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Perovskite PMT-PT계의 강유전 특성 및 확산상전이
김연중,Kim, Y.J. 한국진공학회 2008 Applied Science and Convergence Technology Vol.17 No.2
Perovskite 구조의 PMT-PT계 고용체를 precursor columbite를 이용한 산화물 혼합법으로 제작하여 결정립의 성장과 상전이 현상을 분석하였다. $1250^{\circ}C$에서 4시간 유지하여 제작한 시편의 소결밀도는 이론밀도의 97% 이상이었고, 완전한 perovskite phase를 형성하였다. 치밀하게 소결 처리된 시편의 결정립의 크기는 $6\sim8{\mu}m$로 측정되었다. PMT-PT 고용체계는 복합 강유전 고용체의 전형적인 P-E 이력현상과 강한 진동수 분산특성이 관찰되었다. 특히 PMT가 70% 이하인 조성은 상전이 온도 이상에서도 자발분극이 완전히 소멸하지 않는 relaxor 특성을 보였으며, 유전상수와 유전손실의 큰 진동수 의존성을 보였다. Ferroelectric properties of the PMT-PT were also studied from the temperature dependence of hysteresis loops using a method slightly modified from Sawyer-Tower's. Dielectric, pyroelectric and piezoelectric properties of the ceramics in the system PMT-PT were investigated. The resulted densities of the PMT-PT ceramics system were greater than 97 % of the theoretical value. As observed SEM micrograph of the fracture surfaces of the PMT-PT ceramics system, the average grain sizes were increased about 3-5 ${\mu}m$ to 6-8 ${\mu}m$ with increasing sintering temperature. The specimens with PT<0.30 for PMT-PT solid solution system exhibited the dielectric and pyroelectric properties of a typical relaxor ferroelectrics. The composition with the maximum dielectric constant exhibits relatively superior pyroelectric and piezoelectric properties.
Dielectric Characteristics of PbSc1/2Nb1/2O3 Prepared by Using the One-step Solid State Reaction
김연중 한국진공학회 2016 Applied Science and Convergence Technology Vol.25 No.4
The PbSc1/2Nb1/2O3 ceramics at a relatively low temperature of 1300oC was successful synthesized. Solid state reaction of two-step process is not necessary. The dielectric constant, dielectric loss and admittance of ceramic samples were determined. The pyroelectric characteristics are in good agreement with the dielectric properties. Ferroelectric properties of well-formed the PbSc1/2Nb1/2O3 ceramics are in agreement with broad distribution of relaxation phenomenon. Relatively strong frequency dependent of dielectric constant is observed at about 110oC. The distinct thermal hysteresis was observed in the measurement of the dielectric constant and dielectric loss. The critical exponents of during cooling and heating measurements in the PbSc1/2Nb1/2O3 ceramics were 1.14 and 1.59 at 1 kHz, respectively.