Dielectric, piezoelectric, and pyroelectric anisotropy in KCl-modified grain-oriented bismuth vanadate ceramics
- PDF / 566,642 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 96 Downloads / 196 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Dielectric, piezoelectric, and pyroelectric anisotropy in KCl-modified grain-oriented bismuth vanadate ceramics K. Shantha and K. B. R. Varmaa) Materials Research Centre, Indian Institute of Science, Bangalore-560 012, India (Received 20 October 1997; accepted 8 June 1998)
The effect of the additive KCl, on the structural, microstructural, and polar properties of bismuth vanadate (BiV) ceramics is investigated. The scanning electron microscopic (SEM) studies reveal a remarkable modification in the microstructure and the occurrence of high grain-orientation (75%) on KCl addition. The energy dispersive x-ray (EDX) analyses indicate the presence of chemically inhomogeneous distribution of KCl, with core-shell-like grain structure. The KCl-modified BiV samples exhibit a broad and depressed phase transition, with no frequency dispersion, as a result of the increased internal stress and the formation of core-shell-like grain structure. Significant anisotropies are observed in the dielectric, piezoelectric, and pyroelectric responses of these grain-oriented ceramic samples. These samples are characterized by near rectangular ferroelectric hysteresis loops, with a significant anisotropy in the Pr (Pr'yPrk 2.43, at 300 K) and Ec (EckyEc' 2.22, at 300 K) values between the directions parallel and perpendicular to the cold-pressing axis.
I. INTRODUCTION
The formation of bismuth vanadate, Bi2 VO5.5 (BiV), crystalline phase, which is a vanadium analog of an n 1 member of the Aurivillius family of oxides, has been reported in the Bi2 O3 –V2 O5 binary system.1– 4 It crystallizes in a non-centrosymmetric, polar orthorhombic class and is ferroelectric at room temperature. Systematic studies carried out, on both the single and polycrystalline samples, confirm that BiV exhibits two reversible phase transitions at 725 and 835 K.5,6 BiV, by virtue of its high ionic conductivity in the high temperature tetragonal phase, has attracted the attention of many researchers for solid state fuel cell applications.7,8 However, the use of these ceramics for polar device applications is inhibited by its high dielectric loss (0.3 at 300 K and 3.5 at 725 K, measured at 100 kHz), arising from its high ionic conductivity, as it hinders effective electrical poling. Our investigations into the effect of various dopants and additives on the physical properties of BiV ceramics have demonstrated that potassium chloride (KCl) as an additive, is effective in modifying the microstructure as well as reducing the electrical conductivity.9,10 Moreover, the electrical poling of the ceramic samples of the Aurivillius family of oxides is found to be ineffective in enhancing their piezoelectric response, since the rotation of the spontaneous polarization is confined to two dimensions, i.e., to the a-b plane. In such ceramic samples, the piezoelectric properties can effectively be improved by the process of grain orientation, achieved a)
http://journals.cambridge.org
II. EXPERIMENTAL DETAILS A. Sample preparatio
Data Loading...
