Neutron-diffraction study of K(H 1-x D x ) 2 PO 4

The crystal structure and phase transition of K(H1-xDx)2PO4 were studied by single-crystal and powder diffractometers at the HANARO reactor. The single crystals were grown from D2O with reagent KH2PO4. The crystal is tetragonal at room temperature with lattice parameters of a=7.4633(7) A, c=6.9785(5) A and Z=4 and its structure was refined to final R and wR values of 0.041 and 0.096, respectively. A disordered distribution of D and H atoms was observed at room temperature. On cooling, a tetragonal to orthorhombic phase transition is observed. The transition temperature Tc=193 K is obtained for the sample K(H0.34D0.66)2PO4. The result of the neutron-diffraction method is in good agreement with the result of the differential scanning calorimetry measurement.