Effects of sintering temperature on the dielectric and piezoelectric properties of Sr additive Sm-modified PbTiO3 ceramics

https://doi.org/10.1016/S0924-4247(02)00382-5Get rights and content

Abstract

(Pb0.88−xSrxSm0.08)(Ti0.98Mn0.02)O3 ceramics; x=0.05–0.25 were prepared by conventional mixed-oxide technique, with sintering temperature at 1125–1250 °C. Microstructural and compositional analyses of these doped ceramics have been carried out using X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects of dopants and the sintering temperature on the piezoelectric and dielectric properties of Sm-modified PbTiO3 ceramics have been investigated. We successfully showed that all Sr additive samples have maximum density and thickness electromechanical coupling coefficient, kt (>0.55) at 1200 °C sintering temperature, and still keep small planar electromechanical coupling coefficient, kp. In other words, the optimum sintering condition was found.

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 (ktkp). 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

References (16)

  • S Ikegami et al.

    Electromechanical properties of PbTiO3 ceramics containing La and Mn

    J. Acoust. Soc. Am.

    (1971)
  • T Takahashi

    Lead titanate ceramics with large piezoelectric anisotropy and their application

    Ceram. Bull.

    (1990)
  • H Takeuchi et al.

    Electromechanical properties of (Pb,Ln)(Ti,Mn)O3 ceramics

    J. Acoust. Soc. Am.

    (1982)
  • K. Takeuchi, D. Damjanovic, T.R. Gururaja, S.J. Jang, L.E. Cross, Electromechanical properties of calcium-modified lead...
  • J Shenglin et al.

    Investigation on anisotropy in piezoelectric properties of modified PbTiO3 ceramics

    Piezoelectr. Acoust.

    (1995)
  • I Ueda et al.

    Piezoelectric properties of modified PbTiO3 ceramics

    Jpn. J. Appl. Phys.

    (1968)
  • Y Yamashita et al.

    (Pb,Ca)[(Co1/2W1/2),Ti]O3 piezoelectric ceramics and their applications

    Jpn. J. Appl. Phys.

    (1981)
  • O Ohnishi et al.

    Piezoelectric ceramic transformer operating in thickness extensional vibration mode for power supply

    IEEE Ultrason. Symp.

    (1992)
There are more references available in the full text version of this article.

Cited by (41)

  • The influence of sintering temperature on the microstructures and electrical performances of BCZT ceramics

    2020, Materials Letters
    Citation Excerpt :

    With the increase of sintering temperature and driven by grain boundary migration, the number of pores will be eliminated to a certain extent to achieve the densification of samples. In addition, the energy of defect formation decreases, which is conducive to the formation of point defects (oxygen vacancy) [13,14]. The movement of oxygen vacancies along grain boundary directly results in the diffusion and fusion of multiple small pores at grain boundaries, which reduces the density and grain size of samples sintered at 1330 °C [15].

  • Large pyroelectric figure of merits for Sr-modified Ba<inf>0.85</inf>Ca<inf>0.15</inf>Zr<inf>0.1</inf>Ti<inf>0.9</inf>O<inf>3</inf> ceramics

    2016, Solid State Sciences
    Citation Excerpt :

    Moreover, the higher values of dielectric constant for BCZT-Sr(15%) can be associated with a competing effect among internal stress, porosity and grain size. It is established in literature that the substitution of isovalent (Ca2+, Sr2+, Cd2+, etc.) into Ba2+ can lead to reduced lattice anisotropy and ceramics become more dense which increases dielectric constant [37,40]. The systematic investigation of dielectric behavior and phase transition are discussed as follows.

  • Enhanced dielectric and piezoelectric properties of BZT-BCT system near MPB

    2014, Ceramics International
    Citation Excerpt :

    Less porosity is observed at 1400 °C sintering temperature. It can be explained according to the phenomenological kinetic grain growth equation that with the increase in sintering temperature the grain size increases [32]. Fig. 5.1 shows the frequency dependence of dielectric constant (εr) of the MPB composition of (BZT–BCT) system, sintered at 1400 °C.

View all citing articles on Scopus
1

Present address: Tainan Teachers College, Tainan, Taiwan.

View full text