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Electrospinning법으로 제조된 PZT 섬유의 구조분석 및 특성평가
박춘길,윤지선,정영훈,남중희,조정호,백종후,정대용,Park, Chun Kil,Yun, Ji Sun,Jeong, Young Hun,Nam, Joong-Hee,Cho, Jeong Ho,Paik, Jong-Hoo,Jeong, Dae Young 한국세라믹학회 2013 한국세라믹학회지 Vol.50 No.6
Currently, piezoelectric ceramics are being applied in various fields, such as ultrasonic sensors, vibration devices, sound filters, and various energy conversion devices. Flexible piezoelectric ceramics are widely studied in an effort to mitigate the disadvantages of their brittle and inductile properties. Structural damage to piezoelectric fibers is much less than that to thin films when piezoelectric fibers are twisted or bent. Therefore, stretchable devices can be fabricated if piezoelectric fibers are obtained using an elongated substrate. In this study, sintering processes of PZT ($Pb(Zr_{0.53}Ti_{0.47})O_3$) fibers prepared by electrospinning were optimized through the TGA and XRD analyses. The crystal structure and microstructure of the piezoelectric fibers were investigated by XRD, FE-SEM and TEM.
박춘길,임지호,박정수,Park, Chun-Kil,Lim, Ji-Ho,Park, Jung-Soo 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.3
$(1-x)Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3-xLaFeO_3$ ceramics were fabricated using a solid state reaction method. The microstructural, ferroelectric and piezoelectric properties were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and polarization hysteresis loops (P-E). XRD results indicated that BNKT ceramic crystal structure modified by $LaFeO_3$ was transformed from a ferroelectric tetragonal to a non-polar pesudo-cubic phase with increased $LaFeO_3$ content. The improved piezoelectric properties resulted from the addition of $LaFeO_3$ up to 3 mol%. The $LaFeO_3$ 3mol% sample showed markedly improved piezoelectric and strain behaviors in comparison with pure BNKT ceramic.
박춘길,윤지선,조정호,백종후,정영훈,정대용,Park, Chun Kil,Yun, Ji Sun,Cho, Jeong Ho,Paik, Jong-Hoo,Jeong, Young Hun,Jeong, Dae young 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.6
PZT($Pb(Zr_{0.53}Ti_{0.47})O_3$)/PVDF(poly vinylidene fluoride) nanofibers were prepared based on DMF (dimethylformamide) and acetone solvent by electrospinning. The optimum concentration of a PZT and PVDF composite solution for the formation of nanofibers was found by SEM (scanning electron microscopy) observations. XRD (X-ray diffraction) measurements indicated that the characteristics of PZT and PVDF coexisted. The effects of the PZT concentration on the tensile strength were investigated.
에어로졸 증착법에 의해 제조된 PZT 막의 상변화와 전기적 특성
박춘길,강동균,이승희,공영민,정대용,Park, Chun-Kil,Kang, Dong-Kyun,Lee, Seung-Hee,Kong, Young-Min,Jeong, Dae-Yong 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.9
$Pb(Zr_{0.52}Ti_{0.48})O_3$ (PZT) films with a thickness of $5{\sim}10{\mu}m$ at the morphotropic phase boundary were fabricated by aerosol-deposition (AD), and their phase evolution and electrical properties were investigated. The microstructure of the AD PZT films revealed nanosized grains with a low crystallinity and a dense structure at room temperature. The AD PZT films showed a mixture of tetragonal and rhombohedral phases. The post-annealing temperature was varied to study the phase transition behavior. The crystallinity of the AD PZT films was enhanced by annealing at 450, 550, and $650^{\circ}C$ for 2 h. At $650^{\circ}C$, the tetragonal and rhombohedral phases reacted to form a bridge phase between the two phases. The polarization-electric field hysteresis loops of the AD PZT film annealed at $650^{\circ}C$ exhibited a smaller cohesive field and a lower slim hysteresis than the films annealed at 450 and $550^{\circ}C$.
과 액상 형성에 의한 비납계 압전 (Na,K)NbO<sub>3</sub>-Ba(Cu,Nb)O<sub>3</sub> 결정립의 비정상 성장 거동 및 전기적 특성
임지호,이주승,이승희,정한보,박춘길,안철우,유일열,조경훈,정대용,Lim, Ji-Ho,Lee, Ju-Seung,Lee, SeungHee,Jung, Han-Bo,Park, Chun-kil,Ahn, Cheol-Woo,Yoo, Il-Ryeol,Cho, Kyung-Hoon,Jeong, Dae-Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.4
$Pb(Zr,Ti)O_3$ (PZT) is used for the various piezoelectric devices owing to its high piezoelectric properties. However, lead (Pb), which is contained in PZT, causes various environment contaminations. $(K,Na)NbO_3$ (NKN) is the most well-known candidate for a lead-free composition to replace PZT. A single crystal has excellent piezoelectric-properties and its properties can be changed by changing the orientation direction. It is hard to fabricate a NKN single crystal due to the sodium and potassium. Thus, $(Na,K)NbO_3-Ba(Cu,Nb)O_3$ (NKN-BCuN) is chosen to fabricate the single crystal with relative ease. NKN-BCuN pellets consist of two parts, yellow single crystals and gray poly-crystals that contain copper. The area that has a large amount of copper particles may melt at low temperature but not the other areas. The liquid phase may be responsible for the abnormal grain growth in NKN-BCuN ceramics. The dielectric constant and tan ${\delta}$ are measured to be 684 and 0.036 at 1 kHz in NKN-BCuN, respectively. The coercive field and remnant polarization are 14 kV/cm and $20{\mu}C/cm^2$.
상온분말분사법에 의해 Yttria Stabilized Zirconia 코팅된 STS304 표면 경도 특성
임지호 ( Ji-ho Lim ),박춘길 ( Chun-kil Park ),이용석 ( Yong-seok Lee ),공영민 ( Young-min Kong ),강권호 ( Kweon Ho Kang ),김형순 ( Hyung Sun Kim ),정대용 ( Dea-yong Jeong ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.3
To improve the surface harndess of the STS304, Yttria stabilized zirconia (YSZ) films with nano-sized grain were deposited by an aerosol-deposition (AD) method. Coating layers showed dense structure and had ~5μm thickness. When 3 mol% YSZ powders with tetragonal phase were deposited on STS304 substrate, tetragonal structure was transformed to cubic structure due to the high impact energy during the AD process. At the same time, strong impact by YSZ particles allowed the austenite phase in STS304 to be transformed into martensite phase. Surface hardness measured with nano indentor showed that YSZ coated film had 11.5 GPa, which is larger value than 7 GPa of STS304.
절연파괴특성 향상을 위한 나노미세구조 (Ba<sub>0.7</sub>Ca<sub>0.3</sub>)TiO<sub>3</sub> 후막 제조 및 에너지 저장 특성 평가
이주승,윤송현,임지호,박춘길,류정호,정대용,Lee, Ju-Seung,Yoon, Songhyeon,Lim, Ji-Ho,Park, Chun-Kil,Ryu, Jungho,Jeong, Dae-Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.2
Lead free $(Ba_{0.7}Ca_{0.3})TiO_3$ thick films with nano-sized grains are prepared using an aerosol deposition (AD) method at room temperature. The crystallinity of the AD thick films is enhanced by a post annealing process. Contrary to the sharp phase transition of bulk ceramics that has been reported, AD films show broad phase transition behaviors due to the nano-sized grains. The polarization-electric hysteresis loop of annealed AD film shows ferroelectric behaviors. With an increase in annealing temperature, the saturation polarization increases because of an increase in crystallinity. However, the remnant polarization and cohesive field are not affected by the annealing temperature. BCT AD thick films annealed at $700^{\circ}C/2h$ have an energy density of $1.84J/cm^3$ and a charge-discharge efficiency of 69.9 %, which is much higher than those of bulk ceramic with the same composition. The higher energy storage properties are likely due to the increase in the breakdown field from a large number of grain boundaries of nano-sized grains.
상온분말분사공정을 이용한 고밀도 폴리머-세라믹 혼합 코팅층 제조 및 에너지 저장 특성 향상
임지호,김진우,이승희,박춘길,류정호,최두현,정대용,Lim, Ji-Ho,Kim, Jin-Woo,Lee, Seung Hee,Park, Chun-kil,Ryu, Jungho,Choi, Doo hyun,Jeong, Dae-Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.3
This study examines paraelectric $Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7$ (BZN), which has no hysteresis and high dielectric strength, for energy density capacitor applications. To increase the breakdown dielectric strength of the BZN film further, poly(vinylidene fluoride) BZN-PVDF composite film is fabricated by aerosol deposition. The volume ratio of each composition is calculated using dielectric constant of each composition, and we find that it was 12:88 vol% (BZN:PVDF). To modulate the structure and dielectric properties of the ferroelectric polymer PVDF, the composite film is heat-treated at $200^{\circ}C$ for 5 and 30 minutes following quenching. The amount of ${\alpha}-phase$ in the PVDF increases with an increasing annealing time, which in turn decreases the dielectric constant and dielectric loss. The breakdown dielectric strength of the BZN film increases by mixing PVDF. However, the breakdown field decreases with an increasing annealing time. The BZN-PVDF composite film has the energy density of $4.9J/cm^3$, which is larger than that of the pure BZN film of $3.6J/cm^3$.
상온분사분말공정에 의해 SrTiO<sub>3</sub> (100), (110) Seed에 코팅된 BaTiO<sub>3</sub>의 고온 성장 거동 분석
임지호,이승희,김기현,지성엽,정승운,박춘길,정한보,정대용,Lim, Ji-Ho,Lee, Seung Hee,Kim, Ki Hyun,Ji, Sung-Yub,Jung, Suengwoon,Park, Chun-kil,Jung, Han-Bo,Jeong, Dae-Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.11
Single crystals, which have complexed composition, are fabricated by solid state grain growth. However, it is hard to achieve stable properties in a single crystal due to trapped pores. Aerosol deposition (AD) is suitable for fabrication of single crystals with stable properties because this process can make a high density coating layer. Because of their unique features (nano sized grains, stress inner site), it is hard to fabricate single crystals, and so studies of grain growth behavior of AD film are essential. In this study, a $BaTiO_3$ coating layer with ${\sim}9{\mu}m$ thickness is fabricated using an aerosol deposition method on (100) and (110) cut $SrTiO_3$ single crystal substrates, which are adopted as seeds for grain growth. Each specimen is heat-treated at various conditions (900, 1,100, and $1,300^{\circ}C$ for 5 h). $BaTiO_3$ layer shows different growth behavior and X-ray diffraction depending on cutting direction of $SrTiO_3$ seed. Rectangular pillars at $SrTiO_3$ (100) and laminating thin plates at $SrTiO_3$ (110), respectively, are observed.