Korean Journal of Crystallography (한국결정학회지)

Korean Crystallographic Association (한국결정학회)
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Syntheses, Dielectric Properties and Ordering Structures of $Pb(Fe _{1/2}Ta_{1/2})O_3$

$Pb(Fe _{1/2}Ta_{1/2})O_3$의 합성, 유전특성 및 질서배열구조

  • 우병철 (고려대학교 재료공학부, 한국과학기술연구원 재료연구부) ;
  • 김병국 (한국과학기술연구원 재료연구부) ;
  • 김병호 (고려대학교 재료공학부)
  • Published : 2002.12.01
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Abstract

Single phase $Pb(Fe_{1/2}Ta_{1/2})O_3$, ceramics were successfully synthesized from the powders prepared by solid state reaction (sintering temperature: $1100^{\circ}C$, density: $9.3g/cm^3$, average grain size: $5.1{\pm}1.2mm$, space group: Pm3m). Their dielectric properties measured at $-150{\sim}50^{\circ}C$ showed the maximum relative dielectric constant of 31000 at $-41^{\circ}C$. 1 kHz, and typical relaxor ferroelectrics characteristics such as diffuse phase transition and dielectric relaxation phenomena. However, the diffuseness of phase transition decreased and the dielectric properties became more normal ferroelectrics as the time of annealing at $1000^{\circ}C$ increased. By using Raman spectroscopy, it was revealed that the $Fe^{3+}$ and $Ta^{5+}$ ions in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, are stoichiometrically 1 : 1 ordered within the short-range that can not be probed even by transmission electron microscopy, and this stoichiometric 1 : 1 ordering is enhanced by the annealing. The relaxor ferroelectric characteristics in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, could be correlated with the stoichiometric 1 : 1 short-range ordering of B-site cations, and the decrease of relaxor ferroelectric characteristics in the annealed $Pb(Fe_{1/2}Ta_{1/2})O_3$ could be correlated with the enhanced stoichiometric 1 : 1 short-range ordering of B-site cations.

고상반응법에 의해 합성된 분말을 $1100^{\circ}C$에서 소결함으로써 밀도가 $9.3g/cm^3$이고 평균입경이 $5.1{\pm}1.2{\mu}$인 $Pb(Fe_{1/2}Ta_{1/2})O_3$를 단일상으로 합성하였다. (공간군: Pm3m) $-150{\sim}50^{\circ}C$에서 측정된 비유전율은 인가전압의 주파수가 1kHz일 때 $-41^{\circ}C$에서 비유전율이 3100으로 최대값을 가지고 유전완화(dielectric relaxation)현상 및 완만한 상전이(diffuse phase transition, DPT)가 뚜렷하게 관찰되는 전형적인 완화형 강유전특성을 보였으며 소결후 $1000^{\circ}C$에서의 열처리 시간이 증가함 에 따라 상전이의 완만화도는 감소하여 정상 강유전체화 하였다. 한편, 소결직후 $Fe^{3+}$와 $Ta^{5+}$ 이온은 투과전자현미경으로도 검출할 수 없는 정도의 단거리 영역에서 화학양론적으로 1 : 1 질서 배열하고 있으며 이러한 B자리 양이온의 질서배열은 열처리 시간이 증가함에 따라 강화됨을 라만분광법으로 확인하였다. 소결직후 $Pb(Fe^{12}Ta_{1/2})O_3$센서의 완화형 강유전특성은 B자리 양이온의 화학양론적 1:1 단거리 질서배열구조와, 열처리한 $Pb(Fe_{1/2}TA_{1/2})O_3$에서의 완화형 강유전특성 감소는 열처리에 따라 강화된 화학양론적 1:1 단거리 질서배열구조와 연관지을 수 있었다.

Keywords

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