Study of Barium Titanate Powder Doped of Niobium and Yttrium
Study of barium titanate powder doped of Niobium and Yttrium
Hasegawa H. L., Paulin Filho, P. I., Morelli M. R. Federal University of São Carlos – Departament of Materials Engineering PPG-CEM P.O. Box 676 – 13560-905 – São Carlos – SP – Brazil E-mail: [email protected]
Keywords: ceramic powder, barium titanate, combustion reaction
Abstract From a technological point of view, piezoceramics based in barium titanate (BaTiO3) is one of the most promising candidates to substitute PZT and their variants (Prohibition of heavy metals, like a Pb, Hg and Cr, by worldwide community after 2008). However, the production on a commercial scale is strongly affected by the difficulties in obtaining BaTiO3 units with the desired properties like a curie temperature (Tc) above of 300ºC, electro mechanical coupling factor (K) above of 0.6 and Quality Factor (Qm) above of 300. The solid state formation of barium titanate powder with both Nb and Y doped to promote the abnormal grain growth have been studied with respect to the physical and chemical characteristics of the raw material (approximately single crystal properties). Special attention has been paid to the particle size distribution, particle morphology and dopant levels. Experimental procedures for characterization and discussion were based in micrographs obtaining by scanning electron microscopy, X-ray and specific surface area.
Introduction
Piezoceramics based in barium titanate (BaTiO3) is one of the most promising candidates to substitute piezoelectric ceramics, like a PZT, dielectric ceramics and their variants (PMN-PT, PZN- PT and others), due to the prohibition of heavy metals, like a Pb, Hg and Cr, by worldwide community after 2008. BaTiO3 bulk material is an alternative and environment friendly way to substitute piezoelectric and dielectric ceramics that contain harmful compounds in the composition. However, the production on a commercial scale is strongly affected by the difficulties in obtaining BaTiO3 units with the desired properties [1]. The recent development of preparation of fine ceramics powders has become an important part of modern ceramic research. There is a strongly trend toward the application of different methods for powder synthesis, especially in, electronic ceramics. In spite of a cost with is initially higher than powders prepared from conventional solid-state reaction of mechanically mixed and calcined materials, there are various methods of fine powder preparation like a chemical precipitation route, hydrothermal process, sol-gel process and combustion reaction. Special attention has been paid by scientific community to combustion reaction method due to quickly and easily produces of fine, high purity and high crystalline oxides can be obtained. This type of processing it is considerate a very promising alternative method to produce ceramic powders [1-4]. Some studies show that is possible to increase some electrical properties (like a piezoelectric, dielectric and PTCR effects) of barium titanate ceramics using a fine and homogeneous powders with both Nb and Y doped to promote the abnormal grain growth and have been studied with respect to the physical and chemical characteristics of the raw material (approximately single crystal properties). Special attention has been paid to the particle size distribution, particle morphology and dopant levels. Experimental procedures for characterization and discussion were based on scanning electron microscopy (SEM), X-ray diffraction and measurement of specific surface area and measurement of density [1-4].
Experimental procedure
The powder was obtained starting to the stoichiometric composition of the combustion powder mixture of Ba(Na3)O2, TiO2, NH2CONH2, NH2CONH2, Y2O3 and Nb2O5 calculated by 1:1.0105:0.025:0.23:0.01 molar ratio for yttrium doped powder and 1.0095:1:0.025:0.23:0.01 molar ratio for niobium doped powder. The reactants were mixed in 5 wt% distilled water and the resulting solution was heated on hot plate equipment. Hence, mixture to form foam, which ruptured with emission of a flame, smoke and it, grew to incandescence. The reaction took place approximately 20 seconds and the temperature reached 1100±100°C. The self-propagating flame temperature was directly measured using an optical pyrometer. Barium titanate powder with niobium and yttrium doped obtained by combustion reaction was characterized by X-Ray diffraction pattern (Fig.1), particle size distribution obtained by Sedigraph (Fig. 2 and Table 1), specific surface area were determinate by BET method and the density of both powder were determinate by helium picnometry technique (Table 1) and the flocks morphology was analyzed by scanning electron microcopy (SEM) and their micrographs were show at Fig. 3 to Fig.6.
+ + BaTiO 3
)
.
.u (a) Nb doped (a + + ity + + s
n + te +
In +
(b) Y doped + + + + + + +
15 20 25 30 35 40 45 50 55 60 65 70 75 80 2θ (degrees)
Fig. 1 X-Ray diffraction pattern of bariun titanate powder obtained by combustion reaction (a) doped with niobium and (b) doped with yttrium.
100
90 Combustion BT-Y Combustion BT-Nb 80 70
ss (%)
a 60
M
e 50 v ti a l 40
mu u 30 C 20 10
0 100 10 1 0,1 Equivalent Spherical Diameter (µm)
Fig 2. Particle size distribution (equivalent spherical diameter) obtained by sedigraph of powders obtained by combustion reaction.
Table 1. Equivalent spherical diameter on 50% cumulative mass and specific surface area (obtained by BET technique) and density (obtained by helium picnometry technique) of powders doped by yttrium and niobium.
BaTiO3–Y powder BaTiO3–Nb powder Equivalent diameter (µm) 2.850 3.250 Surface Area (m 2/g ) 3.7538 2.3808 Density (g/cm 3 ) 5.9540 5.8590
10 µm
Fig.3: SEM micrograph of detail of BaTiO3 with yttrium doped flock (5,000X).
500 nm
Fig. 4: SEM micrograph of detail of BaTiO3 with yttrium doped flock (40,000X).
10 µm
Fig. 5: SEM micrograph of detail of BaTiO3 with niobium doped flock (5,000X).
500 nm
Fig. 6: SEM micrograph of detail of BaTiO3 with niobium doped flock (40,000X).
Results and Discussion
The combustion reaction produced fine and high crystalline barium titanate powders and the X-ray diffraction reveals a simple cubic peroviskite structure. This kind of powder preparation is interesting due to high crystalline powder can be obtained and Ba(Na3)O2 does not contain BaCO3, because certain amount of this material can be deteriorate the microstructure of BaTiO3 during the sintering. These results support the conclusion that the combustion reaction is an appropriated and efficient technique for the production of high purity, fine grain and high crystalline BaTiO3 powders.
References [1] T. Yamamoto, Y. Ikuhara, T. Sakuma Materia Japan, 38 (1999), p. 126 [2] S. Young, K. Myung, H., Journal of European Ceramic Society, 17, (1997), p.1725 [3] D.F.K. Henning, R. Jansen, Jour. Am. Ceram. Society, 70, (1987), p. 23 [4] Y. Ohara, K. Koumoto, H. Yanagida, Jour. Am. Ceram. Socciety, 77, (1994), p. 2327
Acknowledgement
The authors wish to thank the CNPq - National Council for Scientific and Technological Development (Brazilian Agency) for financial support in the form of Master Science Scholarship.