Synthesis of ferroelectric nanocrystalline SrBi
2
Ta
2
O
9
powder by the colloid-gel process
Chung-Hsin Lu*, Susanta Kumar Saha
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.
(Refereed)
Received 25 October 1999; accepted 23 March 2000
Abstract
An innovative colloid-gel process using inorganic salts as starting materials has been successfully
developed for preparing ferroelectric strontium bismuth tantalate (SrBi
2
Ta
2
O
9
) powder. This new tech-
nique began with the preparation of a mixture of Ta(OH)
5
colloid with the aqueous solutions of strontium
and bismuth cations, followed by the addition of ethylene glycol and citric acid as gel-forming reagents.
During the calcination process the fluorite phase was formed as an intermediate that was subsequently
converted into the SrBi
2
Ta
2
O
9
phase. After calcination at 750°C, pure ultrafine SrBi
2
Ta
2
O
9
polycrystalline
powder with a narrow particle size distribution was obtained. The primary particle size of the obtained
SrBi
2
Ta
2
O
9
powder was around 40 nm. In comparison with the solid-state reaction, the newly developed
colloid-gel process significantly reduces the heating temperature for synthesizing SrBi
2
Ta
2
O
9
, as well as
the particle size of the obtained powder. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: A. Ceramics; A. Electronic materials; B. Sol-gel chemistry; C. Electron microscopy; C. X-ray diffraction
1. Introduction
In recent years, bismuth layered-structured ferroelectric materials such as SrBi
2
Ta
2
O
9
and
Bi
4
Ti
3
O
12
have become important candidates for application in nonvolatile ferroelectric
random access memories (FeRAM) due to their low coercive field and low leakage current
density. SrBi
2
Ta
2
O
9
has great potential for use in FeRAM devices because it exhibits
fatigue-free characteristics up to about 10
12
switching cycles [1–3]. SrBi
2
Ta
2
O
9
belongs to
the family of so-called multilayered interstitial compounds having the general formula
* Corresponding author. Fax: +886-2-2362-3040.
Pergamon Materials Research Bulletin 35 (2000) 2135–2143
0025-5408/00/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0025-5408(00)00422-0