Degree of Order by X-Ray Crystal Structure Analysis in Triglycine Sulfate

Temperature dependence of the degree of order in triglycine sulfate has been investigated by the X-ray crystal structure analysis where the averaged structure is assumed to consist of parallel dipoles and anti-parallel dipoles. Contrary to the degree of order estimated by the spontaneous polarization, the degree of order by the X-ray crystal structure analysis does not vanish even in the paraelectric phase. Since coherence length of X-ray is shorter than the sample size, the observed averaged structure looks like the structure in the ferroelectric phase even in the paraelectric phase when correlation length of interaction among the dipoles is longer than the coherence length of X-ray. The degree of order by the X-ray crystal structure analysis reflects not only the long-range order but also correlations among the dipoles.