MICROSTRUCTURAL AND MAGNETIC STUDIES ON HYDROTHERMALLY PREPARED HEMATITE

Hematite particles of various shapes and sizes have been prepared hydr othermally at different pH values ranging from 3 to 10 from ferric chl oride solution at 180 degrees C. Particle size decreases with an incre ase in the pH of precipitation as observed from Transmission Electron Micrographs (TEM). A comparison of TEM and mean crystallite diameter ( MCD) from XRD data reveals that the particles prepared are polycrystal line in nature. The polycrystallinity decreases with an increase in th e pH of precipitation, and at pH 10 almost single crystalline nature o f particles is obtained. Polycrystalline monodispersed pseudocubic par ticles obtained at pH 3 exhibit very high coercive force and remanent magnetization which decreases with an increase in pH, whereas Morin tr ansition temperature, T-m, shows an opposite trend. Magnetic a.c. susc eptibility increases with an increase in pH up to pH 7 and then decrea ses. A probable mechanism for the formation of polycrystalline particl es has been suggested in order to explain the above trends in magnetic behavior. (C) 1997 Academic Press