Dynamics of Displacive-Type Ferroelectrics : Soft Modes

概要

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Dynamical behaviors of the soft mode in displacive-type ferroelectrics such as SrTiO_3 and BaTiO_3 are studied theoretically. (1) It is pointed out from the irreversible thermodynamical view point that the critical slowing-down appears directly through frequency, and not directly through damping as in order-disorder phenomena and in magnetic systems. (2) The well-known Lyddane-Sachs-Teller and Cochran-Kurosawa relations for the uniform mode are generalized on the quantum-statistical basis to Ω_k=√<e^2/MX_k>, where Ω_k is the frequency of the soft mode with wave vector K, e the effective charge on an ion, M the reduced mass of positive and negative ions, X_k the wave length dependent electric susceptibility. (3) The damping constant Γ_k is calculated explicitly, whereby the neutron experiments in SrTiO_3, KTaO_3 and BaTiO_3 due to Cowley, and Shirane et al. are explained. (4) An anomalous increase in Γ_k near the paraelectric Curie point is predicted together with a characteristic behavior of SrTiO_3 from others.
社団法人日本物理学会の論文
1969-01-05