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.

Automated summary

This study investigates the polarization switching pathways of orthorhombic HfO2 through first-principles calculations, revealing the importance of interface termination in determining the existence of two switching pathways and showing that the SA pathway has higher critical values. The application of lattice strains can induce a ferroelectric-paraelectric phase transition, but the trends of P-s and E-b under the same lattice strains vary depending on the switching pathways. However, strain engineering can efficiently improve E-b and P-s for both pathways in o-HfO2 films by carefully designing interfacial tail atoms.