CRYSTAL-GROWTH, ROOM-TEMPERATURE CRYSTAL-STRUCTURE AND PHASE-TRANSITIONS OF KMNPO4

Single crystals of KMnPO4 grown in a KCl flux show ferroelastic domains, The structure was determined on an optically controlled single domain crystal by X-ray diffraction methods. The cell is triclinic with dimensions a = 5.4813(5), b = 8.627(1), c = 8.887(1), in Angstrom, alpha = 87.73(1)degrees, beta = 89.10(1)degrees, gamma = 88.01(1)degrees, V-M = 419.6(1) Angstrom(3) and Z = 4. The structure is closely related to the stuffed beta-tridymite type. DTA experiments between room temperature and 1000 degrees C and polarized light microscopy observations showed four phase transitions: at 165, 330, 353 and 707 degrees C.