Crystal Structure and Phase Transition at Low Temperature in Betaine Phosphate

The low temperature phase of betaine phosphate was investigated by X-ray diffraction. The intensity of the X-ray diffraction at 20 K was measured and analyzed to determine the crystal structure. The least-squares method converged at the R factor 4.6% with 3349 reflections (4.2% for 2081 normal reflections and 8.4% for 1268 superlattice reflections). The structure analysis clarified that the protons (the hydrogen atoms of the phosphate origin) between neighboring phosphate tetrahedrons were in order in the low temperature phase causing the super structure of cell-doubling. The temperature dependence of superlattice reflections was measured and a kink was found corresponding to the intermediate phase between 76 K and 85 K