Multiferroics

m46.o03 m46.o04
Relaxor behaviour in the system (1-x) Proper ferroelectric transition in the
Ba1-xBi2x/3TiO3 + x Ba1-y Y2y/3TiO3 multiferroic YMnO3
K. Taïbi*, C. Abdellaoui*, A. Guehria-Laidoudi*, Gwilherm Nénert1, Yang Ren2, Michael Pollet3,
A. Simon** and J. Ravez** Björn Hauback4, Ibério P.R. de Moreira5, Sylvain Marinel6,
Harold T. Stokes7, Thomas T.M. Palstra1
* Faculté de Chimie, U.S.T.H.B., BP 32 El-Alia, Bab-Ezzouar, Alger,
Algerie. ** I.C.M.C.B.-C.N.R.S., 87 avenue du D’ A. Schweitzer, 33608 1
Solid State Chemistry Laboratory, Materials Science Centre, University
Pessac, France. E-mail: taibikameldz@yahoo.fr of Groningen, Nijenborg 4, 9747 AG Groningen, The Netherlands,
2
X-ray Science Division, Advanced Photon Source, Argonne National
Keywords: lead-free, ferroelectric relaxor, perovskites Laboratory, Argonne, Illinois 60439, USA, 3ICMCB - CNRS Physico-
Chime des Oxides Conducteurs, 87 Avenue du Doctor Schweitzer 33608
Pessac Cedex France, 4Physics Department, Institute for Energy Technology,
Relaxor ferroelectrics are used for applications in a wide variety P. O. Box 40 2027 Kjeller, Norway 5Departament de Química Física and
of devices [1]. The great interest of these materials is related CeRQT, Universitat de Barcelona, Martí Franquès 1, 08028 Barcelona,
to their very high dielectric permittivity observed in the large Spain, 6CRISMAT - ENSI Bd Maréechal Juin - 14050 Caen Cedex; France,
7
range of temperature and the strong frequency dispersion at Department of Physics and Astronomy, Brigham Young University, Provo,
low temperature [2]. To understand the origin of this behaviour Utah 84602-4650, USA
many works based on structural and physical models are
performed. The relaxor behaviour occurs generally in complex Keywords: multiferroic, ferroelectrics, phase
perovskite of formula (A’A’)’(B’B’’)O3 where two (or more) transitions
cations of different valences are located in the equivalent crystal-
lographic positions. Relaxor materials actually used are lead- Compounds presenting coexistence of ferroelectricity and
based ceramics which present a disadvantage due to the toxicity magnetism have interesting properties allowing the manipu-
of PbO. The actual evolution of research is oriented to environ- lation of electric and magnetic moments by magnetic and electric
ment-friendly application. In this way, the present work concerns fields, respectively. These compounds are called multiferroics.
new lead-free compositions of non-stoichiometric perovskite While a lot of effort has been put into the search and design of
derived from the well known BaTiO3. new multiferroics, the nature of the mechanism of ferroelec-
Dense ceramics were obtained by conventional mixed oxide tricity and thus the nature of the coupling between the different
method. Room temperature X-ray diffraction analysis allowed degrees of freedom is still not well understood [1]. Among the
us to determine the limits of solid solution. Dielectric measure- multiferroics, the hexagonal (h-) RMnO3 are particularly inter-
ments were performed on ceramic disks. For all samples, the esting due the high polarization at room temperature (PS∼5.5
temperature and frequency variations of the real and imaginary C/cm2). The h-RMnO3 exhibit TFE∼1000 K and TN∼100 K. We
part of permittivity are investigated. The results are discussed have studied above room temperature the parent compound
and compared to previous works concerning the Ba1-xA2x/ YMnO3 of h-RMnO3 family. We observed for the first time
3TiO3 compositions where La and Bi are in the dodecahedral
using single-crystal high resolution synchrotron data, powder
sites (A) [3,4]. The performed study has shown that the relaxor neutron diffraction, and dilatometry two phase transitions in
behaviour is not due only to the B-site order/disorder. The role YMnO3 associated with the ferroelectric transition and a tripling
of the cation in the A-site seems to be also important [5]. of the unit cell [2,3]. Using a complete group theoretical analysis
and structure calculations, we identify the transition from a
[1] K. Uchino, Ferroelectrics, 151(1994) 321. centrosymmetric to a ferroelectric state for the hexagonal
[2] L.E Cross, Ferroelectrics, 151, (1994) 305. RMnO3 as the succession of two paraelectric phases namely
[3] J. Ravez and A. Simon, Solid State Science, 2 (2000) 525. P6 3 /mmc (high temperature) and P6 3 /mcm (intermediate
[4] F. Bahri, A. Simon, H. Khemakhem and J. Ravez, Phys.Stat.Sol., temperature) and one ferroelectric phase with P63cm symmetry
184,2 (2001) 459. (room temperature) [2,4]. We prove that this family of
[5] A. Kerfah, K. Taïbi, A. Guehria-Laïdoudi, A. Simon and J. ravez, compounds is not improper ferroelectrics but proper ferro-
Solid State Sciences, accepted, September, (2005).
electrics in agreement with the magnitude of the polarization.
The polarization can be described by a correlated zigzag tilting
of the MnO5 polyhedra due to the displacements of the apical
oxygens instead of the basal plane oxygens.

[1] J.Wang, et al., Science 299, 1719 (2003); T. Kimura et al., Nature
426, 55 (2003) and N. Hur et al., Nature 429, 392 (2004).
[2] G. Nénert, Y. Ren, B. Hauback, H. T. Stokes, I. de P. R. Moreira,
S. Siefert and T. T. Palstra, submitted to Phys. Rev. B., cond-mat/
0504546.
[3] G. Nénert, M. Pollet, S. Marinel, Y. Ren, A. Meetsma and Thomas
T. M. Palstra, submitted to Phys. Rev. B, cond-mat/0601547.
[4] G. Nénert, H. T. Stokes, J. Pérez-Mato and T. T. M. Palstra, in
preparation.

23rd European Crystallographic Meeting, ECM23, Leuven, 2006 Page s121