| 1. |
- Man, Zhang, et al.
(författare)
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Facile one-step synthesis and enhanced photocatalytic activity of WC/ferroelectric nanocomposite
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:40, s. 22861-22870
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Tidskriftsartikel (refereegranskat)abstract
- The development of noble-metal-free co-catalysts is seen as a viable strategy for improving the performance of semiconductor photocatalysts. Although the photocatalytic efficiency of ferroelectrics is typically low, it can be enhanced through the incorporation of a co-catalyst into nanocomposites. Here, we demonstrate the influence of ferroelectricity on the decolorization of rhodamine B under simulated solar light using RbBi2Ti2NbO10 and compared the performance with that of non-ferroelectric RbBi2Nb5O16. The decolorization rate for RbBi2Ti2NbO10 was 5 times greater than that of RbBi2Nb5O16. This behaviour can be explained in terms of ferroelectric polarization, which drives the separation of charge carriers. The photocatalytic activity of RbBi2Ti2NbO10 was further enhanced to over 30 times upon preparing a nanocomposite with tungsten carbide (WC) through high energy ball milling. This enhancement was attributed not only to the increased specific surface area, but also to the incorporated WC co-catalyst, which also serves as a source of plasmonic hot electrons and extends the photocatalytic activity into the visible light range. The WC/RbBi2Ti2NbO10 nanocomposite shows interesting water oxidation properties and evolves O-2 with a rate of 68.5 mu mol h(-1) g(-1) and a quantum yield of 3% at 420 nm. This work demonstrates a simple route for preparing WC containing nano-ferroelectric composites for solar energy conversion applications.
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| 2. |
- Zhang, Man, et al.
(författare)
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Terahertz Reading of Ferroelectric Domain Wall Dielectric Switching
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:10, s. 12622-12628
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric domain walls (DWs) are important nanoscale interfaces between two domains. It is widely accepted that ferroelectric domain walls work idly at terahertz (THz) frequencies, consequently discouraging efforts to engineer the domain walls to create new applications that utilize THz radiation. However, the present work clearly demonstrates the activity of domain walls at THz frequencies in a lead-free Aurivillius phase ferroelectric ceramic, Ca0.99Rb0.005Ce0.005Bi2Nb2O9, examined using THz-time-domain spectroscopy (THz-TDS). The dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity. This is evidenced by higher dielectric permittivity in the THz band after poling, reflecting decreased domain wall density. An elastic vibrational model has also been used to verify that a single frustrated dipole in a domain wall represents a weaker contribution to the permittivity than its counterpart within a domain. The work represents a fundamental breakthrough in understanding the dielectric contributions of domain walls at THz frequencies. It also demonstrates that THz probing can be used to read domain wall dielectric switching.
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| 3. |
- Ahmed, Shafique, et al.
(författare)
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Terahertz probing of low-temperature degradation in zirconia bioceramics
- 2022
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 105:2, s. 1106-1115
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Tidskriftsartikel (refereegranskat)abstract
- ZrO2-based ceramics are widely used in biomedical applications due to its color, biocompatibility, and excellent mechanical properties. However, low-temperature degradation (LTD) introduces a potential risk for long-term reliability of these materials. The development of innovative nondestructive techniques, which can explore LTD in zirconia-derived compounds, is strongly required. Yttria stabilized zirconia, 3Y-TZP, is one of the well-developed ZrO2-based ceramics with improved resistance to LTD for dental crown and implant applications. Here, 3Y-TZP ceramic powders were pressed and sintered to study the LTD phenomenon by phase transition behavior. The LTD-driven tetragonal-to-monoclinic phase transition was confirmed by XRD. XPS analysis demonstrated that induced LTD reduced the oxygen vacancies which supports these findings. It is proved that after the degradation, the 3Y-TZP ceramics show the decreased dielectric permittivity at terahertz frequencies due to the crystallographic phase transformation. Terahertz nondestructive probe is a promising method to investigate LTD in zirconia ceramics.
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| 4. |
- Eriksson, Mirva, et al.
(författare)
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Effect of grain size on ferroelectric domain and electrical properties of submicron sized sodium potassium niobate ceramics
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Annan publikation (populärvet., debatt m.m.)abstract
- Piezoelectric ceramics of the composition Na0.5K0.5NbO3 (NKN) with grain sizes in the range of 0.2 - 1 mm were fabricated by Spark Plasma Sintering using normal pressure dies and a high pressure cell designed for pressures up to 500 MPa with the purpose of investigating the effect of grain size on domain structures and electrical properties. Optimized processing conditions enabled ceramics of high densities (>99.5%TD) to be made at T≥850°C. It was found that domain size decreases with decreasing grain size and that non-180° ferroelectric domains walls were still visible in 200 nm sized grains. The room temperature dielectric constant firstly increased with decreasing grain size and then decreased in the low grain size regime. The materials with finer grain size displayed a broad ferro-paraelectric phase transition and a depression of the dielectric maximum at the Curie point. They also displayed an increase in the coercive field and approximately unchanged remnant polarization. The material sintered at 850°C represents a very good candidate for lead-free piezoelectric applications, because of its high piezoelectric constant (d33 = 160±2 pC/N).
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| 5. |
- Eriksson, Mirva, et al.
(författare)
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Ferroelectric Domain Structures and Electrical Properties of Fine-Grained Lead-Free Sodium Potassium Niobate Ceramics
- 2011
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 94:10, s. 3391-3396
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Tidskriftsartikel (refereegranskat)abstract
- Piezoelectric ceramics of the composition Na(0.5)K(0.5)NbO(3) (NKN) with grain sizes in the range of 0.2-1 mu m were fabricated by spark plasma sintering. Ferroelectric domain size decreases with decreasing grain size and non-180 degrees ferroelectric domains walls were still visible in 200 nm sized grains. The Curie point of the ceramics was grain size independent. This suggests that the critical grain size for a single domain single grain structure for NKN is <200 nm. Optimized processing conditions enabled ceramics of high densities (>99.5% theoretical density) to be made at T >= 850 degrees C. For the dense ceramics (grain size >= 350 nm), the room temperature dielectric constant and coercive field increased with decreasing grain size. The remnant polarization was grain size independent. The material sintered at 850 degrees C is a very good candidate for lead-free piezoelectric applications because of its high piezoelectric constant (d(33) = 160 +/- 2 pC/N).
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| 6. |
- Eriksson, Mirva, et al.
(författare)
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Low temperature consolidated lead-free ferroelectric niobateceramics with improved electrical properties
- 2010
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Ingår i: Journal of Materials Research. - : Elsevier. - 0884-2914 .- 2044-5326. ; 25:2, s. 240-247
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Tidskriftsartikel (refereegranskat)abstract
- There is a concerted effort to develop lead-free piezoelectric ceramics. ((Na0.5K0.5)NbO3 based ceramics have good electrical properties, and are a potential replacement material for lead zirconate titanate piezoelectric ceramics. In this work a commercial powder based on (Na0.5K0.5)NbO3 with an initial particle size of 260 nm was consolidated by plasma sintering (SPS). To avoid volatilization, high mechanical pressures were used to minimize the densification temperature. It was found that under a uniaxial pressure of 100 MPa, fully densified compacts can be prepared at 850. Ceramics densified at such a low temperature demonstrate an unusually high remanent polarization (30 mC/cm2) and high d33 (146 pC/N). The improved ferroelectric properties are ascribed to the homogeneous, dense, and submicron grained microstructure achieved.
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| 7. |
- Hu, Zimeng, et al.
(författare)
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Deciphering the peculiar hysteresis loops of 0.05Pb(Mn1/3Sb2/3)O3–0.95Pb(Zr0.52Ti0.48)O3 piezoelectric ceramics
- 2023
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- The majority of piezoelectric ceramics based on Pb(Zr, Ti)O3 (PZT) exhibit hysteretic behavior, which varies depending on various factors, including composition, microstructure and processing conditions. The ternary system 0.05Pb(Mn1/3Sb2/3)O3–0.95Pb(Zr0.52Ti0.48)O3 (5PMS-PZT) has shown attractive piezoelectric properties with superior thermal stability compared to pure Pb(Zr0.52Ti0.48)O3, but the underlying mechanisms of its complex hysteretic behavior have not been fully clarified yet. This work further delves into the hysteretic aspects of 5PMS-PZT ceramics and describes hysteresis features that have not been yet reported for any known piezoelectric system. Four current peaks in I-E loops and S-E loops with unconventional shapes, which have a significant dependence on applied field amplitude, frequency and electrical history have been observed here. This peculiar hysteretic behavior is influenced by convoluted effects of domain switching, electric field-induced structural transitions, point defects and aging/de-aging processes, whose combinations lead to unique hysteresis features.
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| 8. |
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| 9. |
- Liu, Jing, et al.
(författare)
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Dielectric, piezoelectric, and ferroelectric properties of grain-orientated Bi3.25La0.75Ti3O12 ceramics
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:10, s. 104107-
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Tidskriftsartikel (refereegranskat)abstract
- By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d(33) piezoelectric coefficient of BLT ceramics gradually reduces up to 350 degrees C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d(33) above the permittivity peak, T-m, show that the BLT ceramic has relaxor-like behavior.
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| 10. |
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| 11. |
- Shen, Zhijian, et al.
(författare)
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Ferroelectric ceramics with enhanced remnant polarization by ordered coalescence of nano-crystals
- 2012
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:44, s. 23547-23552
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Tidskriftsartikel (refereegranskat)abstract
- An exceptional high ferroelectric remnant polarization (P-r) was observed in BaTiO3 ceramics owing to the formation of micron-sized grains possessing nano-scale mosaicity. Such a structural hierarchy was developed via a novel crystal-growth mechanism, namely ordered coalescence of nano-crystals achieved by synergetic atomic epitaxial growth and self-assembly of nano-crystals. The accommodating lattice defects in sub-grain boundaries due to the imperfect assembly of nano-crystals significantly contribute to the P-r enhancement by stimulating the dynamics of ferroelectric domain formation and switching. This finding defines a new approach to nanopowder sintering leading to enhanced properties sensitive to lattice defects.
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| 12. |
- Viola, Giuseppe, et al.
(författare)
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Effect of grain size on domain structures, dielectric and thermal depoling of Nd-substituted bismuth titanate ceramics
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:18, s. 182903-
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Tidskriftsartikel (refereegranskat)abstract
- The microscopic origin of the grain size effects on the dielectric, piezoelectric, and thermal depoling properties of Aurivillius phase Bi3.15Nd0.85Ti3O12 was investigated. Using atomic force microscopy, domain walls were observed in micrometer grain size ceramics, but gradually disappeared with reducing grain size and were not found in ceramics with 90 nm grain size. In strain-electric field butterfly loops, the strain decreased with decreasing grain size indicating a decreasing contribution of non-180 degrees domain walls switching to the strain. Lattice distortion (a-b)/b decreased with decreasing grain size. The thermal depoling resistance decreased with decreasing grain size, due to increasing internal mechanical stresses.
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| 13. |
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| 14. |
- Wang, Yaqiong, et al.
(författare)
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Domain Wall Free Polar Structure Enhanced Photodegradation Activity in Nanoscale Ferroelectric BaxSr1-xTiO3
- 2020
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 10:38
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric materials exhibit anomalous behavior due to the presence of domains and domain walls which are related to the spontaneous polarization inherent in the crystal structure. Control of ferroelectric domains and domain walls has been used to enhance device performances in ultrasound, pyroelectric detectors, and photovoltaic systems with renewed interest in nanostructuring for energy applications. It is also known that ferroelectrics including domain walls can double photocatalytic rate and increase carrier lifetime from microsecond to millisecond. However, there remains a lack of understanding on the different contributions of the domain and domain walls to photocatalytic activities. Herein it is found, by comparing samples of nanostructured Ba(x)Sr(1-)(x)TiO(3)with and without a polar domain, that the material with polar domains has a faster reaction rate (k= 0.18 min(-1)) than the nonpolar one (k= 0.11 min(-1)). It is further revealed that the observed enhanced photoactivity of perovskite ferroelectric materials stems from the inherent polarization of the domain instead of domain walls. Here, the new understanding of the underlying physics of materials with a spontaneous dipole opens a door to enhance the performance of light induced energy harvesting systems.
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| 15. |
- Wu, Jiyue, et al.
(författare)
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Perovskite Sr-x(Bi1-xNa0.97-xLi0.03)(0.5)TiO3 ceramics with polar nano regions for high power energy storage
- 2018
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Ingår i: Nano Energy. - : ELSEVIER SCIENCE BV. - 2211-2855 .- 2211-3282. ; 50, s. 723-732
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)(0.5)TiO3 (x = 0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (P-r) and high maximum polarization (P-max). Moreover, P-max was further increased due to the electric field induced reversible phase transitions in nano regions. Comprehensive structural and electrical studies were performed to confirm the PNRs and reversible phase transitions. And finally a high energy density (1.70 J/cm(3)) with an excellent efficiency (87.2%) was achieved using the contribution of field-induced rotations of PNRs and PNR-related reversible transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.
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| 16. |
- Wu, Jiyue, et al.
(författare)
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Ultrahigh field-induced strain in lead-free ceramics
- 2020
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- Due to the worldwide concerns of environmental protection and sustainable development, lead-free piezoelectric materials are greatly desired for bridging the electrical energy to the mechanical energy. However, their lower energy conversion coefficient compared to the conventional lead-containing piezoelectric materials significantly limits their device applications. Herein, we introduce a novel strategy to increase the strain of lead-free ferroelectric system via material structure design to create polar nano regions (PNRs) and point defects in the material while retaining the global ferroelectric phase. This added short-range structural heterogeneity in the material will facilitate the field-induced phase transition and reversible domain wall switching to enhance the strain. Following this strategy, we demonstrate an ultrahigh strain induced by an electric field in non-textured lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics. The strain in unipolar mode (Suni) can reach up to 0.74% at 70 kV/cm, making it the highest value in reported lead-free ceramics so far. This puts forward a good route to design high-performance piezoelectric materials by material structure engineering. It also reveals the promising potential of lead-free piezoelectric materials in practical electromechanical device applications.
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| 17. |
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