• 한국재료학회지
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• 제30권9호
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• pp.480-488
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• 2020

The electrocaloric effect can be observed in pyroelectric materials based on conversion between electrical and thermal energy, and can be utilized for the future environment-friendly refrigeration technology. Especially, a strong electrocaloric effect is expected in materials in which field-induced phase transition can be achieved. Emerging fluorite-structure ferroelectrics such as doped hafnia and zirconia, first discovered in 2011, are considered the most promising materials for next-generation semiconductor devices. Besides application of fluorite-structure ferroelectrics for semiconductor devices based on their scalability and CMOS-compatibility, field-induced phase transition has been suggested as another interesting phenomenon for various energy-related applications such as solid-state cooling with electrocaloric effect as well as energy conversion/storage and IR/piezoelectric sensors. Especially, their giant electrocaloric effect is considered promising for solid-state-cooling. However, the electrocaloric effect of fluorite-structure oxides based on field-induced phase transition has not been reviewed to date. In this review, therefore, the electrocaloric effect accompanied by field-induced phase transition in fluorite-structure ferroelectrics is comprehensively reviewed from fundamentals to potential applications.

• 한국재료학회지
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• 제22권1호
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• pp.35-41
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• 2012

Presently, the most promising family of lead-free piezoelectric ceramics is based on $K_{0.5}Na_{0.5}NbO_3$(KNN). Lithium, silver and antimony co-doped KNN ceramics show high piezoelectric properties at room temperature, but often suffer from abnormal grain growth. In the present work, the $(Ba_{0.85}Ca_{0.15})(Ti_{0.88}Zr_{0.12})O_3$ component, which has relaxor ferroelectric characteristics, was doped to suppress the abnormal grain growth. To investigate this effect, Lead-Free $0.95(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}NbO_3-(0.05-x)AgSbO_3-x(Ba_{0.85}Ca_{0.15})(Ti_{0.88}Zr_{0.12})O_3$[KNLN-AS-xBCTZ] piezoelectric ceramics were synthesized by ball mill and nanosized-milling processes in lead-Free $0.95(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}NbO_3-(0.05-x)AgSbO_3$ in order to suppress the abnormal grain growth. The nanosized milling process of calcined powders enhanced the sintering density. The phase structure, microstructure, and ferroelectric and piezoelectric properties of the KNLN-AS ceramics were systematically investigated. XRD patterns for the doped and undoped samples showed perovskite phase while tetragonality was increased with increasing BCZT content, which increase was closely related to the decrease of TO-T. Dense and uniform microstructures were observed for all of the doped BCZT ceramics. After the addition of BCTZ, the tetragonal-cubic and orthorhombic-tetragonal phase transitions shifted to lower temperatures compared to those for the pure KNNL-AS. A coexistence of the orthorhombic and tetragonal phases was hence formed in the ceramics with x = 0.02 mol at room temperature, leading to a significant enhancement of the piezoelectric properties. For the composition with x = 0.02 mol, the piezoelectric properties showed optimum values of: $d_{33}$ = 185 pC/N, $k_P$ = 41%, $T_C=325^{\circ}C$, $T_{O-T}=-4^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 센서 박막재료 반도체재료 기술교육
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• pp.78-81
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• 2002

Ferroelectric thin film is a very attractive material for the tunable microwave device applications such as electronically tunable mixers, delay lines, filters and phase shifters. Thin films of $Pb_{x}Sr_{1-x}TiO3(PST)$ were fabricated onto Pt/Ti/SiO2/Si substrate by the sol-gel method. We have investigated the structural and dielectric properties of PST(50/50) thin films for tunable microwave device applications. The PST thin films show typical polycrystalline structure with a dense microstructure without secondary phase formation. Dielectric properties of PST films are strongly dependent on annealing temperature. The dielectric constants, loss and tunability of the PST (50/50) thin films were 404, 0.023 and 51.73 %, respectively.

• 한국세라믹학회지
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• 제31권2호
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• pp.171-176
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• 1994

The spin-casted PLZT(9/65/35) thin films through polymeric sol-gel process were prepared on Pt substrate. The crack-free, uniform and dense films were obtained by post-annealing at the temperature between 35$0^{\circ}C$ and $700^{\circ}C$. The composite structure mixed together with large grains called "rosette" and surrounding small grains were observed on the films annealed over $600^{\circ}C$. Pyrochlore phase was completely changed to perovskite phase above $600^{\circ}C$ with the increase of annealing temperature. Dielectric constant (k) was larger with the increase of film thickness and annealing temperature. from the measurements of dielectric constant as a function of measuring temperature, it was also observed that Curie temperature was shifted to higher temperature with the increase of film thickness and annealing temperature. The pyroelectric coefficient(P) of 10 times coated film annealed at $700^{\circ}C$ was 65 $\mu$C/$\textrm{cm}^2$.K.$.K.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1261-1267
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• 2000

외부에서 자극이 가해질 때 상전이(phase transformations)하는 방식으로 대응하는 재료들이 최근 다양하게 연구되고 있다. 예를 들어 형상기억합금은 주변 온도의 변화에 대응하여 그 형상을 변화시키는데 이 과정은 미시적으로는 격자의 형태가 - 예를 들면 정방형 격자에서 입방형격자로 혹은 그 반대로 - 변화하는 과정이다. 강유전체 역시 외부에서 인가되는 전계의 변화에 대응하여 그 격자구조가 변하는데 그와 함께 기계적 변형이 동반하게 된다. 본 논문에서는 상전이를 하는 재료에 적용될 수 있는 1차원 구성방정식을 강유전체의 예를 들어 제시하고 간단한 계산결과를 보이기로 한다. 본 모델을 확장하여 강유전체에서의 분극역전(polarization reversals)에 대한 3차원 유한요소 모델을 개발하고 응용하려는 시도가 이루어지고 있다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.I
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• pp.399-402
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• 2005

We have studied the Pixel Isolated Phase Separated Composite Organic Film (PI-PSCOF). The PI-PSCOF can be made by the anisotropic phase separation between Ferroelectric Liquid Crystals and Pre-polymer materials by irradiating the UV with optimizing its intensity and time. In the technology, the FLC molecules are isolated in pixels where FLCs are surrounded by the inter-pixel vertical polymer walls and the horizontal polymer films on the upper substrate. The good merits of this technology are fast response time, and good mechanical and thermal stability against external high pressure and temperature. We will compare the results obtained from FLC, PSCOF, and PI-PSCOF modes by using the electro-optic measurement and x-ray scattering, and mechanical method. We believe that the PI-PSCOF technology can be a best candidate for future Flexible Display Applications.

• 한국세라믹학회지
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• 제26권6호
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• pp.755-762
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• 1989

A pyroelectric ceramic material based on Pb(Sn1/2Sb1/2)O3 modified PZT system is studied as a function of the amount of Pb(Sn1/2Sb1/2)O3 and PbTiO3. With increasing the Pb(Sn1/2Sb1/2)O3 amount the dielectric constant increases up to 10mol% and then decreases, but the pyroelectric coefficient decreases and as the PbTiO3 contents increase in the 10mol% added PZT system, the dielectric constant increases but the infrared sensitivity decreases. The good pyroelectric material has low dielectric constant and no pyrochlore phase, but does not depend in the amount of remanent dipole, and its composition sites around ferroelectric-to-antiferroelectric phase boundary.

• 한국세라믹학회지
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• 제34권6호
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• pp.569-576
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• 1997

Electrically-induced strain and polarization studies of the (1-x)Pb(Mg1/3Nb2/3)O3-PbZrO3 crystalline solutions have been done. Dielectric constants with temperature were investigated for 0$\leq$x$\leq$0.95. With increasing PbZrO3 content the transition maxima were found to move to higher temperature region and DPT (Diffused Phase Transition) properties were decreased for x$\leq$0.60. Phase transition between ferroelectric states and antiferroelectric states was confirmed for 0.93$\times$10-3 for 0.4

• 한국세라믹학회지
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• 제43권11호
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• pp.680-687
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• 2006

An overview is given to optimize the solid state processes toward phase pure and well-crystallized fine particulates of mixed oxides, serving as electroceramic materials in various genres. Elevation of the reactivity and preservation of stoichiometry of the starting mixture are of universal importance. Mechanical activation is versatile for these purposes, particularly when an oxygen atom as a hinge promotes formation of hetero-bridging bonds between dissimilar cationic species prior to calcination. Case studies carried out recently in the author's laboratory are displayed and compared for ferroelectric materials, i.e. $PbMg_{1/3}Nb_{2/3}O_3$ $xPbTiO_3$(PMN-PT), $(1-y)Pb(Zn_xMg{1-x})_{1/3}$ $yNb_{2/3}O_3$ (PZN-PMN), $BaBi_2Ta_2O_9$ (BBT), $Ba(Mg_{1/3}Ta_{2/3})O_3$ (BMT), and ferromagnetics, i.e. M-, Y-, and Z-phases of Ba-hexaferrites.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.311-314
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• 1999

Ferroelectric PZT heterolayered thin films were fabricated by spin coating method on the Pt/Ti/SiO$_2$/Si substrate using PZT(10/90) and PZT(90/10) metal alkoxide solutions. All PZT heterolayered films showed a homogeneous grain structure without presence of the rosette structure. It can be assumed that the lower PZT layers a role of nucleation site or seeding layer for the formation of the upper PZT layer. Zr and Ti diffusion into the Pt electrode were mainly distributed at the surface of Pt electrode beneath the PZT/Pt interface. The PZT/Pt interfacial layer showed a microstructure characterized by a grain phase surrounded by a Pb-deficient pyrochlore matrix phase. The relative dielectric constant and the dielectric loss of the PZT-6 film were 567 and 3.6, respectively.