Enhanced polarization in epitaxially strained monoclinic potassium niobate for lead-free electromechanical applications

Abstract

To further our understanding of how complex anisotropic structure-property relationships may be rationalized by their local atomic arrangements in ferroelectric materials, using the newly-found metastable monoclinic P m phase of...

Using Feature‐Assisted Machine Learning Algorithms to Boost Polarity in Lead‐Free Multicomponent Niobate Alloys for High‐Performance Ferroelectrics

“…It has been previously shown that for the pristine KNO system, K contributes minimally to the total P s while the major contribution comes from the NbO 6 octahedrons. [ 39,40 ] This suppression of the polarization response of K reflects the strong ionic interactions between K and O ions. [ 39 ]…”

“…As evident from Figure 2, although the contribution of NbO 6 octahedrons to P s is dominant and well‐understood (i.e., via intra‐octahedral tilting mechanism), [ 39,40,46 ] the preferred use of $$\widehat{P}$$ is palpable for the enhanced P s in for example, K 1 − x Li x NbO 3 alloys.…”

“…This leads to further Nb off‐centering distortions via a second‐order Jahn–Teller effect [ 36 ] as identified by the recently proposed anisotropic bond elongation index (Figure S5 , Supporting Information). [ 40 ] To sum things up, steric effects (from the varying sizes of cations at the A‐site) can be used to enhance polar distortions in both the A‐ and B‐site cations. These results offer an additional engineering rule of tuning the A‐site occupancy via alloying in addition to the known intra‐octahedral distortions in perovskites.…”

“…For the DFT exchange‐correlation ( xc ) functional, it had been reported in a previous work [ 40 ] that the Perdew–Burke–Ernzerhof xc functional revised for solids (PBEsol) [ 58 ] provided the best agreement with the experimental lattice parameters of KNbO 3 polymorphs. Brillouin zone integrations were sampled with a Γ‐centered k ‐point mesh of 8 × 8 × 8 for the primitive unit cell of tetragonal and orthorhombic phases, and for larger supercells used in this work, the k ‐point meshes were then equivalently folded.…”

“…It has been previously shown that for the pristine KNO system, K contributes minimally to the total P s while the major contribution comes from the NbO 6 octahedrons. [39,40] This suppression of the polarization response of K reflects the strong ionic interactions between K and O ions. [39] In Figure 2, we plot the total and partial P s (due to the A-site cations and the NbO 6 octahedrons) for the KNO-based alloys in the tetragonal (upper panels) and the orthorhombic (lower panels) phases.…”