STRUCTURAL AND MAGNETIC-PROPERTIES OF THE BROWNMILLERITE CA2ALXFE2-XO5 SYSTEM

A series of solid solutions in the Ca2AlFe2-xO5 (x=0.00 0.50, 0.66, 1. 00 and 1.34) system with brownmillerite structure has been synthesized at 1100 degrees C under an atmospheric air pressure. The solid soluti ons are analysed by powder x-ray diffraction analysis, Mohr salt titra tion, thermal analysis, and Mossbauer spectroscopic analysis. The x-ra y diffraction analysis assigns the compositions of x=0.00 and 0.50 to the space group Pcmn and those of x=0.66 1.00, and 1.34 to the Ibm2. M ossbauer spectra have shown the coordination state and disordering of Al3+ and Fe3+ ions. The substituting preference of Al3+ ions for the t etrahedral site decreases with increasing x value. Magnetic susceptibi lity of the system has been measured in the temperature range of 5 K t o 900 K. The solid solutions of the compositions of x=0.00, 0.50 and 0 .66 have shown a thermal hysteresis and the thermoremanent magnetizati on gap decreases with increasing x value in the above systems. However the compositions of x=1.00 and 1.34 do not show the hysteresis. The e xchange integral is calculated from Fe3+ ion occupancy ratio. The inte gral decreases with x value and thus the magnetic transition temperatu re decreases with the increasing x value.