Barium Titanate Ceramic/Ceramic 0-3 Composites for Ultrasonic Transducer Applications
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with thickness up to several microns by the conventional sol-gel method. Recently, a modified sol-gel technique has been developed for preparing PZT films of thickness up to 60itm7 . In this method, nano-sized ceramic particles are dispersed in a sol-gel matrix of the same kind of ceramic. The resulting ceramic/ceramic composite films have a 0-3 structure where "0" indicates that the particles are not inter-connected in any direction and "3" means that the matrix is connected in all directions.
EXPERIMENTS The BaTiO 3 powders and films were prepared by a sol-gel method. The process involved the mixing of Ti-isopropoxide and Ba-acetate in deionized water under a continuous stirring at room temperature. The amount of Ti-isopropoxide and Ba-acetate was in a molar ratio of 1:1. In order to avoid precipitation, a tiny amount of acetic acid, acetylacetone and glycerin were added. The concentration of the final solution was about 0.8M. Fig. I shows the procedure for preparing the BaTiO3 powder and films by the sol-gel process. The BaTiO 3 gel was obtained by drying in an oven at 100°C for 12h and then annealed at different temperatures to obtain the BaTiO 3 powder. The crystallization process of the BaTiO 3 gel was studied by x-ray diffraction (XRD, Philips x'pert XRD system), differential thermal 347 Mat. Res. Soc. Symp. Proc. Vol. 574 ©1999 Materials Research Society
Sstirring Add stoichiometric amount of Titanium (IV) Iso-propoxide • stirring Add glycerin
! Sstirring•/ ,
348
RESULTS AND DISCUSSION The XRD patterns in Fig 2(a) show that the BaTiO 3 powder annealed below 650'C exhibits a typical amorphous structure. When the annealing temperature increases to 700*C, crystalline peaks of BaTiO 3 appear. This agrees with the DTA and TGA results (Fig.3(a)) which show a peak around 700*C in the DTA curve with no corresponding weight loss in the TGA curve. Fig. 2(b) gives the XRD pattern of the BaTiO 3 0-3 composite films annealed at different temperatures. The films start to crystallize at 700*C. The peaks at 20 = 440 and 500 are due to the stainless steel substrate.
(a)
S•
1200 C
850 c
- ..
0750
,
•
,
1000 C
,•,
:,
906,C ., 800 C.
C
,
800 C
650 C
750C C' 700 C 650C 6WC
40
3,0
20
20
60
50
30
40
550 c 60
50
20
20
Fig.2 XRD patterns of (a) BaTiO 3 powder and (b) BaTi433 films annealed at different temperatures. 40
(b)
492 612.4 492.. 713
360.2
(a) (a
VI
I 80-
30
87.5
25
695.3 589.7
40O
20
BaT103 Gel Scanmte: 10deg/min
15 .vIII
45.
60O
,
I
100
•
I
200
i
I
300
I
.BaTiO3 Gel 20 Scan rate: 10.0deg/rnin
wt: 19.53nmg I
400
I
I
I
I
%500 600
Temperatfre ( C
I
I
700
I
100
200
300
400
wt: 6. 521rng 500
TWeprtr (C)
Fig.3 (a) A DTA curve and (b) a TGA curve of BaTiO 3. 349
600
700
Fig. 4 shows the microstructure of the surface of the film in a scanning electron microscope (SEM, Stereoscan 440). In Fig. 4(a), the film was heat-treated at 700°C for 30min and the surface was smooth. For the films heat-treated at 850'C for 30min, granular grains (size 40nm)
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