Palizdar, Meghdad, Comyn, Tim P., Ward, Mike B., Brown, Andrew P., Harington, John, Kulkarni, Santosh, Keeney, Lynette, Roy, Saibal, Pemble, Martyn, Whatmore, Roger, Quinne, Christopher, Kilcoyne, Susan H. and Bell, Andrew J. (2011) Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics. In: Applications of Ferroelectrics (ISAF/PFM), 2011 International Symposium on and 2011 International Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, 24-27 July 2011, Vancouver, BC.

Oxide materials which exhibit both ferroelectricity
and ferromagnetism are of great interest for sensors and memory
applications. Layered bismuth titanates with an Aurivillius
structure, (BiFeO3)nBi4Ti3O12, can possess ferroelectric and
ferromagnetic order parameters simultaneously. It has recently
been demonstrated that one such example,
Bi5Fe0.5Co0.5Ti3O15,where n = 1 with half the Fe3+ sites substituted
by Co3+ ions, exhibits both ferroelectric and ferromagnetic
properties at room temperature. Here we report the fabrication
of highly-oriented polycrystalline ceramics of this material,
prepared via molten salt synthesis and uniaxial pressing of high
aspect ratio platelets. Electron backscatter images showed that
there is a secondary phase within the ceramic matrix which is
rich in cobalt and iron, hence this secondary phase could
contribute in the main phase ferromagnetic property. The
concentration of the secondary phase obtained from secondary
electron microscopy is estimated at less than 2.5 %, below the
detection limit of XRD. TEM was used to identify the
crystallographic structure of the secondary phase, which was
shown to be cobalt ferrite, CoFe2O4. It is inferred from the data
that the resultant ferromagnetic response identified using VSM
measurements was due to the presence of the minor secondary
phase. The Remanent magnetization at room temperature was
Mr ≈ 76 memu/g which dropped down to almost zero (Mr ≈ 0.8
memu/g) at 460 oC, far lower than the anticipated for CoFe2O4.

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