Ferroelectric Phase Transition in Ammonium Hydrogen Bis (Chloroacetate) : I. Nuclear Quadrupole Resonance in NH_4H(ClCH_2COO)_2 and ND_4D(ClCH_2COO)_2

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Temperature dependence of the ^35Cl nuclear quadrupole resonance in NH_4H(ClCH_2CO_2)_2 and ND_4D(ClCH_2CO_2)_2 showed that there was a single line above 120K and 130K, respectively. Below these transition temperatures the spectrum consists of a pair of lines whose separation gradually increases at lower temperatures, being 2.17 times as large in the D salt as in the H salt. The resonance frequencies at 20.1K were 35.1230 and 35.3680MHz in the H salt and 35.034 adn 35.566MHz in the D salt. Infrared absorption spectra also showed splitting in the C-Cl stretching band below the transition temperature. Principal values of the electric field gradient tensors at chlorine sites were determined for the two phases of the H salt; the direction of the principal Z axes being to change to change asymmetrically as the transition point is traversed downwards. Two possible mechanisme, the continuous displacive transition and the order-disorder transition, were examined and shown to account equally well for the experimental results.
社団法人日本物理学会の論文
1973-11-05