Switching pathway-dependent strain-effects on the ferroelectric properties and structural deformations in orthorhombic HfO2.

The polarization switching pathway plays a key role in deciding the magnitudes of the spontaneous polarization and the coercive electric field, which can be used to realize controllable ferroelectric properties. In this paper, by first-principles calculations, we reveal how the spontaneous polarization (P_s) and the switching barrier (E_b) of orthorhombic HfO₂ (o-HfO₂) respond to various lattice strains depending on two kinds of switching pathways, i.e., the shift-across (SA) pathway and the shift-inside pathway. It is revealed that the existence of the two pathways is most likely dependent on the interface termination of o-HfO₂, and the SA pathway exhibits higher critical values of both P_s and E_b. By applying lattice strains on o-HfO₂ (001) and (010) planes, a ferroelectric–paraelectric phase transition from the polar Pca2₁ to the nonpolar Pbcn can be observed. Importantly, the variation trends of P_s and E_b under the same lattice strains are found to be highly different depending on the switching pathways. However, by carefully designing the interfacial tail atoms, strain engineering can efficiently improve E_b and P_s for both pathways in o-HfO₂ films. Our work uncovers the mechanisms of the switching pathways and opens a new avenue for preparing high-performance ferroelectric devices using strain engineering. [ABSTRACT FROM AUTHOR]