Crystal Chemistry and Dielectric Properties of <TEX>$Bi_4Ti_3O_{12}$</TEX> by the Substitution of Rare Earth Elements (Y, Nd, Sm, Gd)

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J. Korean Ceram. Soc. > Volume 32(10); 1995 > Article

Journal of the Korean Ceramic Society 1995;32(10): 1178.

희토류원소(Y, Nd, Sm, Gd)의 치환에 의한 $Bi_4Ti_3O_{12}$의 결정화학 및 유전물성

고태경, 방규석

인하대학교 무기재료공학과

Crystal Chemistry and Dielectric Properties of $Bi_4Ti_3O_{12}$ by the Substitution of Rare Earth Elements (Y, Nd, Sm, Gd)

ABSTRACT

Bi4Ti3O12 (BIT) and its rare earth (Y, Nd, Sm, Gd)-substituted derivatives were synthesized using a sol-gel method to investigate their microstructures, cystal structures and electrical properties depending on the subsituted elemetns. Nd- or Sm-substitution into BIT appeared to be favorable, while Y- or Gd-substitution occurred with a pyrochlore phase. This suggests that a smaller trivalent rare earth ion may not be favorable in the structure of BIT. The rare earth derivatives showed that their particle sizes and shapes were considerably different depending on the kinds of substituted elements. Y-substitution resulted in developing a relatively even particle size and a dense microstructure. In structure, they may be similar to the pseudo-orthorhombic BIT but close to a paraelectric tetragonal phase. Their a (or b) axes were shortened, compared to the one of BIT. Such a distortion may result a decrease in the tilting of TiO6. BIT and the derivatives showed that their dielectric constants and losses were 40~120 and less than 0.03, respectively in the frequency range of 1~10 MHz. The dielectric loss of Y-substituted derivative was the lowest one and changed a little to frequency. Curie points were observed in all the derivatives like BIT to suggest that they would be ferroelectric. The temperature stability of the delectric properties of the derivatives below the Curie points were relatively better than the one of BIT.

Key words: Bismuth titanate, Rare earth elements, Substitution, Crystal chemistry, Ferroelectric