@conference {Neagu_E._R.:2011, title = {Discrimination between Space Charge and Dipolar Contributions in Ferroelectric Polymers}, series = {International Symposium on Electrets}, year = {2011}, note = {n/a}, month = {Jan}, pages = {145-146}, type = {Peer reviewed}, abstract = {n/a}, author = {Neagu E. R. and Dias, C. and Lan{\c c}a M. Carmo and Igreja R. and Inacio P. and Marat-Mendes J. N.} } @conference {6338, title = {Discrimination between Space Charge and Dipolar Contributions in Ferroelectric Polymers}, booktitle = {14th International Symposium on Electrets}, series = {International Symposium on Electrets}, year = {2011}, note = {n/a}, type = {Peer reviewed}, abstract = {

The final thermally stimulated discharge current method allows a better selection of the experimental conditions for sample polarization. By decreasing the ratio between the charging time and the discharging time, the apparent peak is of the same order of magnitude as the genuine peaks and there is only a partial overlap between then. Two peaks have been identified for polyamide 11, one associated with the glass transition around 60 \°C and the second associated with the Curie transition around 96 \°C.

}, isbn = {978-1-4577-1025-4}, doi = {10.1109/ISE.2011.6085024}, author = {Neagu E. R. and Dias, C. and Lan{\c c}a M. Carmo and Igreja R. and Inacio P. and Marat-Mendes J. N.} } @book {7845, title = {Discrimination between Space Charge and Dipolar Contributions in Ferroelectric Polymers}, year = {2011}, note = {

Neagu, E. R. Dias, C. J. Lanca, M. C. Igreja, R. Inacio, P. Marat-Mendes, J. N. ISE 14th International Symposium on Electrets (ISE) AUG 28-31, 2011 Montpellier, FRANCE

}, pages = {145-146}, type = {Book}, abstract = {

The final thermally stimulated discharge current method allows a better selection of the experimental conditions for sample polarization. By decreasing the ratio between the charging time and the discharging time, the apparent peak is of the same order of magnitude as the genuine peaks and there is only a partial overlap between then. Two peaks have been identified for polyamide 11, one associated with the glass transition around 60 degrees C and the second associated with the Curie transition around 96 degrees C.

}, isbn = {978-1-4577-1025-4}, url = {://WOS:000298852900073}, author = {Neagu, E. R. and Dias, C. J. and Lanca, M. C. and Igreja, R. and Inacio, P. and Marat-Mendes, J. N. and Ieee} } @article {E._R._Neagu:2010, title = {The determination of the pull-in voltage from the condition of bridge stability}, volume = {5}, year = {2010}, note = {n/a}, month = {Jan}, pages = {139-151}, type = {Peer reviewed}, abstract = {n/a}, author = {Neagu, E. R. and Neagu, R. M. and Dias, C. J. and M. Carmo Lan{\c c}a and Marat-Mendes, J. N.} } @conference {M._Carmo_Lan{\c c}a:2010, title = {Dielectric spectra of natural cork and derivatives}, series = {International Conference on Dielectric Spectroscopy and Its Applications}, volume = {356}, year = {2010}, note = {n/a}, month = {Jan}, pages = {763-767}, type = {Peer reviewed}, abstract = {n/a}, author = {M. Carmo Lan{\c c}a and Neagu, E. R. and Dias, C. and Marat-Mendes, J.} } @article {7815, title = {Dielectric spectra of natural cork and derivatives}, journal = {Journal of Non-Crystalline Solids}, volume = {356}, number = {11-17}, year = {2010}, note = {

Lanca, M. C. Brandt, M. Neagu, E. R. Dias, C. J. Marat-Mendes, J. N. 5th International Conference on Dielectric Spectroscopy and Its Applications AUG 26-29, 2008 Lyon, FRANCE

}, pages = {763-767}, type = {Journal Article}, abstract = {

Cork is a cellular biomaterial that has unique characteristics that make it suitable for many types of applications. Since it is also an electrical insulator, the study of its electrical and dielectric properties can lead to new interesting applications. The moisture present in cork and derivatives has a very important role on the dielectric properties. In this work a composite made of both recycled cork and TetraPak (R) used containers was studied and compared with other cork products. The dielectric relaxation spectra of natural cork (as received), commercial cork agglomerate and of a composite cork/Tetrapak (R) was investigated in the temperature range of -50 to 120 degrees C and in the frequency range of 10(-1) Hz-2 MHz. For some samples of the composite a small amount of paraffin was added. The highest values for the imaginary part of the dielectric permittivity were found for the commercial material and the composite without paraffin. The lowest was found for the cork/TetraPak (R)/paraffin composite. The influence of humidity content was investigated for the composite with wax. Natural cork shows a peak around 80 degrees C (not seen in the derivative materials). The commercial agglomerate and the cork/TetraPak (R)/paraffin composite show a peak around 40-50 degrees C. In the composite this peak becomes smaller as humidity is removed. (C) 2009 Elsevier B.V. All rights reserved.

}, issn = {0022-3093}, doi = {10.1016/j.jnoncrysol.2009.09.042}, url = {://000276665500049}, author = {Lanca, M. C. and Brandt, M. and Neagu, E. R. and Dias, C. J. and Marat-Mendes, J. N.} } @article {Neagu_ER:2008, title = {The determination of the metal-dielectric interface barrier height from the open-circuit isothermal charging current}, journal = {Journal of Applied Physics}, volume = {104}, year = {2008}, note = {n/a}, month = {Jan}, abstract = {n/a}, url = {://000258493900111}, author = {Neagu ER and Neagu RM and Dias CJ and Lanca MC and Marat-Mendes JN} } @article {7849, title = {The determination of the metal-dielectric interface barrier height from the open-circuit isothermal charging current}, journal = {Journal of Applied Physics}, volume = {104}, number = {3}, year = {2008}, note = {

Neagu, E. R. Neagu, R. M. Dias, C. J. Lanca, M. Carmo Marat-Mendes, J. N.

}, type = {Journal Article}, abstract = {

There is a sustained interest both from theoretical and from practical points of view to understand the isothermal charging and the isothermal discharging currents in dielectrics. The measured currents are analyzed either in terms of polarization mechanisms or in terms of charge injection/extraction at the metal-dielectric interface and the conduction current through the dielectric material. As long as we do not know the nature of the origin of the current, it is not clear what information we can get by analyzing the experimental data. We propose to measure the open-circuit isothermal charging and discharging currents just to overpass the difficulties related to the analysis of the conduction mechanisms in dielectric materials. We demonstrate that besides a polarization current, there is a current related with charge injection or extraction at the metal-dielectric contact and a reverse current related to the charge trapped into the superficial trap states of the dielectric and that can jump at the interface in a reverse way. An analytical expression for the current is proposed. By fitting the experimental data to this analytical equation, two important parameters can be determined: (i) the highest value of the relaxation time for the polarization mechanisms still involved into the transient current and (ii) the height of the potential barrier W-0 at the metal-dielectric interface at the initial time when the step voltage is applied. The value obtained for Al-polyethylene terephthalate interface is (0.43 +/- 0.02) eV. For a charging voltage of 220 V there are 6x10(14) trapped electrons/m(2). (c) 2008 American Institute of Physics.

}, issn = {0021-8979}, doi = {034102 10.1063/1.2952015}, url = {://000258493900111}, author = {Neagu, E. R. and Neagu, R. M. and Dias, C. J. and Lanca, M. C. and Marat-Mendes, J. N.} } @article {7851, title = {The determination of the metal-dielectric interface barrier height from the open-circuit isothermal charging current}, journal = {Journal of Applied Physics}, volume = {104}, number = {3}, year = {2008}, note = {n/a}, type = {Journal Article}, abstract = {n/a}, issn = {0021-8979}, doi = {10.1063/1.2952015}, author = {Neagu, E. R. and Neagu, R. M. and Dias, C. J. and Lanca, M. Carmo and Marat-Mendes, J. N.} } @conference {Lanca_MC:2004, title = {Dielectric breakdown statistics of polyethylene for progressively-censored data}, booktitle = {Advanced Materials Forum Ii}, series = {Materials Science Forum}, volume = {455-456}, number = {455-456}, year = {2004}, note = {n/a}, month = {Jan}, pages = {602-605}, abstract = {n/a}, author = {Lanca MC and Marat-MendeS J} } @inbook {4190, title = {Dielectric breakdown statistics of polyethylene for progressively-censored data}, booktitle = {Advanced Materials Forum Ii}, series = {Materials Science Forum}, volume = {455-456}, year = {2004}, note = {

2nd International Materials Symposium APR 14-16, 2003 Caparica, PORTUGAL

}, pages = {602-605}, type = {Book Section}, abstract = {

The dielectric breakdown of thin films of low-density polyethylene (LDPE) electrically aged in an aqueous solution of NaCl under an AC electric field was investigated. A two-parameter Weibull function was used for the dielectric breakdown time to failure. The probability of failure for a sample was obtained by the White method for progressively censored data. Samples aged at different temperatures were compared. The results show that initially the samples aged at lower temperature (approximate to25degreesC) are more prone to fail, while those aged at higher temperature (50degreesC) fail at longer times. This was attributed to a competition between oxidation and diffusion.

}, isbn = {0255-5476 0-87849-941-5}, url = {://000222018500129}, author = {Lanca, M. C. and Marat-Mendes, J.}, editor = {Martins, R. and Fortunato, E. and Ferreira, I. and Dias, C.} } @inbook {7823, title = {Dielectric breakdown statistics of polyethylene for progressively-censored data}, booktitle = {Advanced Materials Forum Ii}, series = {Materials Science Forum}, volume = {455-456}, year = {2004}, note = {

2nd International Materials Symposium APR 14-16, 2003 Caparica, PORTUGAL

}, pages = {602-605}, type = {Book Section}, abstract = {

The dielectric breakdown of thin films of low-density polyethylene (LDPE) electrically aged in an aqueous solution of NaCl under an AC electric field was investigated. A two-parameter Weibull function was used for the dielectric breakdown time to failure. The probability of failure for a sample was obtained by the White method for progressively censored data. Samples aged at different temperatures were compared. The results show that initially the samples aged at lower temperature (approximate to25degreesC) are more prone to fail, while those aged at higher temperature (50degreesC) fail at longer times. This was attributed to a competition between oxidation and diffusion.

}, isbn = {0255-5476 0-87849-941-5}, url = {://000222018500129}, author = {Lanca, M. C. and Marat-Mendes, J.}, editor = {Martins, R. and Fortunato, E. and Ferreira, I. and Dias, C.} } @conference {Lanca_MC:2002, title = {Dielectric properties of electrically aged low density polyethylene}, booktitle = {Advanced Materials Forum I}, series = {Key Engineering Materials}, volume = {230-2}, number = {230-232}, year = {2002}, note = {n/a}, month = {Jan}, pages = {396-399}, abstract = {n/a}, author = {Lanca MC and Dias CJ and Das Gupta DK and Marat-MendeS J} } @inbook {4186, title = {Dielectric properties of electrically aged low density polyethylene}, booktitle = {Advanced Materials Forum I}, series = {Key Engineering Materials}, volume = {230-2}, year = {2002}, note = {

1st International Materials Symposium (Materials 2001) APR 09-11, 2001 COIMBRA, PORTUGAL

}, pages = {396-399}, type = {Book Section}, abstract = {

Low density polyethylene (LDPE) films kept in a sodium chloride aqueous solution, were aged under a high AC electrical field. The films were prepared from press moulding of LDPE pellets with small amounts of antioxidants. The dielectric spectra at 30 degreesC in the range of 10(-5) Hz to 105 Hz were obtained prior and after ageing. Three different experimental techniques were used to obtain the full spectrum. For the low frequency (LF) region (10(-5) Hz to 10(-1) Hz) the time domain technique was used (charge and discharge currents were also measured). The measuring device used for the 10(-1) Hz to 10(1) Hz medium frequency (MF) region was a lock-in amplifier. While for the high frequency (HF), 10(-1) Hz to 10(5) Hz, RLC bridge measurements were performed. Differences can be seen between aged and unaged PE. The region showing less changes with ageing is the MF region where the peak of the unaged samples seems to become less defined with ageing time. This peak is probably due to additives and impurities (such as antioxidants) that will tend to slowly diffuse out with time. The LF peak is a broad peak related to localised space charge injection driven by the electric field. This peak increases in an earlier stage of ageing decreasing afterwards possibly when the polymer becomes more conductive. Finally the HF shows the beginning of a peak due to gamma and beta transitions. The later is related to dipolar rotation of carbonyl groups in amorphous polymer regions, while the former is associated to crankshaft motions in the main polymer chain. This peak decreases with ageing disappearing for the most aged samples. This could also be explained if the sample becomes more conductive.

}, isbn = {1013-9826 0-87849-905-9}, url = {://000179553200091}, author = {Lanca, M. C. and Dias, C. J. and Dasgupta, D. K. and Marat-Mendes, J.}, editor = {Vieira, T.} } @inbook {7817, title = {Dielectric properties of electrically aged low density polyethylene}, booktitle = {Advanced Materials Forum I}, series = {Key Engineering Materials}, volume = {230-2}, year = {2002}, note = {

1st International Materials Symposium (Materials 2001) APR 09-11, 2001 COIMBRA, PORTUGAL

}, pages = {396-399}, type = {Book Section}, abstract = {

Low density polyethylene (LDPE) films kept in a sodium chloride aqueous solution, were aged under a high AC electrical field. The films were prepared from press moulding of LDPE pellets with small amounts of antioxidants. The dielectric spectra at 30 degreesC in the range of 10(-5) Hz to 105 Hz were obtained prior and after ageing. Three different experimental techniques were used to obtain the full spectrum. For the low frequency (LF) region (10(-5) Hz to 10(-1) Hz) the time domain technique was used (charge and discharge currents were also measured). The measuring device used for the 10(-1) Hz to 10(1) Hz medium frequency (MF) region was a lock-in amplifier. While for the high frequency (HF), 10(-1) Hz to 10(5) Hz, RLC bridge measurements were performed. Differences can be seen between aged and unaged PE. The region showing less changes with ageing is the MF region where the peak of the unaged samples seems to become less defined with ageing time. This peak is probably due to additives and impurities (such as antioxidants) that will tend to slowly diffuse out with time. The LF peak is a broad peak related to localised space charge injection driven by the electric field. This peak increases in an earlier stage of ageing decreasing afterwards possibly when the polymer becomes more conductive. Finally the HF shows the beginning of a peak due to gamma and beta transitions. The later is related to dipolar rotation of carbonyl groups in amorphous polymer regions, while the former is associated to crankshaft motions in the main polymer chain. This peak decreases with ageing disappearing for the most aged samples. This could also be explained if the sample becomes more conductive.

}, isbn = {1013-9826 0-87849-905-9}, url = {://000179553200091}, author = {Lanca, M. C. and Dias, C. J. and Dasgupta, D. K. and Marat-Mendes, J.}, editor = {Vieira, T.} }