Polarization- and stress-related lattice dynamics in solid-solution perovskite ferroelectrics

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Perovskite ferroelectrics play an essential role in modern science and technology. The excellent properties of perovskites are closely related to their lattice dynamics. Potassium tantalate niobate (KTa1-xNbxO3, abbreviated as KTN) is a typical solid-solution perovskite with superior properties. Although the optical and electrical performances of KTN crystals have been widely explored, information on their lattice dynamics is still scarce, which partially limits the research and performance optimization of KTN. As a solid-solution, spontaneous polarization of KTN exhibits strong tunability, and there is stress within KTN. Here, we performed first-principles calculations in conjunction with experiments to investigate the polarization- and stress-related lattice dynamics in KTN. We assigned the vibration modes of observed Raman peaks, and established the relationship between spontaneous polarization and vibration. Especially, the lattice dynamics evolution of KTN crystal under stress was investigated. And the results provide insights into the regulatory effect of stress on dielectric property from the perspective of lattice dynamics. Finally, the variation trends of phonons under stress, as well as the mechanism of stress effect in tetragonal perovskites were explained. The conclusions drawn for KTN crystal were generalized to tetragonal ferroelectric systems. Our results help to reflect spontaneous polarization and structural characteristics distribution through non-destructive Raman spectra, and give a reference for improving performance by regulating lattice dynamics. The findings will hopefully guide research on performance origin and refined design of perovskite functional materials.