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Dielectric and morphological studies of BST ferroelectric ceramics

A. IOACHIM1,* , F. VASILIU1, M. I. TOACSĂN1, L. NEDELCU1, M. G. BANCIU1, H. V. ALEXANDRU2, G. STOICA3

Affiliation

  1. National Institute of Materials Physics, P.O. Box MG-7, RO 077125, Bucharest-Magurele, Romania
  2. University of Bucharest, Faculty of Physics, Romania
  3. S.C. Armtech S.A., Curtea de Argeş, Romania

Abstract

Barium strontium titanate with molar formula Ba0.75Sr0.25 TiO3 (BST) was prepared from raw materials by solid-state reaction. Samples were sintered at 1230 oC and 1260 oC for 2 h. In order to improve the sintering process, 1 wt. % MgO and 1 wt. % MnO2 were used as sintering additives. The sinterability, structural, morphological and dielectric properties of pure and doped BST samples were investigated. Perovskite structure of polycrystalline BST ceramics was determined by Xray diffraction. SEM investigations revealed a grain and pore size distribution, which is shifted to higher values by a slight increase of the sintering temperature from 1230 oC to 1260 oC. In the presence of additives, a better sintering and grain refining could be observed, whereas their lack induce a strong effect of exaggerated grain growth, by forming of large faceted grains. The presence of Mn ions in the doped BST ceramics was revealed by the EDX analysis. On the other hand, Mg ions are not evidenced. Temperature dependence of dielectric constant measured at 1 kHz shows a diffuse ferroelectric-paraelectric transition, which can be attributed to the large size dispersion of grains. The increase of sintering temperature leads to a shift of the Curie temperature to higher values..

Keywords

Barium strontium titanate, Ceramics, Ferroelectric-paraelectric transition.

Submitted at: Nov. 14, 2006
Accepted at: May 15, 2007

Citation

A. IOACHIM, F. VASILIU, M. I. TOACSĂN, L. NEDELCU, M. G. BANCIU, H. V. ALEXANDRU, G. STOICA, Dielectric and morphological studies of BST ferroelectric ceramics, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 5, pp. 1576-1581 (2007)