Préparation et Determination Structurale de la Forme Haute Temperature de KH2PO4

Crystals of the high-temperature form of potassium dihydrogen phosphate (KH2PO4(KDP)) have been prepared by a hydrothermal method. The old parameters and space group are rectified and the structure is solved for the first time. It crystallizes in the monoclinic system, space groupP21/c(No. 14),a=7.4514(7) Å,b=14.5582(9) Å,c=9.366(7) Å, andβ=127.65(1)°, andZ=8. The structure is refined toR=0.032 for 1530 independent reflections and compared with the other KDP forms. The distribution of hydrogen atoms over PO4tetrahedra and the structural relationship with the various forms of KDP are discussed. The doubling of thebparameter is related to structural features.