X-ray diffraction studies on aluminum-substituted barium hexaferrite

Abstract

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 BaAl x Fe 12− x O 19 having x=2,4, 6, 8 and 10. The precursors were prepared by using stoichiometric amounts of Ba, Al and Fe 3+ nitrate solutions with urea as the precipitating agent. The hydrothermally prepared precursors were calcined at temperatures in the range of 800–1200 °C. 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 °C calcined samples showed any crystalline phase of Al. The 1200 °C calcined samples showed that Al-substituted 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. BaCO 3 was found be present even at 1200 °C in all the samples except for the one having Fe/Al ratio 5. The normal decomposition temperature of BaCO 3 is between 950 and 1050 °C. It is difficult to explain the increased stability of BaCO 3, which is perhaps responsible for hindering the formation of aluminum-substituted barium ferrite having Fe/Al ratio ≤2. The Al substitution in barium hexaferrite was confirmed through magnetic measurements.