Preparation and dielectric investigations of Ba0.60Sr0.40TiO3 ferroelectric ceramics with different degree of porosity (Abstract/Poster in convegno)

Type
Label
  • Preparation and dielectric investigations of Ba0.60Sr0.40TiO3 ferroelectric ceramics with different degree of porosity (Abstract/Poster in convegno) (literal)
Anno
  • 2014-01-01T00:00:00+01:00 (literal)
Alternative label
  • R. Stanculescu 1, I. Ciuchi 1,2, I. Turcan 1, P. Galizia 2, C. Capiani 2, C. Galassi 2 and L. Mitoseriu 1 (2014)
    Preparation and dielectric investigations of Ba0.60Sr0.40TiO3 ferroelectric ceramics with different degree of porosity
    in ELECTROCERAMICS XIV, Bucarest (Romania), 16-20 giugno 2014
    (literal)
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  • R. Stanculescu 1, I. Ciuchi 1,2, I. Turcan 1, P. Galizia 2, C. Capiani 2, C. Galassi 2 and L. Mitoseriu 1 (literal)
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  • http://www.electroceramics14.com/images/PDF/Abstract%20Book%20Electroceramics%20XIV.pdf http://www.electroceramics14.com/images/PDF/Final%20Program%20EC%20XIV.pdf (literal)
Note
  • Abstract (literal)
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  • 1 Faculty of Physics, Alexandru Ioan Cuza University, Iasi, 700506, Romania 2 ISTEC-CNR, Via Granarolo, no.64, I - 48018, Faenza, Italy (literal)
Titolo
  • Preparation and dielectric investigations of Ba0.60Sr0.40TiO3 ferroelectric ceramics with different degree of porosity (literal)
Abstract
  • By introducing a controlled porosity into the ceramic systems, the properties can be improved and make the material proper for being used as high-frequency ultrasonic transducers or for tunable applications. The tailored porosity exposes special properties and characteristics of the materials, which might be completely different than their conventional dense equivalents. The aim of this study was to characterize (Ba,Sr)TiO3 ceramics with different porosity levels. Powders with the composition Ba0.60Sr0.40TiO3 (BST) were prepared following the mixed oxide method by solid-state reaction at a sintering temperature of 1450°C for 2h. The BST ceramics with various porosities have been prepared by addition of lamellar graphite in concentration of 10, 20 and 35%. The effect of addition of graphite on dielectric properties was investigated. We noticed that the increasing of the amount of graphite increases the graded porosity and leads to a low mechanical quality factor. The relative density of the obtained samples varies from values around 95% for the dense ceramic to 66% for porous ceramics. Graphite was burned out through the sintering process and this resulted in a modification of morphology, microstructure and pore density of the ceramic product. The porous samples produced with homogeneous or graded porosity show a strong difference of the dielectric properties and microstructure in comparison with the dense ceramic samples. The role of anisotropic porosity on the functional properties on the dielectric properties is discussed. Microstructural, morphological and dielectric investigations have been performed and data were compared with other literature studies. From SEM analysis it was found that with addition of graphite as pore forming the samples present a fracture mode transformation from intragranular fracture to an intergranular fracture and a decreasing of grain size of BST. Furthermore, as BST grain size becomes smaller, the volume of grain boundary increases and the crack prefers spreading along grain boundary to splitting the strengthened grain. The Impedance Spectroscopy analyse was performed in the temperature range of (21-200)°C and frequency of 20Hz-2MHz. The dielectric investigations have shown that the dielectric constant of the Ba0.60Sr0.40TiO3 (BST) ceramics with different degree of porosity, decrease and remains constant at higher frequency, indicating dielectric dispersion. The frequency dependence of the real and imaginary part of permittivity present a few characteristic relaxations which appear in the specific frequency ranges: (i) the increasing of the real and imaginary parts of permittivity at low frequencies below 100Hz for the compositions with x=10, 20 and 35% graphite is most probably associated to the thermally activated space charge effects (Maxwell-Wagner phenomena) and (ii) anomalies of the imaginary part of permittivity above 103Hz, for samples with x=10 and 20% porosity, which seems to be related to a Debye-type relaxation process. The dielectric properties of the investigated ceramics were characterized and correlated with their microstructure. From dielectric constant dependence with temperature, a shift of Curie temperature of ceramics was observed and possible reasons for these effects were interpreted. Acknowledgements: This work was financially supported by CNCS-UEFISCDI projects PNII-ID-PCE-2011-3- 0745 and by ERASMUS placement programme between Univ. \"Al. I. Cuza\" Iasi & ISTEC-CNR Faenza, Italy. The collaboration in frame of the COST Action MP0904 is highly acknowledged. (literal)
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