“STUDY OF THE MORIN TRANSITION IN PSEUDOCUBIC -Fe2O3 PARTICLES”

J,F. BENGOA; M.S. MORENO; S.G. MARCHETTI; R.E. VANDENBERGHE; RC. MERCADER

Mexico, DF

Conferencia; “Ninth Latin American Conference On Applications Of The Mössbauer Effect”; 2004

We have studied the Morin transition in nanostructured pseudocubic a-Fe2O3 particles of about 1.8 mm side. The preparation was carefully chosen to obtain a system with a very narrow crystallite size distribution and particles of homogeneous morphology. Two samples were studied: one without thermal treatment (a-Fe2O3(ap)) and another annealed at 673 K in air for 12h (a-Fe2O3(an)). Both were characterized by XRD, SEM, TGA and Mössbauer spectroscopy. The results indicate that the Morin transition is suppressed for a-Fe2O3(ap), however, a-Fe2O3(an) has a TM » 230 K and the transition is completed over a very narrow temperature range. These results are discussed in connection with the crystallite size, the cell parameters, and the presence of OH- groups (hydrohematite) or incorporated water (protohematite).