Effect of internal brownian particles on phase transition of order-disorder crystalst

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Abstract
The behavior of the low frequency dielectric constants of NaNO2 as a function of frequency and temperature is explained by assuming a correct balance between the Lyddane-Sachs-Teller and Mason-Debye relaxation contributions to the dielectric constant. This new approach shows that in general whenever a sublattice of brownian particles exists in a crystal, the behavior of the activation energy ΔU as a function of temperature plays even a much more important role than has been considered up to now and that the fact that ΔU ≠ 0 at the transition temperature implies a hard core frequency contrary to the soft mode theory. Further implications of these ideas to dielectric and phase transition mechanisms are discussed.