INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER
J. Phys.: Condens. Matter 14 (2002) 11849–11857 PII: S0953-8984(02)39832-1
Magnetic-field-induced orientation in Co-doped
SrBi
2
Ta
2
O
9
ferroelectric oxide
C Bedoya
1
, Ch Muller
1,3
, F Jacob
1
, Y Gagou
1
, M-A Fremy
1
and
E Elkaim
2
1
Laboratoire Mat´ eriaux et Micro´ electronique de Provence (L2MP), UMR CNRS 6137,
Universit´ e de Toulon et du Var, BP 132, F-83957 La Garde Cedex, France
2
Laboratoire pour L’Utilisation du Rayonnement Electromagn´ etique (LURE), Universit´ e de
Paris Sud, Bˆ at. 209D Centre Universitaire, BP 34, F-91898 Orsay Cedex, France
E-mail: muller@univ-tln.fr
Received 22 July 2002, in final form 8 October 2002
Published 1 November 2002
Online at stacks.iop.org/JPhysCM/14/11849
Abstract
Co-doped SrBi
2
Ta
2
O
9
(SBT) compounds have been synthesized using solid-
state reaction between the starting oxides Bi
2
O
3
, Ta
2
O
5
and CoO and the
carbonate SrCO
3
. High-resolution x-ray diffraction data were collected on
a four-circle diffractometer using synchrotron radiation. The structure of the
orthorhombic phase (space group A
1
2am, one formula unit, a = 5.5194
(1)
Å,
b = 5.5191
(1)
Å and c = 25.0309
(2)
Å) has been refined using the Rietveld
method. Chemical occupancies, atomic positions and spontaneous polarization
were deduced from the structural refinement. In order to determine the effects on
ferroelectric properties of the Sr-by-Co substitution, the dielectric response was
measured over the temperature range 450–750 K on heating and cooling and at
several frequencies. Finally, the magnetic field effect on Co-doped SBT powder
was investigated by means of x-ray diffraction. It appears that the magnetic field
induces a strong fibre texture, with the c-axes of grains being aligned with the
direction of the applied field. This original and unusual phenomenon suggests
a new method for the deposition of SBT thin films with enhanced ferroelectric
properties.
1. Introduction
Non-volatile memories using ferroelectric film have attracted a lot of attention in recent years
and are proposed as next-generation memory material [1–3]. Ferroelectric SrBi
2
Ta
2
O
9
(SBT)
thin films are largely studied on account of their fatigue-free properties and low coercive
field [4–6] in comparison to the PbZr
1-x
Ti
x
O
3
(PZT) oxides. To obtain ferroelectric thin films
3
Author to whom any correspondence should be addressed.
0953-8984/02/4511849+09$30.00 © 2002 IOP Publishing Ltd Printed in the UK 11849