Dae-Yong Jeong

Improved Figure of Merit of (Ba,Sr)TiO3-Based Ceramics by Sn Substitution

The dielectric properties of (Ba0.6Sr0.4)(Ti1-xSnx)O3 (0 ≤x ≤0.3) ceramics were investigated. Single-phase specimens having a cubic perovskite structure could be obtained. As Sn concentration increased, dielectric loss decreased untill a composition of x = 0.15 and slightly increased as Sn concentration increased further. The diffused phase transition appeared owing to substitution of Sn ions. When Sn was substituted at 0.1 mol in (Ba0.6Sr0.4)TiO3 at 1400 °C, the dielectric constant, dielectric loss, tunability, Curie point, and figure of merit (FOM) were 1400, 0.0027, 18%, -40 °C, and 67, respectively. These compositions show excellent dielectric properties than those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

Fabrication of an optical grating using high electrostrictive strain polymer as a template

This study introduces a simple and inexpensive method of fabrication of optical microgratings, by using a P(VDF?TrFE?CFE) (that is, poly(vinylidene fluoride?trifluoroethylene)?chlorofluoroethylene) terpolymer with high electrostrictive strain as a template. When an electric field was applied to the terpolymer, which has a patterned electrode, a grating formed on the surface. Epoxy was poured onto the grating of the terpolymer template and cured to produce an optical grating. A 22% efficiency of the first-order diffraction was achieved by fabricating an epoxy micrograting in which the terpolymer template was 13??m thick with electrode/gap/electrode dimensions of 5??m/15??m/5??m.

Phenomenological Analysis of Piezoelectric Properties in 0.88Pb(Zn 1/3 Nb 2/3 )O 3 −0.12PbTiO 3 Single Crystals with an Engineering Domain Configuration

The piezoelectric properties of tetragonal 0.88Pb(Zn ⅓ Nb ⅔ )O₃-0.12PbTiO₃ single crystals are characterized along the 〈111〉 direction, which composed the engineering domain configuration in the tetragonal phase. The 〈111〉-oriented crystal possessed smaller d₃₃ values compared to the crystal along the 〈001〉 spontaneous polarization direction. Based on phenomenological theory, it is shown that the engineering domain configuration does not enhance the piezoelectric constant in tetragonal 0.88Pb(Zn ⅓ Nb ⅔ )O₃-0.12PbTiO₃ single crystals. In addition, the electrostrictive coefficients of Q₁₂=?0.03706 m⁴/C², Q₁₁=0.10765 m⁴/C², and Q₄₄=0.02020 m⁴/C² of tetragonal 0.88PZN-0.12PT single crystals were calculated.

Investigation of piezoelectric ceramic size effect for miniaturing the piezoelectric energy harvester

Energy harvesting from the vibration through the piezoelectric effect has been studied for powering the small wireless sensor nodes. As piezoelectric uni-morph cantilever structure can transfer low vibration to large displacement, this structure was commonly deployed to harvest electric energy from vibrations. Through our previous results, when stress was applied on the cantilever, stress was concentrated on the certain point of the ceramic of the cantilever. In this study, for miniaturing the energy harvester, we investigated how the size of ceramics and the stress distribution in ceramic affects energy harvester characteristics. Even though the area of ceramic was 28.6 % decreased from to , both samples showed almost same maximum power of 0.45 mW and the electro-mechanical coupling factor () of 14 % as well. This result indicated that should be preferentially considered to generate high power with small size energy harvester.

Temperature Dependences of Piezoelectric and Linear Electrooptic Properties of Rhombohedral 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 Single Crystal Oriented in Direction

We characterized the temperature dependences of the linear electrooptical (E-O) and piezoelectric coefficients of the rhombohedral 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals oriented along the direction (the spontaneous polarization direction). The E-O coefficients of the 0.67PMN–0.33PT single crystals were r333=107 pm/V at room temperature and 950 pm/V at 80 °C. The piezoelectric coefficient d311 of the 0.67PMN–0.33PT single crystals increased from 45 pC/N at room temperature to 1015 pC/N at 80 °C. Large E-O and piezoelectric coefficients at 80 °C were from the engineering domain configuration induced by a transition from the rhombohedral phase othorhombic phase.

Improved Dielectric Properties of Low-Temperature-Sintered (Ba,Sr)TiO3-Based Ceramics by Ge Substitution

Multilayer microwave dielectric materials with low sintering temperature are required for microwave phase shifters, filters, and true-time delay devices. We investigated the sintering and dielectric properties of (Ba0.6Sr0.4)(Ti1-xGex)O3 (BSTG; 0.05≤x≤0.3) ceramics. As the Ge concentration was increased, the lattice constant of BSTG ceramics decreased, and Ba2Ge2TiO8, which is the liquid phase at low temperature, was formed. Ba2Ge2TiO8 liquid phase may increase the sintering density. The effect of Ge substitution is the decrease in the sintering temperature from over 1400 to 1150 °C in BST system ferroelectric ceramics. With increasing Ge concentration, the dielectric constant decreased from 2190 to 530, and the dielectric loss decreased up to 0.001 (at 1 MHz) with sintering at 1150 °C for 2 h. When Ge was substituted at 0.05 and 0.1 mol of Ti in the BST at 1150 °C, the dielectric constant, dielectric loss, tunability, Curie temperature, and figure of merit were 2184 and 1529, 0.002 and 0.001, 27 and 23%, -11 and -18 °C, and 135 and 230, respectively. These compositions show microwave dielectric properties comparable to those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are the important materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

DC Bias Effects on Piezoelectric Constants of Rhombohedral Pb(Zn1/3Nb2/3)O3–PbTiO3 Single Crystals

DC bias effects on piezoelectric constants of rhombohedral Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) single crystals were characterized using optical measurements. Piezoelectric constants decreased with increasing DC bias due to a decrease in the dielectric constant. The 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystal, which approximates morphotropic phase boundary (MPB) composition and may have a smaller phase transition energy barrier from rhombohedral to tetragonal, showed a bigger change in piezoelectric constant than the pure PZN and 0.955PZN–0.045PT single crystal, which are far from MPB composition. The different behavior in the piezoelectric constant under DC bias for the composition implies a different domain orientation energy from to or directions.

Characterization of Thermo-optical Properties of Ferroelectric P(VDF-TrFE) Copolymer Using Febry-Perot Interferometer

Phase transition in ferroelectric polymer is very interesting behavior and has been widely studied for real device applications, such as actuators and sensors. Through the phase transition, there is structural change resulting in the change of electrical and optical properties. In this study, we fabricated the Febry-Perot interferometer with the thin film of ferroelectric P(VDF-TrFE) 50/50 mol% copolymer, and thermo-optical properties were investigated. The effective thermo-optical coefficient of P(VDF-TrFE) was obtained as 2.3~3.8 ×10 /K in the ferroelectric temperature region (45 C~65 C) and 6.0×10 /K in the phase transition temperature region (65 C~85 C), which is a larger than optical silica-fiber and PMMA. The resonance transmission peak of P(VDF-TrFE) with the variation of temperature showed hysteretic variation and the phase transition temperature of the polymer in heating condition was higher than in the cooling condition. The elimination of the hysteretic phase transition of P(VDF-TrFE) is necessary for practical applications of optical devices.

Electric Field-Induced Phase Transition Behavior in Tetragonal Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 Single Crystals

Electric field-induced phase transition from the tetragonal to rhombohedral phase was investigated for the 〈111〉 direction in tetragonal PZN-PT single crystals, which have spontaneous polarization along the 〈001〉 direction. From the strain and dielectric data, it was confirmed that the samples followed a tetragonal-orthorhombic-rhombohedral phase transition sequence with application of an electric field. This transition is different from the rhombohedral-tetragonal phase transition of 〈001〉 rhombohedral composition single crystals, in which a phase transition occurred without showing the intermediate orthorhombic phase.