| 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, 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Zhao, Zhe, 1973-, et al.
(författare)
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Spark plasma sintering of nano-crystalline ceramics
- 2004
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Ingår i: EURO CERAMICS VIII, PTS 1-3. - : Trans Tech Publications Inc.. ; , s. 2297-2300
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Konferensbidrag (refereegranskat)abstract
- Spark Plasma Sintering (SPS) has been successfully applied in the sintering of nanocrystalline BaTiO3 and gamma-Al2O3 in order to reach fully dense nanostructured ceramics at moderate pressure and temperature. BaTiO3 compacts with densities exceeding 97% and gain size of 50 nm have thus been prepared at temperatures not exceeding 850degreesC using a uniaxial pressure of 100MPa. The selection of sintering temperature is critical for the purpose of minimizing grain growth and there is a demarcation temperature (820degreesC) between normal and abnormal grain growth for the nanocrystalline BaTiO3 powder used in this study. Fully dense alpha-Al2O3 compacts containing grains of the size 300nm or less were consolidated from high-purity gamma-Al2O3 powders without the use of additives or seeds. The transition temperature of gamma-Al2O3 to alpha-Al2O3 can be lowered to 960degreesC when gamma-Al2O3 powder is compacted in the SPS apparatus. The possible mechanisms related to this low transition temperature and to the sintering of both BaTiO3 and gamma-Al2O3 are discussed with special reference to the effect of the pulsed electric field generated by the pulsed electrical current used to heat the sample.
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| 6. |
- Zhou, L. J., et al.
(författare)
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Preparation and properties of lead zirconate stannate titanate sintered by spark plasma sintering
- 2004
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Ingår i: Journal of The American Ceramic Society. - : American Ceramic Society. - 0002-7820 .- 1551-2916. ; 87:4, s. 606-611
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Tidskriftsartikel (refereegranskat)abstract
- Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full density by spark plasma sintering (SPS). SPS samples densified at 900degrees or 950degreesC exhibit nearly full density and fine grain size (about 300 nm). Compared with samples from conventional sintering (CS), SPS samples show larger permittivity accompanied by a deterioration in dielectric loss and special strain hysteresis loops similar to those of ferroelectric relaxors, with a diffuse AFE-FE phase transition and less field-induced longitudinal strain. The differences in the properties of SPS and CS materials are attributed to the variations of the resultant microstructures, especially the grain size, of the ceramics.
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