X-ray diffraction studies on aluminum-substituted barium hexaferrite

Effect of aluminum substitution in barium hexaferrite was studied following the hydrothermal precipitation–calcination techniques. It was
attempted to prepare aluminum-substituted barium hexaferrites with compositions BaAlxFe12 xO19 having x = 2,4, 6, 8 and 10. The
precursors were prepared by using stoichiometric amounts of Ba, Al and Fe3 + nitrate solutions with urea as the precipitating agent. The
hydrothermally prepared precursors were calcined at temperatures in the range of 800–1200 jC. The detailed work carried out on
identification of crystalline phases through XRD revealed that, after the hydrothermal treatment, the samples showed barium carbonate,
hematite and boehmite as the crystalline phases (except that boehmite was not identified for Ba/Al/Fe ratio as 1:2:10). Irrespective of the Al
content, none of the 1000 and 1200 jC calcined samples showed any crystalline phase of Al. The 1200 jC calcined samples showed that Alsubstituted
barium hexaferrite is formed only with the Ba/Al/Fe atomic ratio of 1:2:10. With increase in the Al content, formation of
hexaferrite was not observed. BaCO3 was found be present even at 1200 jC in all the samples except for the one having Fe/Al ratio 5. The
normal decomposition temperature of BaCO3 is between 950 and 1050 jC. It is difficult to explain the increased stability of BaCO3, which is
perhaps responsible for hindering the formation of aluminum-substituted barium ferrite having Fe/Al ratio V2. The Al substitution in barium
hexaferrite was confirmed through magnetic measurements.