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|Title: ||Synthesis, structural and property studies of bismuth containing perovskites|
|Authors: ||Chen, Wei-tin|
|Supervisor(s): ||Attfield, J. Paul|
|Issue Date: ||2009|
|Publisher: ||The University of Edinburgh|
|Abstract: ||Several bismuth-containing transition metal perovskites that are of interest as
potential multiferroic materials have been synthesised and studied. These materials
have been structurally characterised and their physical properties have been
examined at varying temperatures and pressures.
The new series of substituted bismuth ferrite perovskites BixCa1-xFeO3, where
x = 0.4 - 1.0, has been prepared. A disordered cubic phase (x = 0.4 - 0.67) and the
coexistence of rhombohedral and cubic phases (x = 0.8 and 0.9) have been observed.
The x = 0.8 sample is located at the phase boundary and shows a transformation from
cubic to rhombohedral symmetry at 473 - 573 K. All samples are antiferromagnets at
room temperature and have Néel temperature of 623 - 643 K. Ferroelectric order is
suppressed in the disordered cubic phase.
BixLa1-xMnO3 materials with x = 0.8, 0.9 and 1.0 were synthesised at 3 - 6 GPa.
For x = 1.0 and 0.9 samples a highly distorted perovskite structure with monoclinic
space group C2/c was adopted and ferromagnetic behaviour was observed with Curie
temperatures of 101 and 94 K, respectively. Bi0.8La0.2MnO3 shows an O'-type
orthorhombic Pnma structure and canted A-type antiferromagnetic ordering below 80 K.
A new phase of BiNiO3 has been discovered at 4 - 5 GPa below 200 K, in which
a Pb11 symmetry has been revealed with a = 5.2515(2) Å, b = 5.6012(3) Å,
c = 7.6202(4) Å and β = 90.20(1) º at 4.3 GPa and 100 K. This new Phase Id is
derived from the ambient Phase I Bi3+
0.5Ni2+O3, where the charge
disproportionated Bi3+/Bi5+ cations become disordered. The updated P-T phase
diagram of BiNiO3 is presented.
BiCu3Mn4O12 has been studied by neutron diffraction from 5 to 400 K. The
incorporation of Mn3+ into the Cu site has been observed, showing that the true
composition is BiCu2.5Mn4.5O12. The ordering of Mn and Cu moments below
transition temperature 320 K is found to be ferromagnetic rather than ferrimagnetic
as proposed previously.|
|Sponsor(s): ||Engineering and Physical Sciences Research Council (EPSRC)|
|Keywords: ||transition metal perovskites|
|Appears in Collections:||Chemistry thesis and dissertation collection|
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