Multiscale lattice and bonding dynamics in high-entropy ferroelectrics

Ferroelectric high-entropy ceramics (HECs) have recently gained significant attentions in advancing high-performance energy storage and dielectric capacitors applications. A critical challenge is to understand the atomic-scale origin of their distinct macroscopic functionalities because HECs always have disordered atomic arrangements and complex lattice distortions. Here, through a combination of polarized Raman spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and crystal orbital Hamilton population (COHP) calculations, we establish the routine to identify the multiscale physical process between phonon-bonding dynamics and lattice polarization responses in a HECs system, namely, $({\mathrm{Sr}}_{0.2}{\mathrm{Ba}}_{0.2}{\mathrm{Pb}}_{0.2}{\mathrm{La}}_{0.2}{\mathrm{Na}}_{0.2}){\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$. We find that the off-centering Nb ions contribute to octahedral tilting. Specifically, the bending modes restrict O-Nb-O bond-angle distortions, strengthening the $ab$-plane covalent network to enhance breakdown fields. The rigid stretching mode suppresses oxygen displacement, thus stabilizing polar order. The constrained Nb vibration synergistically boosts maximum polarization via Nb-O bond stiffening and reduces remnant polarization. The COHP model theoretically compliments the experimental results. This work deciphers the multiscale interplay of structure-functionality relationship in HECs, offering a universal strategy to tailor high-entropy materials by multiscale analysis of phonon dynamics and bonding characteristics.