Synthesis and characterisation of materials with potential multiferroic behaviour

D'Souza, Rhys (2010). Synthesis and characterisation of materials with potential multiferroic behaviour. University of Birmingham. M.Res.

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Abstract

The ceramic method was used to produce Aurivillius phase materials, B i $_3$ NbTiO $_9$ and Bi $_4$ Ti $_3$ O $_1$ $_2$ . Unit cell structures have been determined to be of A2 $_1$ am and Fmmm symmetry, respectively. In addition, the fractional co-ordinates of the constituent atoms has been calculated by Rietveld refinement. A range of materials of general formula Bi $_5$ Fe $_1$ $_+$ $_x$ Ti $_3-x)\O\(_1$ $_5$ was produced with a value of x ranging from 0 to 2.5, which is higher than reported. Attempts to produce Bi $_5$ Fe $_4$ O $_1$ $_5$ , with all the Ti $^4$ + sites occupied by iron atoms proved unsuccessful. The space group of Bi $_5$ FeTi $_3$ O $_1$ $_5$ was determined to be A2 $_1$ am, however, the other 4-layer bismuth phases proved difficult to characterise without more data. Increasing the number of pseudo-perovskite layers from 2 to 3 to 4 (Bi $_3$ NbTiO $_9$ to Bi $_4$ Ti $_3$ O $_1$ $_2$ to Bi $_5$ FeTi $_3$ O $_1$ $_5$ ) had a notable effect in increasing the unit cell size along the z-axis, going from c=25.192(1)Å to c=32.785(1)Å to c = 41.179(1). The magnetic properties of Bi $_5$ FeTi $_3$ O $_1$ $_5$ , Bi $_5$ Fe $_2$ Ti $_2$ O $_1$ $_5$ and Bi $_5$ Fe $_3$ TiO $_1$ $_5$ have been recorded, as part of an attempt to find multiferroic materials. The information collected would suggest that Bi $_5$ FeTi $_3$ O $_1$ $_5$ and Bi $_5$ Fe $_3$ TiO $_1$ $_5$ display some anti-ferromagnetic behaviour, whereas Bi $_5$ Fe $_2$ Ti $_2$ O $_1$ $_5$ appears to be a paramagnet. Failure to produce Bi $_5$ MnTi $_3$ O $_1$ $_5$ , by other researchers methods, raises doubts about manganese substitution into the bismuth-layer structure.