| 1. |
- Buscaglia, M. T., et al.
(författare)
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Ferroelectric properties of dense nanocrystalline BaTiO3 ceramics
- 2004
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 15:9, s. 1113-1117
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Tidskriftsartikel (refereegranskat)abstract
- Dense BaTiO3 ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data show a broad ferro-para phase transition with a maximum permittivity of approximate to1100 at 390 K and 1 kHz. The local ferroelectric switching behaviour was investigated by piezoresponse force microscopy. Typical piezoelectric hysteresis loops were recorded at different positions of the sample. The present results provide experimental evidence for polarization switching at the local scale, indicating that the critical grain size for the disappearance of ferroelectric behaviour in dense, bulk BaTiO3 nanocrystalline ceramics is below 50 nm.
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| 2. |
- Buscaglia, M. T., et al.
(författare)
-
High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:6
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical models for small ferroelectric particles predict a progressive decrease of the Curie temperature, spontaneous lattice strain, and polarization until the critical size corresponding to transition to the cubic phase and disappearance of ferroelectricity is reached. In contrast, the behavior of nanocrystalline BaTiO3 ceramics with a grain size of approximate to 30 nm is dominated by extrinsic effects related to the grain boundaries which mask the expected downscaling of properties. While the noncubic crystal structure, the high dielectric constant (approximate to 1600) and the variation of permittivity with temperature suggest a ferroelectric behavior, very slim, and nearly linear polarization hysteresis loops are observed. Evidence for the existence of a ferroelectric domain structure with domains extending over several grains and of polarization switching at local scale is given by piezoresponse force microscopy. The suppression of macroscopic ferroelectric hysteresis and switching originates from a frozen domain structure stable under an external field owing to the effects exerted by the grain boundaries, such as the clamping of the domain walls and the hindrance of polarization switching. Furthermore, the depolarization field originated by the low-permittivity nonferroelectric grain boundaries can cause a significant reduction of polarization. If the grain size is small enough, the ceramic is expected to undergo a "phase transition" to a polar phase with nonswitchable polarization. The BaTiO3 ceramics with grain size of 30 nm investigated in the present study are deemed to be close to this transition.
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| 3. |
- Buscaglia, V., et al.
(författare)
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Nanostructured barium titanate ceramics
- 2004
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 148:1, s. 24-27
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Tidskriftsartikel (refereegranskat)abstract
- Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO3) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 degreesC of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing. Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.
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| 4. |
- Buscaglia, V., et al.
(författare)
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Raman and AFM piezoresponse study of dense BaTiO3 nanocrystalline ceramics
- 2005
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 25:12, s. 3059-3062
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Tidskriftsartikel (refereegranskat)abstract
- Dense nanocrystalline BaTiO3 (BT) ceramics with grain sizes (GSs) below 100 nm obtained by spark plasma sintering (SPS), were investigated by micro-Raman spectroscopy in order to obtain information about the changes in the local order induced by size effects. The obtained spectra in the range 80-700 K showed the presence of all the crystalline phases of BaTiO3, even in the finest structure (50 nm grain size ceramic), with particularities attributed to the high density of non-ferroelectric grain boundaries. The AFM piezoresponse study incontestably proved the ferroelectric switching at local scale in nanocrystalline BaTiO3 ceramics at room temperature.
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| 5. |
- Mitoseriu, L., et al.
(författare)
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Local switching properties of dense nanocrystalline BaTiO3 ceramics
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:13, s. 2418-2420
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Tidskriftsartikel (refereegranskat)abstract
- The switching properties of dense BaTiO3 ceramics with 50 nm average grain size were investigated at local scale by piezoresponse force microscopy. Large areas with low piezoelectrical activity beside islands with strong piezoresponse were found. The application of electric fields induces stable domain structures and changes in the polarization state far away from the probing area, probably via trans-granular dipole interactions. Piezoelectric hysteresis loops were recorded on various positions, even in regions with initial zero piezoresponse, which possibly showed a superparaelectric behavior. The results are incontestable proof that 50 nm BaTiO3 ceramics retain ferroelectricity at a local scale.
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| 6. |
- Zhao, Zhe, 1973-, et al.
(författare)
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Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Institute of Physics (AIP). - 1098-0121 .- 1550-235X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- A progressive reduction of tetragonal distortion, heat of transition, Curie temperature, and relative dielectric constant has been observed on dense BaTiO3 ceramics with grain size decreasing from 1200 to 50 nm. The correlations between grain size, extent of tetragonal distortion, and ferroelectric properties strongly support the existence of an intrinsic size effect. From the experimental trends the critical size for disappearance of ferroelectricity has been evaluated to be 10-30 nm. The strong depression of the relative permittivity observed for the nanocrystalline ceramics can be ascribed to the combination of the intrinsic size effect and of the size-dependent "dilution" effect of a grain boundary "dead" layer.
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