Crystal structure and phase transition at low temperature in betaine phosphate

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