelectricity in a Janus Cr(2)I(3)F(3) Monolayer

Two-dimensional (2D) materials have potential applications in nanoscale sensors and spintronic devices. Herein, motivated by experimental synthesis of a CrI [Formula: see text] monolayer possessing intrinsic magnetism and a Janus MoSSe monolayer with piezoelectricity, we propose a 2D Janus Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer as a multifunctional material exhibiting both piezoelectricity and ferromagnetism. Using density functional theory calculations, we systematically investigated the structural stability and the electronic, magnetic, and piezoelectric properties of the Janus Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer. We predicted that a vertical polarization of up to −0.155 × 10 [Formula: see text] C/m is induced in the Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer due to the breaking of symmetry. The origination mechanism of polarization was demonstrated in terms of a local dipole moment calculated by maximally localized Wannier functions. Meanwhile, it was found that a remarkable piezoelectric response can be produced under a uniaxial strain in the basal plane. The calculated piezoelectric coefficients of the Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer compare favorably with those of the frequently used bulk piezoelectric materials such as [Formula: see text] –quartz and wurtzite AlN. Particularly, the e [Formula: see text] and d [Formula: see text] values of the Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer are nearly 10 times as large as that of Mo-based transition metal dichalcogenides. We also found that the magnitude of e [Formula: see text] mainly arises from the ionic contribution, while the electronic contribution can be nearly neglected. The considerable piezoelectric response combined with the intrinsic magnetism make the Janus Cr [Formula: see text] I [Formula: see text] F [Formula: see text] monolayer a potential candidate for novel multifunctional devices integrating both piezoelectric and spintronic applications.