Byung-Ik Kim

Piezoelectric Properties and Densification Based on Control of Volatile Mass of Potassium and Sodium in (K0.5Na0.5)NbO3 Ceramics

Recently lead-free ceramic systems have been intensively studied in order to fabricate environmentally friendly piezoelectric ceramics and replace widely used lead-free piezoelectric ceramics. The (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics with non-lead piezoelectric ceramics were manufactured by conventional solid-state synthesis, and we obtained sintered bodies with relative densities over 97.4% by adding excess K (0.44 mol %)/Na (0.22 mol %) to improve sinterability. The composition of the sintered bodies was close to stoichiometric compounds. The electromechanical coupling factor (kp) and piezoelectric constant (d33) of KNN + excess K (0.44 mol %)/Na (0.22 mol %) composition ceramics showed optimal values of 0.341 and 126 pC/N, respectively.

Preparation and Characterization of BCB Resin-BNT Composite Substrate Materials

BCB Resin-BaNd₂Ti₄O₁₂(BNT) composites with BNT contents were prepared by tape casting method and epoxy resin-BNT composites were prepared by using heating press. Their dielectric properties and microstructures were investigated. The dielectric properties such as dielectric constant and dielectric loss at 1㎒ for epoxy resin-BNT composites and BCB resin-BNT composites are improved with an increase of BNT volume fraction. The dielectric constant of the Epoxy-BNT composite increased from 5.9 to 7.8 as the volume fraction of BNT increased from 15 to 25. The dielectric constant of the BCB-BNT composite increased from 9.1 to 15.5 as the volume fraction of BNT increased from 30 to 50. The dielectric behavior of BCB-BNT system can be explained by Lichtenecker’s equation. The dielectric constant of epoxy resin-BNT composite is smaller than that of BCB resin-BNT composite. These results are considered to be related with the dispersion of BNT filler in polymer matrix from the result of SEM photograph.

Non-Stoichiometric Effect in (K,Na)NbO3-Based Perovskite Ceramics

We prepared Li0.04(K0.5Na0.5)x(NbySb0.06)O3 ceramics using the conventional solid-state sintering method and investigated the non-stoichiometric effect on sintering behavior and electrical properties in these material systems. The deficiency of B-site ions gave rise to poor densities, while the densification was improved by adding excess Nb2O5. As the vacancy concentration in the A-site of the perovskite structure increased, the diffuse phase transition was enhanced and the transition temperature (To–t) was lowered. Furthermore, high deficiency in the A-site with x=0.90 and y=0.98 promoted a second phase formation. An increase of alkali cation vacancies led to large remnant polarization and enhanced a pinched hysteresis loop, while the remnant polarization decreased due to a second phase formation. The electro-mechanical coupling factors were significantly influenced by density and second phase formation, not non-stoichiometry, while dielectric constants were influenced by non-stoichiometry, not second phase formation.

Preparation and Characterization of NiZn-Ferrite Nanofibers Fabricated by Electrospinning Process

Electrospinning process is the useful and unique method to produce nanofibers from metal precursor and polymer solution by controlled viscosity. In this study, the NiZn ferrite nanofibers were prepared by electrospinning with a aqueous metal salts/polymer solution that contained polyvinyl pyrrolidone and Fe (Ⅲ) chloride, Ni (Ⅱ) acetate tetrahydrate and zinc acetate dihydrate in N,Ndimethylformamide. The applied electric field and spurting rate for spinning conditions were 10 ㎸, 2 ㎖/h, respectively. The obtained fibers were treated at 250℃ for 1 h to remove the polymer. Finally, the NiZn ferrite fibers were calcined at 600℃ for 3 h and annealed at 900~1200℃ in air. By tuning the viscosity of batch solution before electrospinning, we were able to control the microstructure of NiZn ferrite fiber in the range of 150~500 ㎚ at 770 cP. The primary particle size in 600℃ calcined ferrite fiber was about 10 ㎚. The properties of those NiZn ferrite fibers were determined from X-ray diffraction analysis, electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, thermal analysis, and magnetic measurement.

Practical Application of Simulation Technique for the Resonators Using Piezoelectric Ceramics

In this couple of decades, applications of piezoelectrics to resonators, sensors and actuators have been dramatically accelerated, in addition to the discovery of new materials and devices. Some of the highlights include electrostrictive materials for positioners, ferroelectric single crystals with very high electromechanical couplings for medical transducers, thin/thick films for Micro-Electro-Mechanical Systems starting from a sophisticated chemical technology, and multilayer type actuators fabricated by cofiring technique. All will provide a remarkable industrial impact in the 21st century. Piezoelectric materials exhibit electromechanical coupling, which is useful for the design of devices for oscillating, sensing and actuation. The coupling is exhibited in the fact that piezoelectric materials produce an electrical displacement when a mechanical stress is applied and can produce mechanical strain under the application of an electric field. Due to the fact that the mechanical-to-electrical coupling was discovered first, this property is termed the direct effect, while the electrical-to-mechanical coupling is termed the converse piezoelectric effect. The representative converse piezoelectric effect-applied example is a ceramic resonator. Frequency sources are a key component of much of today’s electronics. Frequency sources are used as sensor, clocks and filters, and the ability to control the accuracy and stability of these devices is vital to their performance characteristics and ability to bring forth advancements in technology. Ceramic resonators stand between quartz crystals and LC/RC oscillators in regard to accuracy. They offer low cost and high reliability timing devices with improved start-up time to quartz crystals. The oscillation of ceramic resonators is dependent upon mechanical resonance associated with their piezoelectric crystal structure. The ceramic resonator oscillates in thickness-shear vibration mode for fundamental frequencies (typical less or equal than 8MHz) and thickness-longitudinal vibration mode for third-overtone mode (above 8MHz to 50MHz). Ceramic resonators have superior resonant impedance than quartz crystal, which offer much better start-up time. They have low cost because of high mass production rate, small size, no need for adjustment. Recently, narrow frequency tolerance characteristics of piezoelectric ceramic resonators have been required for fabricating highly accurate electronic devices. Because of this trend, a low electromechanical coupling coefficient and a high mechanical quality factor have been

(Bi 1/2 Na 1/2 ) 1−x Ca x TiO₃ 세라믹스의 압전 특성 및 상전이 거동

(Bi 1/2 Na 1/2 )TiO3-based ceramics have been intensively studied as lead-free piezoelectric ceramics. In this study, the piezoelectric properties and phase transition behaviors of BNT based solid solution (Bi 0.5 Na 0.5 ) 1?x Ca x TiO₃ (X=0.01~0.25) were investigated. The morphotropic phase boundary(MPB) zone which BNT is transformed from rhombohedral to cubic structure was appeared by adding CaTiO₃ with 0.12 ㏖l by the measurement of permittivity and X-ray diffraction. The behavior which ferroelectric BNT with adding CaTiO₃ was changed to antiferroelectric and paraelectric state was confirmed by the measurement of hysterisis loop and depolarization temperature as a function of temperature. As CaTiO₃ concentration was increased, the phase transition temperature was decreased. The piezoelectric properties were highest at 0.01 ㏖ of CaTiO₃ concentration. The electromechanical coupling factor(Kt) and mechanical quality factor(Qm) were 42% and 254, respectively.

Dielectric and Mechanical Properties of BNT-LCP Composites

We investigated the dielectric and mechanical properties of ceramic polymer composite xBNT - (1-x)LCP (x= 0, 10, 20, 30, 40 vol.%). The disk shaped BNT (BaNd2Ti4O12) - LCP (liquid crystal polymer) composite samples were prepared by compression molding method. With increasing the BNT content in composites from 10 to 40 vol.%, the dielectric constant increased but the dielectric loss as well as bending strength of composites reduced. These composites were well described with modified Lichteneckers model having k = 0.392 and 0.303 for the first and second ball milled BNT filled composites, which means that the BNT filler in composites are well dispersed. The dielectric constant of the composite comprised of the second milled BNT (D50 = 1.39 um) was higher that of the composite of the first milled BNT (D50= 2.45 um), which seems to be related with the different particle size and dispersion of BNT fillers in LCP matrix. The bending strength of the composite containing the second milled BNT was superior to that of the composite of the first milled BNT.

Electrical properties and microstructure of microwave dielectric ceramics (Ca 0.7 Sr 0.3 ) m (Ti y Zr 1-y )O 3

The effects of mole ratio(A/B) m and Ti-ion on the dielectric properties and microstructure of the microwave dielectric ceramics were investigated. Ti ions substituted on Zr-sites in these modified composition strongly affect the sintering density and microstructure of the fired ceramic body. With increasing the amount of Ti substituted on Zr-sites, the sintered density rapidly increased and the dense microstructure was obtained for the compositions having mole ratio of 1.01, whereas the sintered density and microstructure are nearly constant with the content of Ti-ion for the compositions having mole ratio of 0.99. With increasing the content of Ti ion, the curve of TCC (Temperature Coefficient of Capacitance) as a function of temperature rotated clockwise and satisfied the COG characteristics for both of compositions with mole ratio of 0.99 and 1.01. The content of Ti ion seems to be more effective than mole with respect to the controlling of firing and TCC.

Microstructures and Magnetic Properties of Multiferroic BiFeO 3 Thin Films Deposited by RF Magnetron Sputtering Method

(BFO) thin films were deposited on Pt/Ti//Si(100) substrates by RF magnetron sputtering method at room temperature. The influence of the flow rate of gas on the preparation of thin films was studied. XRD results indicate that the thin films were crystallized to the perovskite structure with the presence of small amount of impurity phases. The flow rate of gas has great affect on the microstructures and magnetic properties of thin films. As flow rate of gas increased, roughness and grain size of the thin films increased. thin films exhibited weak ferromagnetic behavior at room temperature. The PFM images revealed correlation between the surface morphology and the piezoresponse, indicating that the piezoelectric coefficient is related to microstructure.

The spurious vibration analysis of ceramic resonator using 3 rd overtone vibration

Various vibration modes used in ceramic resonators which have been commercialized recently, and they have been mainly used in generating frequencies greater than 10 MHz with the 3rd overtone vibration (TE3 mode vibration) and 2nd vibration (TE2 mode vibration) generated by laminating two layers. In the case of the TE2 mode vibration, it is known there is no problem of a spurious response generated in the TE3 mode vibration. In this study, the TE3 mode vibration and TE2 mode vibration of PbTiO3-based ceramics were simulated by the FEMLAB program and compared the results, which simulation revealed that the TE2 mode generated vibration in a more local area than TE3 mode. We tried to investigate the origin of the spurious response in TE3 mode vibration by analyzing the influences of the ratio of electrode overlap length (L) per thickness (T) of resonators. It was found that the anti-resonant frequency of a TE3 vibration and the resonant frequency of a spurious vibration became closer to split impedance shape with increasing the electrode overlap length, and the resonant impedance of TE3 vibration became unstable in short overlap length. It was expected that the TE3 mode would be less influenced by spurious vibrations in a L/T ratio of 2.0 ~3.0 in a manufactured resonator.