Enhanced bulk modulus and reduced transition pressure in gamma-Fe2O3 nanocrystals

Synchrotron radiation X-ray diffraction studies of gamma-Fe2O3 have been pe rformed with emphasis on the pressure-induced phase transformation gamma(ma ghemite) --> alpha(hematite) and the equation of state of the nanophase mat erial. For gamma-Fe2O3 the bulk modulus has been found to increase from 203 GPa for the bulk material to 305 GPa for 9 nm size crystals. At the same t ime the transition pressure decreases from 35 to 27 GPa. The reduced transi tion pressure is explained in terms of nucleation and growth, the larger vo lume change upon transition in the nanocrystalline material being the main factor.