C. Ciomaga - Academia.edu (original) (raw)
Papers by C. Ciomaga
Phase Transitions, 2006
BaZr0.1Ti0.9O3 ceramics with grain sizes of 0.75 and 2.60 µm have been prepared via solid-state r... more BaZr0.1Ti0.9O3 ceramics with grain sizes of 0.75 and 2.60 µm have been prepared via solid-state reaction. Optimum parameters for calcination and sintering have been found in order to obtain pure perovskite phase, high density ceramics and homogeneous microstructures. The dielectric data show a diffuse phase transition with a mixed ferroelectric-relaxor character at a maximum at 87–92°C, with a small thermal hysteresis
Journal of Alloys and Compounds
Materials
The present paper reports the dependence of dielectric, ferroelectric and piezoelectric propertie... more The present paper reports the dependence of dielectric, ferroelectric and piezoelectric properties on the porosity level in BaZr0.15Ti0.85O3 ceramics with porosity from 5% to 21%. Microporosity with 0–3 connectivity has been produced using PMMA microspheres as a sacrificial template. The functional properties (dielectric, ferroelectric and piezoelectric effect) are mostly affected by the “dilution effect”: permittivity decreases by 40% when porosity increases by 21%, and Pmax decreases from 13 to 5 µC/cm2 while the Prem is in the range of (2–8) µC/cm2. However, the reduction of the zero-field permittivity and hysteretic behaviour of ε(E) while the tunability level is still high makes from porous ceramics interesting materials for tunability application.
Journal of Alloys and Compounds
Journal of the European Ceramic Society
Journal of Applied Physics
J. Mater. Chem. C
SrTiO3–BaTiO3 nanocomposite fabricated by high-pressure field-assisted sintering exhibits tempera... more SrTiO3–BaTiO3 nanocomposite fabricated by high-pressure field-assisted sintering exhibits temperature-stable dielectric permittivity, low losses and acceptable tunability.
Ceramics International, 2017
Journal of the European Ceramic Society, 2017
Materials Chemistry and Physics, 2016
Journal of Optoelectronics and Advanced Materials, 2004
Measurement Science and Technology, 2015
ABSTRACT An impedance spectroscopy method, using an Agilent E4991A RF Impedance/Material Analyzer... more ABSTRACT An impedance spectroscopy method, using an Agilent E4991A RF Impedance/Material Analyzer, was employed for the investigation of radiofrequency and microwave dielectric characteristics for some ceramic materials with high dielectric permittivity. Experimental observations recorded single, double and even triple resonances in the permittivity spectra, while for the selected samples significantly different values of permittivity from the ones found in existing literature were directly measured and observed in the frequency range of 100 MHz–1 GHz. The specified material analyzer is designed to work within certain permittivity-frequency domains; working outside these limits leads to significant errors when carrying out direct measurements of permittivity. Having observed that the resonance measurements are not associated with the intrinsic material properties but with the sample resonances, we proposed a dielectric resonance cavity model for sample purposes and we determined the dielectric permittivity at different resonance frequencies. A scaling procedure, based on the computed values of permittivity, was applied in order to correct the directly measured permittivity spectra where the frequency was outside the resonance domains. The corrected data are in good agreement with those measured using other techniques and suggest that the proposed procedure extends the spectroscopy method currently used for high permittivity measurements. The sources of error for the proposed method were investigated.
The frequency-dependence of the complex permittivity of some Ba(Zr,Ti)O3 ferroelectric ceramics w... more The frequency-dependence of the complex permittivity of some Ba(Zr,Ti)O3 ferroelectric ceramics was investigated, with the aim to evidence different behaviors related to microstructural characteristics. Ferroelectric BaZr0.10Ti0.90O3 sintered at two temperatures gave different types of impedance spectra due to their differences in the microstructures. The multiple components in the complex impedance diagram result from the grain boundary phenomena, i.e. from local differences in the conductivity and dielectric properties of the ceramic grain bulk and ceramic grain boundary.
The electric field dependence of the dielectric constant in ferroelectrics is described theoretic... more The electric field dependence of the dielectric constant in ferroelectrics is described theoretically by means of the Landau-Grinzburg-Devonshire (LGD) theory and by two approximations valid for low polarizations (Johnson's equation and evenpower relation). While at low fields, all the approximations are describing well the tunability data, at high fields the LGD and Johnson's equations are only providing realistic approaches for the experimental data. Tunability data in a large range of fields obtained for the BaTi0.9Zr0.1O3 ceramic at room temperature were well fitted by using the Johnson's approximation in the overall range of field amplitudes. This was explained by the low values of the polarization caused by the mixed ferroelectric-relaxor character and by the proximity of the Curie range at room temperature.
Processing and Application of Ceramics, 2009
First Ba(Zr,Ti)O3 (BZT) ceramics with various compositions prepared by solid state, with high den... more First Ba(Zr,Ti)O3 (BZT) ceramics with various compositions prepared by solid state, with high density, homogeneous microstructures and grain sizes in the range (0.7-4) ?m were studied. Besides the dielectric and ferroelectric investigations, First Order Reversal Curves method was employed to describe the changes of the switching properties induced by composition and grain size, related to the ferroelectric-relaxor crossover. The dielectric and ferroelectric data for ceramics with similar grain sizes demonstrated the expected ferroelectricrelaxor crossover induced by increasing x. For a given composition (x = 0.10), the relaxor character increases whit reduction of the grain size. The FORC distribution shows almost zero reversible contribution and well separated sharp irreversible component for larger grains, while more diffuse distribution with a continuous extension from Ec=0 (reversible) to Ec?0 (irreversible, switching) is typical for finer grains. .
Processing and Application of Ceramics, 2010
The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switc... more The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switching properties of ferroelectrics. In the present paper, the FORC method was applied for hard Pb(Zr,Ti)O3 ceramics with symmetric and asymmetric clamping. An ideal high-oriented single-crystalline ferroelectric with rectangular P(E) loop would be characterised by a delta-function FORC distribution, while real ferroelectrics and mostly the polycrystalline ceramics show dispersed FORC distributions. All the investigated ceramics show FORC distributions with non-Gaussian shape, slightly elongated along the coercitive axis, meaning a high dispersion of the energy barriers separating the two bi-stable polarizations ?P. The degree of dispersion is enhanced by clamping. The maximum FORC coercivity is located at ~ (1.9-2) MV/m for all the hard ceramics. The FORC cycling experiment causes the reversal of the initial poling and result in a positive/negative bias on the FORC diagrams. According to ...
Journal of Applied Physics, 2014
ABSTRACT The addition of small amounts (below 0.1 wt. %) of multi-walled carbon nanotubes (MWCNTs... more ABSTRACT The addition of small amounts (below 0.1 wt. %) of multi-walled carbon nanotubes (MWCNTs) to Pb(Zr0.47Ti0.53)O3 (PZT) ceramics prepared by spark plasma sintering is proposed as a method of tailoring the electrical properties, which are expected to be modified with respect to the pure PZT, both as result of the presence of 1-D conductive fillers in the ceramic product and via the microstructural modifications of ceramics induced during the sintering. The addition of even small amounts of carbon nanotubes strongly reduced the sinterability of PZT ceramics and resulted in the porous and fine-grained microstructures (relative density of 73% for a MWCNT addition of 0.5 vol. % by comparison with 91% in the pure PZT, produced in the same conditions). A monotonous decrease of permittivity with increasing the MWCNT level from �830 in pure PZT to �627 for x¼0.5 vol. %, at a fixed frequency f¼1kHz, and low dielectric losses below 2% have been observed. Tunability increases with respect to the values of dense PZT for small concentration of MWCNT as high as 0.0625 vol. % and then monotonically decreases for higher additions. Calculations by finite element modeling demonstrated that by addition of 1-D conductive fillers with compositions below the percolation limits to porous microstructures, the major role in changing the electrical properties via local field modification is related to the induced porosity rather than to the influence of the small amounts of MWCNTs survived after sintering and post-annealing treatment. The reduced permittivity with about 14% combined with low losses and higher tunability than in the pure PZT ceramics obtained at reasonable fields, makes the idea of using the addition of MWCNTs to ferroelectric ceramics an interesting approach in searching new structures for tunability properties. VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4900527]
Scripta Materialia, 2010
ABSTRACT The magnetoelectric ceramic composite formed by Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 (PZT... more ABSTRACT The magnetoelectric ceramic composite formed by Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 (PZTN) and CoFe2O4 (CF) was prepared in situ by citrate–nitrate combustion on the PZTN powder template. The electromagnetic properties showing double negative resonance with negative values of dielectric permittivity εr and magnetic permeability μr, in a close frequency range of 2 × 108 Hz to 2.6 × 109 Hz, are reported. In addition, the condition of impedance matching with free space εr=μrεr=μr is accomplished at the frequency f = 280 MHz in these ceramic composites.
Phase Transitions, 2006
BaZr0.1Ti0.9O3 ceramics with grain sizes of 0.75 and 2.60 µm have been prepared via solid-state r... more BaZr0.1Ti0.9O3 ceramics with grain sizes of 0.75 and 2.60 µm have been prepared via solid-state reaction. Optimum parameters for calcination and sintering have been found in order to obtain pure perovskite phase, high density ceramics and homogeneous microstructures. The dielectric data show a diffuse phase transition with a mixed ferroelectric-relaxor character at a maximum at 87–92°C, with a small thermal hysteresis
Journal of Alloys and Compounds
Materials
The present paper reports the dependence of dielectric, ferroelectric and piezoelectric propertie... more The present paper reports the dependence of dielectric, ferroelectric and piezoelectric properties on the porosity level in BaZr0.15Ti0.85O3 ceramics with porosity from 5% to 21%. Microporosity with 0–3 connectivity has been produced using PMMA microspheres as a sacrificial template. The functional properties (dielectric, ferroelectric and piezoelectric effect) are mostly affected by the “dilution effect”: permittivity decreases by 40% when porosity increases by 21%, and Pmax decreases from 13 to 5 µC/cm2 while the Prem is in the range of (2–8) µC/cm2. However, the reduction of the zero-field permittivity and hysteretic behaviour of ε(E) while the tunability level is still high makes from porous ceramics interesting materials for tunability application.
Journal of Alloys and Compounds
Journal of the European Ceramic Society
Journal of Applied Physics
J. Mater. Chem. C
SrTiO3–BaTiO3 nanocomposite fabricated by high-pressure field-assisted sintering exhibits tempera... more SrTiO3–BaTiO3 nanocomposite fabricated by high-pressure field-assisted sintering exhibits temperature-stable dielectric permittivity, low losses and acceptable tunability.
Ceramics International, 2017
Journal of the European Ceramic Society, 2017
Materials Chemistry and Physics, 2016
Journal of Optoelectronics and Advanced Materials, 2004
Measurement Science and Technology, 2015
ABSTRACT An impedance spectroscopy method, using an Agilent E4991A RF Impedance/Material Analyzer... more ABSTRACT An impedance spectroscopy method, using an Agilent E4991A RF Impedance/Material Analyzer, was employed for the investigation of radiofrequency and microwave dielectric characteristics for some ceramic materials with high dielectric permittivity. Experimental observations recorded single, double and even triple resonances in the permittivity spectra, while for the selected samples significantly different values of permittivity from the ones found in existing literature were directly measured and observed in the frequency range of 100 MHz–1 GHz. The specified material analyzer is designed to work within certain permittivity-frequency domains; working outside these limits leads to significant errors when carrying out direct measurements of permittivity. Having observed that the resonance measurements are not associated with the intrinsic material properties but with the sample resonances, we proposed a dielectric resonance cavity model for sample purposes and we determined the dielectric permittivity at different resonance frequencies. A scaling procedure, based on the computed values of permittivity, was applied in order to correct the directly measured permittivity spectra where the frequency was outside the resonance domains. The corrected data are in good agreement with those measured using other techniques and suggest that the proposed procedure extends the spectroscopy method currently used for high permittivity measurements. The sources of error for the proposed method were investigated.
The frequency-dependence of the complex permittivity of some Ba(Zr,Ti)O3 ferroelectric ceramics w... more The frequency-dependence of the complex permittivity of some Ba(Zr,Ti)O3 ferroelectric ceramics was investigated, with the aim to evidence different behaviors related to microstructural characteristics. Ferroelectric BaZr0.10Ti0.90O3 sintered at two temperatures gave different types of impedance spectra due to their differences in the microstructures. The multiple components in the complex impedance diagram result from the grain boundary phenomena, i.e. from local differences in the conductivity and dielectric properties of the ceramic grain bulk and ceramic grain boundary.
The electric field dependence of the dielectric constant in ferroelectrics is described theoretic... more The electric field dependence of the dielectric constant in ferroelectrics is described theoretically by means of the Landau-Grinzburg-Devonshire (LGD) theory and by two approximations valid for low polarizations (Johnson's equation and evenpower relation). While at low fields, all the approximations are describing well the tunability data, at high fields the LGD and Johnson's equations are only providing realistic approaches for the experimental data. Tunability data in a large range of fields obtained for the BaTi0.9Zr0.1O3 ceramic at room temperature were well fitted by using the Johnson's approximation in the overall range of field amplitudes. This was explained by the low values of the polarization caused by the mixed ferroelectric-relaxor character and by the proximity of the Curie range at room temperature.
Processing and Application of Ceramics, 2009
First Ba(Zr,Ti)O3 (BZT) ceramics with various compositions prepared by solid state, with high den... more First Ba(Zr,Ti)O3 (BZT) ceramics with various compositions prepared by solid state, with high density, homogeneous microstructures and grain sizes in the range (0.7-4) ?m were studied. Besides the dielectric and ferroelectric investigations, First Order Reversal Curves method was employed to describe the changes of the switching properties induced by composition and grain size, related to the ferroelectric-relaxor crossover. The dielectric and ferroelectric data for ceramics with similar grain sizes demonstrated the expected ferroelectricrelaxor crossover induced by increasing x. For a given composition (x = 0.10), the relaxor character increases whit reduction of the grain size. The FORC distribution shows almost zero reversible contribution and well separated sharp irreversible component for larger grains, while more diffuse distribution with a continuous extension from Ec=0 (reversible) to Ec?0 (irreversible, switching) is typical for finer grains. .
Processing and Application of Ceramics, 2010
The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switc... more The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switching properties of ferroelectrics. In the present paper, the FORC method was applied for hard Pb(Zr,Ti)O3 ceramics with symmetric and asymmetric clamping. An ideal high-oriented single-crystalline ferroelectric with rectangular P(E) loop would be characterised by a delta-function FORC distribution, while real ferroelectrics and mostly the polycrystalline ceramics show dispersed FORC distributions. All the investigated ceramics show FORC distributions with non-Gaussian shape, slightly elongated along the coercitive axis, meaning a high dispersion of the energy barriers separating the two bi-stable polarizations ?P. The degree of dispersion is enhanced by clamping. The maximum FORC coercivity is located at ~ (1.9-2) MV/m for all the hard ceramics. The FORC cycling experiment causes the reversal of the initial poling and result in a positive/negative bias on the FORC diagrams. According to ...
Journal of Applied Physics, 2014
ABSTRACT The addition of small amounts (below 0.1 wt. %) of multi-walled carbon nanotubes (MWCNTs... more ABSTRACT The addition of small amounts (below 0.1 wt. %) of multi-walled carbon nanotubes (MWCNTs) to Pb(Zr0.47Ti0.53)O3 (PZT) ceramics prepared by spark plasma sintering is proposed as a method of tailoring the electrical properties, which are expected to be modified with respect to the pure PZT, both as result of the presence of 1-D conductive fillers in the ceramic product and via the microstructural modifications of ceramics induced during the sintering. The addition of even small amounts of carbon nanotubes strongly reduced the sinterability of PZT ceramics and resulted in the porous and fine-grained microstructures (relative density of 73% for a MWCNT addition of 0.5 vol. % by comparison with 91% in the pure PZT, produced in the same conditions). A monotonous decrease of permittivity with increasing the MWCNT level from �830 in pure PZT to �627 for x¼0.5 vol. %, at a fixed frequency f¼1kHz, and low dielectric losses below 2% have been observed. Tunability increases with respect to the values of dense PZT for small concentration of MWCNT as high as 0.0625 vol. % and then monotonically decreases for higher additions. Calculations by finite element modeling demonstrated that by addition of 1-D conductive fillers with compositions below the percolation limits to porous microstructures, the major role in changing the electrical properties via local field modification is related to the induced porosity rather than to the influence of the small amounts of MWCNTs survived after sintering and post-annealing treatment. The reduced permittivity with about 14% combined with low losses and higher tunability than in the pure PZT ceramics obtained at reasonable fields, makes the idea of using the addition of MWCNTs to ferroelectric ceramics an interesting approach in searching new structures for tunability properties. VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4900527]
Scripta Materialia, 2010
ABSTRACT The magnetoelectric ceramic composite formed by Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 (PZT... more ABSTRACT The magnetoelectric ceramic composite formed by Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 (PZTN) and CoFe2O4 (CF) was prepared in situ by citrate–nitrate combustion on the PZTN powder template. The electromagnetic properties showing double negative resonance with negative values of dielectric permittivity εr and magnetic permeability μr, in a close frequency range of 2 × 108 Hz to 2.6 × 109 Hz, are reported. In addition, the condition of impedance matching with free space εr=μrεr=μr is accomplished at the frequency f = 280 MHz in these ceramic composites.