The symmetry-mode decomposition for better understanding of the structural evolution presented in polar functional materials

Reference Presenter Authors
08-077 Yun Liu Liu, Y.(The Australian National University); The phase and structure evolution of the (1-x)AgNbO3-xLiTaO3 solid solution is investigated by the neutron diffraction, dielectric and ferroelectric measurements. The symmetry-mode decomposition of the distorted AgNbO3 structure defined on the experimental space group, Pmc21 has been conducted. The four main modes, T4+, H2, ?3 and ?4-, exhibit large distorted amplitude to stabilize the Pmc21 structure. The mode refinement with referring to the Pmc21 was adopted to (1-x)AgNbO3-xLiTaO3 material system. It is found that with the increasing LiTaO3 concentration, the orthorhombic phase partially transfers to the rhombohedral R3c phase and the fraction of the R3c phase gradually increases. Correspondingly, the mode amplitudes of the H2 and ?3 drop abruptly. The hidden structural correlation between H2 and ?3 modes facilitates the understanding of the antiferroelectric nature observed in the AgNbO3. The variation of the main modes rationally bridges the Pmc21 and R3c phases, revealing the underlying phase transition mechanism of these two phases. Additionally, the evolution of the R3c phase fraction and corresponded mode amplitude in both Pmc21 and R3c phases provides a clear picture to explain the additional peak observed in the temperature-dependent dielectric spectra and composition-dependent polarisation-electric field hysteresis loops.
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