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Koji Yamada - One of the best experts on this subject based on the ideXlab platform.
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Grain Size Effect on the giant dielectric constant of cacu3ti4o12 nanoceramics prepared by mechanosynthesis and spark plasma sintering
Journal of Applied Physics, 2014Co-Authors: Mohamad M Ahmad, Koji YamadaAbstract:In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive Grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The...
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Grain Size Effect on the giant dielectric constant of cacu3ti4o12 nanoceramics prepared by mechanosynthesis and spark plasma sintering
Journal of Applied Physics, 2014Co-Authors: Mohamad M Ahmad, Koji YamadaAbstract:In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive Grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.
D A Payne - One of the best experts on this subject based on the ideXlab platform.
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the role of interfaces on an apparent Grain Size Effect on the dielectric properties for ferroelectric barium titanate ceramics
Ferroelectrics, 1998Co-Authors: M H Frey, P Han, D A PayneAbstract:Abstract We report the Effect of interfaces (and thus internal surface area Effects) on the value of dielectric constant (K′) calculated from capacitance and geometry data for sub-micron barium titanate (BaTiO3) ceramics prepared with decreasing Grain Size (and Grain volumes). A series model is proposed to explain the decreasing values of apparent K′ obtained for Grain Sizes below 0.5 μm. A distinction is made between the true dielectric constant (K′) and the apparent dielectric constant (K′) calculated from experimental data. The progressive suppression in K′ is explained in terms of ferroelectric Grains of constant dielectric constant (K′1) separated by a lower-K 2 boundary region (i.e., Grain boundary) of constant thickness (d 2). The problem is one of an increasing interfacial surface area to Grain volume ratio in fine-Grain dielectrics. We begin by reporting original dielectric data for high pressure-densified ultrafine-Grain BaTiO3 ceramics. Chemically prepared BaTiO3 powder was consolidated at high...
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Grain Size Effect on structure and phase transformations for barium titanate
Physical Review B, 1996Co-Authors: M H Frey, D A PayneAbstract:We report the results of an investigation into the Grain-Size dependence of lattice structure for barium titanate (${\mathrm{BaTiO}}_{3}$) ceramics prepared by a sol-gel method. Raman and infrared spectroscopy, x-ray diffraction, and differential scanning calorimetry were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with heat treatment and Grain growth from the nano scale to the micron scale for ${\mathrm{BaTiO}}_{3}$ polycrystals. Raman spectroscopy and optical second-harmonic-generation measurements indicated the onset of local room-temperature acentric crystal symmetry with heat treatment and crystallite growth, well before the observation of any tetragonal structure by x-ray diffraction. Analysis of the room-temperature Raman spectra for ultrafine Grain (Grain Size 0.1 \ensuremath{\mu}m) polycrystals suggested that a locally orthorhombic structure preceded the globally tetragonal form with Grain growth. In support of this observation, differential scanning calorimetry suggested the orthorhombic-tetragonal phase transformation shifts up through room temperature with decreasing Grain Size. Hot-stage transmission electron microscopy studies revealed that fine Grain (Grain Size \ensuremath{\approxeq}0.1 \ensuremath{\mu}m) ceramics, which showed a thermal anomaly associated with the cubic-tetragonal phase transformation, were untwinned at room temperature, as well as on cycling through the normal Curie temperature, suggesting a single-domain state for individual Grains. The findings are discussed in light of a number of possible causes, including the presence of processing-related hydroxyl defects and the Effect of elastic constraints on phase transformation behavior for ${\mathrm{BaTiO}}_{3}$ Grains in a polycrystalline microstructure. \textcopyright{} 1996 The American Physical Society.
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Grain Size Effect on structure and phase transformations for barium titanate
Physical Review B, 1996Co-Authors: M H Frey, D A PayneAbstract:We report the results of an investigation into the Grain-Size dependence of lattice structure for barium titanate (BaTiO{sub 3}) ceramics prepared by a sol-gel method. Raman and infrared spectroscopy, x-ray diffraction, and differential scanning calorimetry were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with heat treatment and Grain growth from the nano scale to the micron scale for BaTiO{sub 3} polycrystals. Raman spectroscopy and optical second-harmonic-generation measurements indicated the onset of local room-temperature acentric crystal symmetry with heat treatment and crystallite growth, well before the observation of any tetragonal structure by x-ray diffraction. Analysis of the room-temperature Raman spectra for ultrafine Grain (Grain Size {lt}0.1 {mu}m) polycrystals suggested that a locally orthorhombic structure preceded the globally tetragonal form with Grain growth. In support of this observation, differential scanning calorimetry suggested the orthorhombic-tetragonal phase transformation shifts up through room temperature with decreasing Grain Size. Hot-stage transmission electron microscopy studies revealed that fine Grain (Grain Size {approx_equal}0.1 {mu}m) ceramics, which showed a thermal anomaly associated with the cubic-tetragonal phase transformation, were untwinned at room temperature, as well as on cycling through the normal Curie temperature, suggesting a single-domain state for individual Grains.more » The findings are discussed in light of a number of possible causes, including the presence of processing-related hydroxyl defects and the Effect of elastic constraints on phase transformation behavior for BaTiO{sub 3} Grains in a polycrystalline microstructure. {copyright} {ital 1996 The American Physical Society.}« less
Mohamad M Ahmad - One of the best experts on this subject based on the ideXlab platform.
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Grain Size Effect on the giant dielectric constant of cacu3ti4o12 nanoceramics prepared by mechanosynthesis and spark plasma sintering
Journal of Applied Physics, 2014Co-Authors: Mohamad M Ahmad, Koji YamadaAbstract:In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive Grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The...
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Grain Size Effect on the giant dielectric constant of cacu3ti4o12 nanoceramics prepared by mechanosynthesis and spark plasma sintering
Journal of Applied Physics, 2014Co-Authors: Mohamad M Ahmad, Koji YamadaAbstract:In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different Grain Sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosyntheSized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The Grain Size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-Sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the Grain Size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-Sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive Grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.
Xiaohui Wang - One of the best experts on this subject based on the ideXlab platform.
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Grain Size Effect and microstructure influence on the energy storage properties of fine Grained batio3 based ceramics
Journal of the American Ceramic Society, 2017Co-Authors: Baibo Liu, Xiaohui Wang, Ruoxi ZhangAbstract:The dependence of energy storage properties on Grain Size was investigated in BaTiO3-based ferroelectric ceramics. Modified BaTiO3 ceramics with different Grain Size were fabricated by two-step sintering method from BaTiO3 powders doped with Al2O3 and SiO2 by aqueous chemical coating. For samples doped with ZnO sintering aid in addition to Al2O3-SiO2, the density and breakdown strength increased significantly. In general, samples with smaller Grains have lower polarization but higher energy storage efficiency. Al2O3-SiO2-ZnO-doped samples with average Grain Size of 118±2 nm have an energy density of 0.83±0.04 J/cm3. Obvious segregation of doping elements in second phase and Grain boundary was observed by TEM-EDS. Impedance spectroscopy further explains the relationship between microstructure and properties. Compared to common energy storage ceramics, the Grain Size of this low-cost ceramics sintered at relatively low temperature is small, and the pilot scale production has been well completed. All these features make the utilization in multilayer devices and industrial mass production possible. In addition, the obtained rules are helpful in further development of energy storage ceramics.
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Grain Size Effect on electrical and reliability characteristics of modified fine Grained batio3 ceramics for mlccs
Journal of The European Ceramic Society, 2014Co-Authors: Huiling Gong, Xiaohui Wang, Shaopeng Zhang, Hai WenAbstract:Abstract Fine-Grained BaTiO3-based ceramics of different Grain Sizes (118–462 nm) with core–shell structures were prepared by a chemical coating method, having good dielectric properties and gentle temperature stability. The Grain Size Effect on the dielectric properties and insulation resistivity of modified fine-Grained BaTiO3 ceramics under high temperatures and electric fields were investigated. The DC bias shows a strong Effect on the dielectric properties with decreasing Grain Size. In the finest ceramics, the absolute value of the capacitance stability factor was the smallest, indicating that the modified-BaTiO3 ceramic capacitor with smaller Grains had higher reliability under the DC bias voltage. The highly accelerated lifetime test results showed that with decreasing the Grain Size, samples exhibited higher insulation resistance under elevated temperatures and high voltages. Impedance analysis proved that the finer-Grained ceramic with core–shell structure had higher activation energy for both Grain and Grain boundary, whereas the proportion of ionic conductivity was lower.
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Grain Size Effect on piezoelectric and ferroelectric properties of batio3 ceramics
Journal of The European Ceramic Society, 2014Co-Authors: Yu Huan, Xiaohui Wang, Jian Fang, Longtu LiAbstract:Abstract A series of dense barium titanate (BaTiO 3 , BTO) ceramics with different Grain Sizes (GS) were prepared by two-step sintering method. The Effect of GS on piezoelectric coefficient ( d 33 ) and planar electromechanical coupling factor ( k p ) displayed a trend similar to that on relative permittivity ( ɛ ′). The values of d 33 , k p , and ɛ ′ increased significantly with decreasing GS, reaching maximum values ( ɛ ′ = 6079, d 33 = 519 pC/N and k p = 39.5%) at approximately 1 μm, and then decreased rapidly with further decreasing GS. The results revealed that high-performance BTO ceramics could be Effectively prepared by controlling GS. Polarization–electric field hysteresis loops and temperature dependence of ɛ′ were also investigated.
Y T Zhu - One of the best experts on this subject based on the ideXlab platform.
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Grain Size Effect on tensile properties and slip systems of pure magnesium
Acta Materialia, 2021Co-Authors: Kang Wei, Y T Zhu, Yonghao Zhao, Yang Cao, D D Yin, Lirong Xiao, Song Pang, Hao ZhouAbstract:Abstract Grain refinement can significantly enhance the strength of metallic materials, but usually at the sacrifice of ductility. Here we report that refinement of magnesium Grains can not only improve its strength, but also its ductility, due to the activation of more slip systems. It is found that pure Mg with coarse Grain Size ( d ¯ =125 μm) has a low ductility and uniform elongation (5.3%), due to the limited basal slip systems. In contrast, fine-Grained Mg ( d ¯ =5.5 μm) exhibits enhanced work hardening and ductility as well as uniform elongation (18.3%). Two beam condition TEM analysis revealed that the improved properties were due to the activation of non-basal dislocations, such as and dislocations with reducing the Grain Sizes. It is also found that the dislocations are unstable and can dissociate into either and dislocations or I1 stacking faults. Contributions of nano stacking faults on strengthening and ductilization as well as their formation mechanism are rationalized and discussed.
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Grain Size Effect on deformation twin thickness in a nanocrystalline metal with low stacking fault energy
Journal of Materials Research, 2019Co-Authors: Liangjuan Dai, Yonghao Zhao, Yang Cao, Y T ZhuAbstract:Grain Size Effect on twin thickness has been rarely investigated, especially when the Grain Size is less than 1000 nm. In our previous work (Mater. Sci. Eng. A527, 3942, 2010), different severe plastic deformation techniques were used to achieve a wide range of Grain Sizes from about 3 µm to 70 nm in a Cu–30% Zn alloy. Transmission electron microscopy (TEM) revealed a gradual decrease in the deformation twin thickness with decreasing Grain Size. In the present work, high-resolution TEM was used to further identify deformation twins and measure their thickness, especially for Grain Sizes below 70 nm. The twin thickness was found to gradually reduce with decreasing Grain Size, until a critical Size (20 nm), below which only stacking faults were observed. Interestingly, the relationship between twin thickness and Grain Size in the ultrafine/nanocrystalline regime is found similar to that in the coarse-Grained regime, despite the differences in their twinning mechanisms. This work provides a large set of data for setting up a model to predict the twin thickness in ultrafine-Grained and nanocrystalline face-centered cubic materials.
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Grain Size Effect on radiation tolerance of nanocrystalline mo
Scripta Materialia, 2016Co-Authors: Guangming Cheng, Y. Q. Wang, A Misra, Y T ZhuAbstract:We report a significant Grain Size Effect on radiation tolerance of nanocrystalline Mo under He ion irradiation. Irradiation-induced dislocation loops mainly contribute to the irradiation-induced hardening of Mo films with Grain Size of > 90 nm, while few such loops in those with Grain Size of < 90 nm. The hardness increment after irradiation decreases with decreasing the Grain Size, and approaches zero at the Grain Size of 25 nm. Also, the Size and the density of irradiation-induced He bubbles decrease as the Grain Size decreases. This observation provides direct evidence that nanocrystalline body-centered-cubic metals have greater radiation tolerance than their ultra-fine-Grained or coarse-Grained counterparts.
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strengthening at nanoscaled coherent twin boundary in f c c metals
Philosophical Magazine, 2014Co-Authors: Ming Dao, Y T ZhuAbstract:This paper analyses slip transfer at the boundary of nanoscaled growth twins in face-centred cubic (f.c.c.) metals for strengthening mechanism. The required stress for slip transfer, i.e. inter-twin flow stress, is obtained in a simple expression in terms of stacking fault energy and/or twin boundary (TB) energy, constriction energy and activation volume. For nanotwinned Al, Cu and Ni, inter-twin flow stress versus twin thickness remarkably shows Hall–Petch relationship. The Hall–Petch slope is rationalized for various reactions of screw and non-screw dislocations at the TB. Additionally, strengthening at the boundary of nanoscaled deformation twins in f.c.c. metals is analysed by evaluating required twinning stress. At small nanoGrain Size, the prediction of deformation twin growth stress shows inverse Grain-Size Effect on twinning, in agreement with recent experimental finding.
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deformation twinning in nanocrystalline copper at room temperature and low strain rate
Applied Physics Letters, 2004Co-Authors: X Z Liao, Y T Zhu, Yonghao Zhao, S G Srinivasan, R Z Valiev, D V GunderovAbstract:The Grain-Size Effect on deformation twinning in nanocrystalline copper is studied. It has been reported that deformation twinning in coarse-Grained copper occurs only under high strain rate and/or low-temperature conditions. Furthermore, reducing Grain Sizes has been shown to suppress deformation twinning. Here, we show that twinning becomes a major deformation mechanism in nanocrystalline copper during high-pressure torsion under a very slow strain rate and at room temperature. High-resolution transmission electron microscopy investigation of the twinning morphology suggests that many twins and stacking faults in nanocrystalline copper were formed through partial dislocation emissions from Grain boundaries. This mechanism differs from the pole mechanism operating in coarse-Grained copper.
