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 Pca2(1) 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. Published under an exclusive license by AIP Publishing.