Fig. 1a and b show the XRD pattern of furnace cooled and
quenched Fe excess MgFe2O4 powder samples.The observed peaks
were matched with JCPDS card no73-1720 and 33-0664 for
MgFe2O4 and α-Fe2O3, respectively.
From Fig. 1a and b,it can be seen that the samples have formed
the magnesium ferrite phase.In addition to that a phase of
α-Fe2O3 is also seenforallsamples.Itisalsoseenthattherelative
intensity of(104)peakof α-Fe2O3 (highest intensitypeakof
α-Fe2O3) isnotthesameinallspectra.Theintensityof(104)peak
of α-Fe2O3 initially increaseswithcalcinationtemperature,witha
maximum observedforMgF600FC_5andMgF500QN_5andthen
decreases athighertemperatures.Thisindicatesthatsomeofthe
excessFeaddedtothesystemisprecipitatingas α-Fe2O3 phase for
all samples.Similarobservationhasbeenreportedbyother
workers [9].
Table1 givestheamountof α-Fe2O3 in allsamplesobtained
from Rietveldrefinement. Itcanbeseenfrom Table1 that, this
amount isnotsameinallthesamples.Theamountisgreaterthan
5 mol%,forsamplescalcinedandfurnacecooledorquenchedfrom
500and600 1C. ForsampleMgF800FC_5,theamountof α-Fe2O3
phase isonly0.2%.Theabilityofspinelstructuretoaccommodate
excessFeionshasbeenalreadyshownandthequantityofexcess
Fe ionsthatcanbeaccommodatedincreasesasafunctionof
calcination temperature