• Electrical & Electronic Materials
• /
• v.10 no.2
• /
• pp.156-165
• /
• 1997

D-E hysteresis loops have been measured for the 65/35 mole % copolymer of vinylidene fluoride and trifluoroethylene over wide temperature range. The remanent polarization and the coercive field at room temperature were estimated to be 75 mC/m$^{2}$ and 55 MV/m respectively. D-E hysteresis loops were observed even below the glass transition temperature(-20.deg. C) and the remanent polarization and the coercive field were larger, as the temperature lower. It seems that the remanent polarization and the coercive field depend on the amorphous region as well as crystalline region in this copolymer. And the ferroelectric-to-paraelectric phase transition was observed at 90.deg. C on heating and 80'C on cooling. Double hysteresis loops were observed at the temperature(85.deg. C) of paraelectric phase.

• Electrical & Electronic Materials
• /
• v.11 no.10
• /
• pp.53-59
• /
• 1998

Paraelectric lead landthanum titanate(PLT) thin films have been prepared by a reactive dc magnetron sputtering system using a multicomponent metal target. The surface area control of each element on the target markedly facilitates the fabrication of thin films of complex ceramic compounds. A postdeposition heat-treatment was applied to all as-deposited PLT thin films at annealing temperatures up to 75$0^{\circ}C$ for crystalization. The composition of the PLT(28) thin filmannealed at $650^{\circ}C$ was: Pb, 0.73; La, 0.28; Ti, 0.88; O, 2.9. The dielectric constant and dissipation factor of the thin film(200 nm) at low filed measurements (500 Vcm-1) are 1216 and 0.018, respectively. The charge storage density using a typical Sawyer-Tower circuit with a 500 Hz sine wave was 12.5 $\mu$Ccm-2 at the electric field of 200 kVcm-1.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1995.11a
• /
• pp.80-80
• /
• 1995

• Journal of Advanced Navigation Technology
• /
• v.16 no.6
• /
• pp.1038-1043
• /
• 2012

In this work, a high tunable capacitor using a multi-layer dielectric of BZN/BST/BZN is designed and characterized for reconfigurable RF applications. By utilizing a high tunable BST ferroelectric and a low-loss BZN paraelectric thin film, a multi-layer dielectric of BZN/BST/BZN obtained a tunability of 47 % and $tan{\delta}$ of 0.005. The fabricated tunable capacitor on a quartz wafer using this multi-layer dielectric achieved a Q-factor of 10 and tunability of 60 % at 800 MHz and 15 V. Its size is $327{\times}642{\mu}m2$.

• Journal of the Korean Ceramic Society
• /
• v.32 no.8
• /
• pp.915-921
• /
• 1995

The morphotropic phase boundary and phase transitions of the solid solutiion system, (1-x)(Na1/2Bi1/2)TiO3-PbTiO3＋xPbTiO3 were studied by investigating changes in crystal structure, variations in permittivity with temperature, and calorimetric behavior. It was observed that the morphotropic phase boundary (MPB) of this solid solutiion system was at near 14 mol% of PbTiO3. Compositions containing less than 10mol% PbTiO3 (x<0.1) exhibited a phase transition, i.e. ferroelectric rhombohedrallongrightarrowparaelectric paraelectric cubic, with increasing temperature. Composition containing more than 14 mol% PbTiO3 (x 0.14) showed a phase transition from ferroelectric tetragonal to paraelectric cubic. In the composition range of 0.1$\varepsilon$ (T) curve, which coincided with a phase transition from ferroelectric rhombohedral to an intermediate phase, was also found.

• Electrical & Electronic Materials
• /
• v.9 no.4
• /
• pp.396-403
• /
• 1996

In this paper, the (S $r_{0.85}$.C $a_{0.15}$)Ti $O_{3}$ of paraelectric grain boundary layer (GBL) ceramics were fabricated, and the analysis of microstructuye and the thermally stimulated current(TSC) were investigated for understanding effects of GBL's interfacial phenomenon on variations of electrical properties. As a result, the three peaks of .alpha., .alpha. and .betha. were obtained at the temperature of -20 [.deg. C], 20[.deg. C] and 80[.deg. C], respectively. The origins of these peaks are that the .alpha. peak observed at -20[.deg. C] looks like to be ascribed to the ionization excitation from donor level in the grain, and the .alpha.' peak observed at 20[.deg. C] appears to show up by detrap of the trapped carrier of border between the oxidation layer and the grain, and the .betha. peak observed at 80[.deg. C] seems to be resulted from hopping conduction of existing carrier in the trap site of the border between the oxidation and second phase. and second phase.

• Journal of the Korean Ceramic Society
• /
• v.28 no.12
• /
• pp.969-974
• /
• 1991

The influences of A(Cu1/3Nb2/3)O3(A=Pb, Ba and Sr) on the ferroelectric-paraelectric phase transition of BaTiO3 ceramics has been investigated. The tetragonality of crystal structure decreased with increasing A(Cu1/3Nb2/3)O3 content at room temperature. A linear correlation between Curie point and the tetragonality of lattice was not observed. In all three systems the variation of Curie point with the mole fraction showed similar tendency that the Curie point decreased at lower mole fraction but gradually increased in the region of higher mole fractions, Diffuse phase transitions were observed at higher mole fractions. The variation of Curie points could be explained by internal stress and Jahn-Teller distortion of BO6 due to Cu2+, and it was thought that the diffuse character of phase transition was caused by compositional fluctuation.

• Electrical & Electronic Materials
• /
• v.10 no.2
• /
• pp.97-104
• /
• 1997

In this paper, in order to investigate the behavior of charged particles on (Sr.Ca)TiO$_{3}$ ceramics with paraelectric properties, the characteristics of electrical conduction and thermally stimulated current was measured respectively. As a result, the conduction mechanism is divided into three regions having different mechanism as the current increased. The region I below 200[V/Cm] shows the ohmic conduction. The region B between 200[V/cm] and 2000[V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000[V/cm] is dominated by the tunneling effect. The three peaks of TSC were obtained at the temperature of -20[.deg. C], 20[.deg. C] and 80[.deg. C], respectively. The origins of these peaks are that the .alpha. peak observed at -20[.deg. C] looks like to be ascribed to the ionization excitation from donor level in the grain, and the .alpha.' peak observed at 20 [.deg. C] appears to show up by hopping conduction of the trapped carrier of border between the oxidation layer and the grain, and the .betha. peak observed at 80[.deg. C] seems to be resulted from hopping conduction of existing carrier in the trap site of the border between the oxidation and second phase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.2
• /
• pp.111-120
• /
• 1998

In this paper, the $(SrPb)(CaMg)TiO_3$ ceramics with paraelectric properties were fabricated by the mixed oxide method. It was investigated that which the variation of contents of $Bi_2O_3{\cdot}3TiO_2$ effects on structural, dielectrical and electrical properties of specimens. As a result, the grain size were grown with increasing the contents of $Bi_2O_3{\cdot}3TiO_2$. The relative dielectric constants were increased up to 4[mol%] of $Bi_2O_3{\cdot}3TiO_2$, and decreased more or less at a low temperature in the specimens which had more than. But the temperature coefficient. of capacitance were showed ${\pm}25$[%]. The dielectric loss were less than 0.05 in all specimens which had more than 4[mol%] of $Bi_2O_3{\cdot}3TiO_2$. In order to investigate the behavior of charged particles, the characteristics of electrical conduction were measured. As a result, the conduction current was divided into the three steps as a function of DC electric field. The first step was Ohmic region due to ionic conduction, below 15[kV/cm]. The second step was showed a saturation which seems to be related to a depolarizing field occuring in field-enforced ferroelectric phase, between 15[kV/cm] and 40[kV/cm]. The third step was attributed to Child's law related to space charge which injected from electrode, above 40[kV/cm].

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.30 no.6
• /
• pp.215-219
• /
• 2020

After the specimen of A-site defect double Perovskite La1/3TaO3 single crystal was manufactured, the dielectric properties have been studied between the temperature range of 10 and 800 K. Under 500 K, a paraelectric behavior has been shown, and above 550 K, a dielectric anomaly and a thermal history of dielectric constant has been shown. An activation energy by measurement of ac-conductivity has been the largest with 1.83 eV in the areas below 560 K, 0.35 eV in the areas of 560~690 K, and 0.28 eV in the areas of high temperature above 690 K. From these results, it is assumed that in the areas below 500 K, La3+-ion and vacancy-site are arranged in disorder to maintain a paraelectric phase. And in the areas near 560 K with the highest activation energy, a dielectric anomaly is attributes to rearrangement of La3+-ion due to conduction to vacancy-site or jumping.