Frequency dependence of AC conductivities of KNbVO single crystals

Lee, Sudae,Lee, Chanku,Sul, Chungsik,Bae, Sehwan 東亞大學校附設基礎科學硏究所 1998 基礎科學硏究論文集 Vol.15 No.1

AC conductivity of KNbVO(χ=0, 0.01) was measured at temperatures from 30℃ to 430℃ in the frequency range from 10㎐ to 10㎒. Below 1㎒, the AC conductivity σ(ω) is proportional to ω. The frequency exponent s is a decreasing function of temperature and tends to unity at low temperatures. Frequency dependence of σ and s in both samples is reasonably interpreted by the correlated barrier hopping model. Arrhenius plotting of σ(T) yielded a curved line and from these results the activation energies were estimated to be 1.02eV(for pure KNbO₃), and 0.8 eV (for KNbVO) respectively.

비정질 As₂Se₃ 박막에 첨가된 은이 전기 및 광학적 성질에 미치는 효과

이찬구(Chanku Lee),이수대(Sudae Lee),김덕훈(Douk Hoon Kim),문정학(Jung Hak Mun) 한국안광학회 1996 한국안광학회지 Vol.1 No.2

D.c conductivity and optical transmittance of amorphous (As₂Se₃)Agx (x=0, 2, S, l0mol%) thin films were measured in order to find effects of Ag additives on electrical and optical properties of the films. The d.c. activation energy and the optical gap decreased with increasing Ag contents the Urbach tail was approximately unchangeable for variation of Ag contents. For Ag contents of 5mol% and less, the rate of decrease of the d.c activation energy was more rapidly than that of the optical gap with increasing Ag contents. For Ag contents more than 5mol%, the rate of decrease of the d.c activation energy and the optical gap were nearly the same each other with decreasing Ag contents. So it was appeared that the Fermi level of the films comes close to the mobility edge for Ag contents of 5mol% and less, and the mobility edge comes close the Fermi level for Ag contents more than 5mol%.

Preparation of a carbon membrane with a polymer blend having different thermal stability

Lee, Hong-Joo,Kim, Dong-Pyo,Suda, Hiroyuki,Haraya, Kenji 한국공업화학회 2005 응용화학 Vol.9 No.2

LiNbO₃ 단결정을 이용한 압전진동자 제작의 최적 조건

이수대,설정식,손종윤 慶南大學校 附設 基礎科學硏究所 1996 硏究論文集 Vol.9 No.-

We studied the method to find the optimal manufacturing conditions for the longitudinal and the transversal piezoelectric vibrators with LiNbO₃ single crystal. We calculated the magnitude of strain due to the antipiezoelectric effect at spherical coordinates. And then it is projected to the plane by the stereographic projection method. From these charts, we found the directions with the maximum value of vibrational efficiency and with the minimum value of vibrational noise for the applied electric field. The optimal directions with minimum noise for the longitudinal piezoelectric vibrator are (10.0°, 19.3°), (10.0°, 139.3°), (10.0°, 259.3°). Strain of longitudinal mode of these optimal directions is ??. The ratio of noise to the signal of this vibrator is 0.68%. The optimal directions with minimum noise for the transversal piezoelectric vibrator are (76.2°, 70.1°), (76.2°, 190.1°), (76.2°, 310.1°), and strain of transversal mode is ??. In this case, the ratio of noise to the signal is 0.68%.

LiTaO₃ 단결정의 임피던스 완화현상에 관한 연구

이수대,설정식 慶南大學校 附設 基礎科學硏究所 1996 硏究論文集 Vol.9 No.-

The impedance relaxation of LiTaO₃ single crystals has been studied as a function of frequence range from 10 Hz to 10 MHz at temperatures range from 30 to 1000℃. The complex impedance data were analyzed in Cole-Cole type equivalent circuits by the computer fitting method. It was found that two dispersion processes with non-ideal relaxation had been existing in LiTaO₃ single crystal. one due to the carrier mobility and the other resulting from intrinsic polarization of ferroelectric material. Based on an equivalent circuit the impedance relaxation expression was proposed to describe the impedance behavior of LiTaO₃ single crystals. From this study. activation energy for relaxation process was 1.15eV and relaxation time was about 10-5 sec.

SrTiO₃박막 혼정의 전기적 특성

이찬구,이수대 慶南大學校 附設 基礎科學硏究所 2000 硏究論文集 Vol.14 No.-

SrTiO₃ thin film were deposited on Pt/Ir/SiO₂/Si substrate by RF-magnetron sputtering method. To investigate the effects of annealing temperatures, thin films were annealed in flowing O₂ at temperatures from 550℃ to 650℃ for 30 min. The electrical properties of the annealed samples were strongly dependent on the annealing temperatures. The anomalous behaviour of the conductivities have been observed in the temperature range from 20 to 550℃. It is suggested that the conductivity peaks are related to the movement of oxygen ion or vacancies. The frequency dependent ac conductivity has been explained on the basis of potential barriers formed by the hopping conduction at intercrystalline regions. In the temperature range, a hopping conduction having the activation energy of about 1.72 eV became dominant

Pb Ge Ti O 단결정의 상전이와 유전적 성질

이찬구,이수대,설정식 慶南大學校 附設 工業技術硏究所 1997 硏究論文集 Vol.15 No.1

강유전체 ?? 단결정을 χ=0.015, 0.021, 0.03의 조성에 대하여 Czochralski법으로 성장시켰으며, 성장시킨 단결정의 색상은 맑고 투명한 연한 노란색이었다. ?? 단결정의 유전상수와 자발분극의 온도특성을 조사하기 위하여 온도를 올리면서 실온에서 Curie 온도 위까지 측정하였다. 유전상수의 온도의존성에 대한 조사결과 ?? 단결정의 상전이 온도는 178℃, Curie상수는 c=1.17×10⁴K였다. χ=0.015인 단결정은 ??=152℃, Curie상수는 1.15×10⁴K이며, χ=0.021인 단결정은 ??=137℃, Curie상수는 1.25×10⁴K이고, χ=0.03인 단결정은 ??=142℃, Curie상수는 7.51×10³K이었다. 또한 ?? 단결정의 전기이력곡선 으로부터 얻은 자발분극 ??는 0.047 C/m²이고, 항전기장 ??는1.5×?? V/m이었다. 그리고 ?? 단결정의 자발분국은 ??는 0.025C/m²이고 항전기장은 ??는 1.1×?? V/m이었다. 한편 ?? 단결정의 상유전-강유전 상전이형태는 변위형과 질서-무질서형의 중간적 성질을 가졌다. Ferroelectric ??(χ=0, 0.015, 0.021, 0.03) single crystals were obtained from the melt by the Czochralski method. Grown crystals were pale brownish yellow and fully transparent. The temperature characteristics of dielectric constants, spontaneous polarization of ?? single crystals have been investigated in detail from room temperature up to above the Curie temperature. From the results of the these measurements, the following constants were obtaind : the Curie constant calculated from the slope above ?? are c=1.17×104 K, 1.15×104 K 1.25×104 K and c=7.51×103 K for χ=0, 0.015, 0.021 and χ=0.03 single crystals respectively. The spontaneous polarization ?? and the coercive electric field ?? estimated from the hysteresis loops which are 0.047 C/m², 1.5×?? V/m for ?? single crystal and 0.025 C/m², 1.1×?? V/m for ?? single crystal respectively. From the complex dielectric measurements and pyroelectric measurements. it was confirmed that the paraelectric-ferroelectric phase transition of ?? single crystals undergo a displacive second order phase transition at ??.

강탄성 Switching에 의한 격자점의 변위 특성을 이용한 Pb₃(PO₄)₂ 단결정의 자발변형 측정

이수대,설정식 慶南大學校 附設 基礎科學硏究所 1996 硏究論文集 Vol.9 No.-

In order to measure components of the spontaneous strain tensor by the switching phenomena of Pb₃(PO₄)₂ single crystals, we derived the formulae for translational displacement and rotational displacement of the lattice points by switching between each states in ferroelasticity. By using this formulae, we suggested the method and the process for measurement of components of the spontaneous strain tensor. The value of es11 was measured from the variation of radial component and the variation of azimuthal angle by switching between each states at Pb₃(PO₄)₂ single crystals and it was -0.0217±0.0001. In addition, the value of es13 which was measured from the variation of zenithal angle was 0.0066±0.0001.

(NH₄)₃H(SeO₄)₂ 단결정의 강탄성 스위칭을 일으키는 최적 방향

이수대,손종윤,설정식 경남대학교 신소재연구소 1999 論文集 Vol.11 No.-

mF2/m으로 전이하는 순사한 강탄성체인 (NH4)3H(Se04)2 단결정의 가능한 강탄성 배향상태와 각 배향상태가 갖는 자발변형텐서를 구하였다. 이 자발변형텐서로부터 임의의 정육면체형으로 자른 PG의 시료가 FG에서 갖는 변형을 살펴보았다. 강탄성상에서 스위칭을 일으키는 힘을 가하는 방향에 따른 스위칭력에 대한 크기의 공간분포도를 스테레오 그래픽 프로젝션 기법을 사용한 공간투영도로부터 스위칭을 위한 최적방향을 구하였다. We have calculated the possible ferroelastic orientation states and the spontaneous strain tensor of each orientation state in pure ferroelastics (NH₄)₃H(SeO₄)₂single crystal which belong to 3mF2/m. From this spontaneous strain tensor, we have found the strain which deform from prototypic point group to the ferroelastic point group in cubic PG phase sample. We have sought the optimal direction for ferroelastic switching by the stereographic projection contour to the variation of the free enthalphy per unit volume and per unit pressure as to the direction applied the stress.

Hot Press법으로 제조한 PLZT 세라믹의 유전적 성질

이찬구,안형주,이수대 慶南大學校 附設 基礎科學硏究所 2002 硏究論文集 Vol.16 No.-

Hot press법으로 PLZT(X/65/35) 세라믹을 제조하였으며, La=8 at.%에서 매우 투명한 세라믹을 얻었다. 유전적 성질은 측정온도 216℃∼130℃(x=5∼8)에서 유전율의 최대값의 모양이 퍼짐형을 나타내는 전형적인 완화형 강유전체임을 보였다. P-E 측정에서 잔류분극과 항전기장은 온도가 증가함으로 점진적으로 감소하였다; 즉 두 물리량의 변화는 유전상수의 최대값에 의해 정의된 큐리온도 위의 한계치를 가지는 것을 의미한다 PLZT(X/65/35) ceramics were fabricated by hot press method, and transparent PLZT ceramics were obtained in the composition 8 at.% La. The dielectric properties of PLZT were found to be typical of a ferroelectric relaxor exhibiting a broad maximum of the permittivity at 216℃∼130℃(x=5∼8). Remanent polarization and coercive field decrease gradually with increasing temperature; both variables have finite values above the Curie point defined by the maximum in the dielectric constant.