Effects of sintering temperature on the dielectric and piezoelectric properties of Sr additive Sm-modified PbTiO3 ceramics
Introduction
In recent years, lead titanate (PbTiO3) ceramics have attracted attentions due to its high Curie temperature of 490 °C and low dielectric constant of about 200, which make them attractive for high-temperature and high-frequency transducer applications than that of PZT ceramic system [1], [2]. However, pure lead titanate ceramics are very difficult to be sintered because of its large lattice anisotropy (c/a=1.064). On cooling through Curie temperature, the large anisotropy of ceramic material becomes fragile. In addition, it is difficult to pole the ceramics with low resistivity (107–108 Ω cm).
By substitution of isovalent (Ca2+, Ba2+, Cd2+, …, etc.) or off-valent (Sm3+, Gd3+, Y3+, …, etc.) ions into the Pb2+ sites, the lattice anisotropy is reduced [3], [4], [5], [6], [7], and the samples become more dense. These modified PbTiO3 ceramics will result in a relatively large thickness electromechanical coupling coefficient, kt, and a small planar electromechanical coefficient, kp (kt⪢kp). In other words, the addition of Ca or Sm into PbTiO3 results in a higher kt/kp ratio compared with PZT ceramics. This property makes it possible that PbTiO3 based ceramics can be used for high-frequency applications such as surface acoustic wave (SAW) devices and piezoelectric transducer [8].
Many researchers reported that (Pb0.85Sm0.1)(Ti0.98Mn0.02)O3 ceramics shows exceptionally large electromechanical anisotropy [9], [10], [11], [12], [13]. The Sm-modified PbTiO3 ceramic with Ca doped was showed to increase the thickness coupling factor, kt [4]. Since Sr and Ca belong to the alkaline-earth metal in the periodic table, and according to author’s knowledge, no one has investigated the Sm-modified PbTiO3 with Sr dopants. In this paper, we prepare (Pb0.88−xSrxSm0.08)(Ti0.98Mn0.02)O3 (x=0.05–0.25) system with additional dopants of Sr to investigate the piezoelectric and dielectric properties by using different sintering temperature from 1125 to 1250 °C.
Section snippets
Experimental procedure
A conventional ceramics preparation procedure was used to prepare the sample. Raw materials were mixed by pure reagent PbO, TiO2, Sm2O3, SrCO3 and MnO2 powders (>99.0% purity). The materials (Pb0.88−xSrxSm0.08)(Ti0.98Mn0.02)O3, x=0.05–0.25, were calcined at 900 °C for 2 h, and excess PbO was added to counteract the volatilization of PbO during firing, then followed by pulverization. After that, the powders were dried and milled with 8 wt.% of a 5 wt.% PVA solution. Then, the samples were pressed
Results and discussion
Fig. 2 shows the bulk density of all samples as a function of the sintering temperature. As the sintering temperature increases, the density of all Sr additive samples increase at first and reaches maximum value as sintering temperature is 1200 °C, then dropped. The SEM patterns of the Sm-modified PbTiO3 ceramics doped and undoped with Sr that sintered at 1200 °C were shown in Fig. 3, and both of them are very dense. Fig. 4 shows the grain size of all samples as a function of the sintering
Conclusions
The additives of Sr and Sm simultaneous cannot only reduce the lattice anisotropy (c/a), but also keep good dielectric and piezoelectric anisotropy properties of the Sm-modified PbTiO3 ceramics. As the samples are sintered at 1200 °C, the density and thickness electromechanical coupling coefficient of the studied samples reach the maximum value, and loss factor keeps smaller than 9.5×10−3. On the other hand, the kt value of the Sr dopants samples that sintered at 1200 °C is about 0.54 for x
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Present address: Tainan Teachers College, Tainan, Taiwan.