Synthesis and characterisation of materials with potential multiferroic behaviour

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