• Transactions on Electrical and Electronic Materials
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• v.16 no.1
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• pp.1-4
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• 2015

(111)-oriented and random oriented $Pb_{0.8}Ba_{0.2}ZrO_3$ (PBZ) perovskite relaxor ferroelectric thin films were fabricated on Pt(111)/$TiO_x$/$SiO_2$/Si substrate by sol-gel method. Nano-scaled antiferroelectric and ferroelectric two-phase coexisted in both (111)-oriented and random oriented PBZ thin film. High dielectric tunability (${\eta}=75%$, E = 560 kV/cm) and figure-of-merit (FOM ~ 236) at room temperature was obtained in (111)-oriented thin film. Meanwhile, giant electrocaloric effect (ECE) (${\Delta}T=45.3K$ and ${\Delta}S=46.9JK^{-1}kg^{-1}$ at $598kVcm^{-1}$) at room temperature (290 K), rather than at its Curie temperature (408 K), was observed in random oriented $Pb_{0.8}Ba_{0.2}ZrO_3$ (PBZ) thin film, which makes it a promising material for the application to cooling systems near room temperature. The giant ECE as well as high dielectric tunability are attributed to the coexistence of AFE and FE phases and field-induced nano-scaled AFE to FE phase transition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.1-7
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• 2021

This study investigated the structural, dielectric, ferroelectric, and strain properties of (0.98-x)Bi1/2Na1/2TiO3-0.02BiFeO3-xSrTiO3 (BNT-BF-100xST, x＝0.20, 0.22, 0.24, 0.26, and 0.28). All samples were successfully synthesized using the conventional solid-state reaction method and sintered at 1,175℃ for 2 h. The average grain size of the BNT-BF-100x ceramics decreased with increasing ST content. Furthermore, we observed that the ferroelectric- relaxor transition temperature (TF-R) decreased with increasing ST content, which eventually vanished in the BNT-BF-24ST ceramics. The results indicated that a ferroelectric to relaxor phase transition could be induced by ST modification. Consequently, a large electromechanical strain of 633 pm/V at 4 kV/mm was observed for the BNT-BF-26ST ceramics. These results imply that our materials have the competitive advantage of larger strain under lower operating field conditions compared with other BNT-based lead-free piezoelectric ceramics. We expect that BNT-BF-ST lead-free piezoelectric ceramics are promising candidates as a novel ternary BNT-based system and can find potential applications in actuators.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.505-512
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• 2023

This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bi-based lead-free ferroelectric/relaxor composites. Bi_1/2Na_0.82K_0.18)_1/2TiO₃ (BNKT) as a ferroelectric material and 0.78Bi_1/2(Na_0.78K_0.22)_1/2TiO₃-0.02LaFeO₃ (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (S_max) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest S_max/E_max value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.

• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.148-155
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• 2008

Dielectric and pyroelectric properties of relaxor ferroelectric in the PMN-PT solid solution series have been investigated. Features of the diffuse phase transition in PMN-PT system, typical relaxor ferroelectric materials, were studied as a function of temperature and frequency. The transition temperature of the ceramics with PT$\sim$0.325 did not depend on the measuring frequency. This can best realized in a relatively random environment that apparently is provided by PMN-rich complex perovskites, including those containing Pb. The composition with PT>0.35 show the characteristics of a normal single phase ferroelectric material. Thus the studies revealed that the morphotropic phase boundary in the PMN-PT system is in the vicinity of PT$\sim$0.3 and it has a small curvature and as a result the compositions near the morphotropic phase boundary show two phase transitions, rhombohedral$\rightarrow$tetragonal$\rightarrow$cubic, when the samples are heated up to higher temperature. The best optimum compositions are observed near the morphotropic phase boundary.

• Smart Structures and Systems
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• v.30 no.3
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• pp.221-237
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• 2022

This paper is concerned with nonlinear modeling and efficient numerical simulation of electrostrictive materials and structures. Two types of such materials are considered: relaxor ferroelectric ceramics and electrostrictive polymers. For ceramics, a geometrically linear formulation is developed, whereas polymers are studied in a geometrically nonlinear regime. In the paper, we focus on constitutive modeling first. For the reversible constitutive response under consideration, we introduce the augmented Helmholtz free energy, which is composed of a purely elastic part, a dielectric part and an augmentation term. For the elastic part, we involve an additive decomposition of the strain tensor into an elastic strain and an electrostrictive eigenstrain, which depends on the polarization of the material. In the geometrically nonlinear case, a corresponding multiplicative decomposition of the deformation gradient tensor replaces the additive strain decomposition used in the geometrically linear formulation. For the dielectric part, we first introduce the internal energy, to which a Legendre transformation is applied to compute the free energy. The augmentation term accounts for the contribution from vacuum to the energy. In our formulation, the augmented free energy depends not only on the strain and the electric field, but also on the polarization and an internal polarization; the latter two are internal variables. With the constitutive framework established, a Finite Element implementation is briefly discussed. We use high-order elements for the discretization of the independent variables, which include also the internal variables and, in case the material is assumed incompressible, the hydrostatic pressure, which is introduced as a Lagrange multiplier. The elements are implemented in the open source code Netgen/NGSolve. Finally, example problems are solved for both, relaxor ferroelectric ceramics and electrostrictive polymers. We focus on thin plate-type structures to show the efficiency of the numerical scheme and its applicability to thin electrostrictive structures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.5
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• pp.516-521
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• 2022

We investigated the microstructure, crystal structure, dielectric, and elecromechanical strain properties of lead-free BaTiO₃ (BT)-modified (Bi_1/2Na_1/2)TiO₃-SrTiO₃ (BNT-ST) piezoelectric ceramics. Samples were prepared by a conventional ceramic processing route. Temperature dependent dielectric properties confirmed that a phase transition from a nonergodic relaxor to an ergodic relaxor was induced when the BT concentration reached 1.5 mol%, interestingly, where the average grain size reached a maximum value of 4.5 ㎛. At the same time, enhanced electromechanical strain (S_max/E_max = 600 pm/V) was obtained. It is suggested that the induced ferroelectric-relaxor phase transition by the BT modification is responsible for the enhancement of electromechanical strain in 1.5 mol% BT-modified BNT-ST ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.523-546
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• 2022

Morphotropic phase boundary (MPB), which is a special boundary that separates two or multiple different phases in the phase diagram of some ferroelectric ceramics, is an important concept in identifying physics that includes piezoelectric responses. MPB, which had not been discovered in organic materials until recently, was discovered in poly(vinylidene fluoride-co-trifluoroethylene (P(VDF-TrFE)), resulting from a molecular approach. The piezoelectric coefficient of P(VDF-TrFE) in this MPB region was achieved up to -63.5 pC N^-1, which is about two times as large as the conventional value of -30 pC N^-1 of P(VDF-TrFE). An order-disorder arrangement greatly affects the rise of the piezoelectric effect and the ferroelectric, paraelectric and relaxor ferroelectric of P(VDF-TrFE), so the arrangement and shape of the polymer chain is important. In this review, we investigate the origin of negative longitudinal piezoelectric coefficients of piezoelectric polymers, which is definitely opposite to those of common piezoelectric ceramics. In addition to the mainly discussed issue about MPB behaviors of ferroelectric polymers, we also introduce the consideration about polymer chirality resulting in relaxor ferroelectric properties. When the physics of ferroelectric polymers is unveiled, we can improve the piezoelectric and pyroelectric properties of ferroelectric polymers and contribute to the development of next-generation sensor, energy, transducer and actuator applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.7
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• pp.562-566
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• 2001

The effects of MnO$_2$ addition on the properties in Pb(Mg$_{1}$3/Nb$_{2}$3/)O$_3$ relaxor ferroelectrics were studied in the phase transition temperature range from -4$0^{\circ}C$ to 11$0^{\circ}C$. Specimens were made via solid state processing method. Dielectric properties, piezoelctric properties, electric-field-induced strain were examined to clarify the effect of MnO$_2$ addition in 0.9MN-0.1PT. As the amount of MnO$_2$ increases, the maximum dielectric constant and the dielectric loss decreases. Q$_{m}$ increased by increasing the doping contents of Mn. When 0.5wt% MnO$_2$ was doped, Q$_{m}$ increased from 95 to 480. The electric-filed-induced strain and polarization decreases as the amount of MnO$_2$ increases. From the experimental results, it was suggested that Mn behaves as an ferroelectric domain pinning element.ent.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.240-243
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• 1999

Piezoelectric properties of O.9PMN-0.1PT relaxor ferroe1ectrics were investigated in the temperature range of $-40^{\circ}C~$100^{\circ}C$. After poled at $-40^{\circ}C$, electro-mechanical properties of the samples were measured by resonance antiresonance method. As the resonance behavior was shown in impedance spectrum obtained below $0^{\circ}C$, it can be c conduded that 0.9PMN-0.1PT is bona-fide ferroelectrics below the phase transition temperature. It is very noteworthy that electro-mechanical resonance occurs at the temperatures far above the phase transition temperature. It is coneluded that ferroelectricity in 0.9PMN-0.1PT relaxor were verified far above the phase transition temperature.

• Journal of Sensor Science and Technology
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• v.23 no.4
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• pp.224-228
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• 2014

The electrocaloric effect of 9/65/35 PLZT thin film fabricated by the sol-gel method, which has not been studied yet, was investigated for its structural, electrical properties as well as temperature change property. The relaxor ferroelectric property of 9/65/35 PLZT thin film was confirmed by examining its dielectric and electrical properties. The relaxor property can cause a more pronounced electrocaloric effect (ECE) in a wider temperature range than normal ferroelectric film. To avoid errors caused by using an indirect measurement method, the leakage current generated by increasing temperatures was minimized by using the optimal maximum electric field ($350kVcm^{-1}$) in the thin film. The largest temperature change ${\delta}T$ (0.23 K) and the electrocaloric strength ${\xi}$ (0.68 mkcm/kV), calculated by equations were obtained. The maximum field change ${\delta}E$ ($191kVcm^{-1}$) was in the vicinity of the curie temperature ($200^{\circ}C$).