비화학양론 Sr_(1±x)Bi_(2±y)Ta_(2)O_(9)과 Sr_(1±x)Bi_(2±y)Nb_(2)O_(9) 세라믹의 유전 및 압전 특성
Dielectric and Piezoelectric Properties of Nonstoichiometric Sr_(1±x)Bi_(2±y)Ta_(2)O_(9) and Sr_(1±x)Bi_(2±y)Nb_(2)O_(9) Ceramics
비화학양론 세라믹 유전 압전;
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Many lead-based compounds such as PZT[Pb(Zr,Ti)O_(3)] have been widely used for electronic ceramic parts such as dielectric or piezoelectrics. However, lead(Pb) inflicts a bodily injury and leads to serious environmental pollution. And, in case of PZT, 90 degree domains was generated from paraelectric to ferroelctric phase transition. So that the poling process is required for better piezoelectric and ferroelectric properties. Consequently, development of Pb-free and 90 degree domain-free materials is required. For this reason, bismuth layer ferroelctrics which have been studied for ferroelectric random access memories applications were considered to be candidate materials. Bismuth layered ferroelctric materials such as SBT or SBN ceramics are represented by (Bi_(2)O_(2))^(2+)(A_(m-1)B_(m)O_(3m+1))^(2-), m=2. And these materials generally have higher Curie temperature (T_(c)) than PZT. Ferroelectric properties such as the remanent polarization(P_(r)) and T_(c) have been found to depend on the Sr/Bi content ratio. It was reported that the nonstoichiometric compositions with Sr-deficient/Bi-excess have better ferroelctric properties than the stoichiometric compound. Bismuth layer structured ferroelectrics (BLSFs) such as SBN or SBT ceramics are adequate for the fine tolerance oscillator applications since piezoelectric properties of these materials have a low electromechanical factor and a high mechanical quality factor than PZT. In this work, Sr_(0.55)Bi_(2.3)Ta_(2)O_(9), Sr_(0.7)Bi_(2.2)Ta_(2)O_(9), SrBi_(2)Ta_(2)O_(9), Sr_(1.2)Bi_(1.8)Ta_(2)O_(9), Sr_(0.55)Bi_(2.3)Nb_(2)O_(9), Sr_(0.7)Bi_(2.2)Nb_(2)O_(9), SrBi_(2)Nb_(2)O_(9), and Sr_(1.2)Bi_(1.8)Nb_(2)O_(9) ceramics were prepared by solid state reactions. The effects of nonstoichimetry on the crystal structure, Curie temperature, dielectric and piezoelectric properties were investigated. X-ray diffraction analysis indicated that single-phase of Bi-layered perovskite was obtained. The Curie temperarue of SBN(SBT) rose from 414℃(314℃) to 494℃(426℃) when Sr/Bi content ratio was increased. in the case of Sr/Bi content ratio = 0.55/2.3, the maximum value of the mechanical quality factor Qm of SBT and SBN wre obtained 3320 and 1010, respectively.
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