TY  - JOUR
A1  - Qiu, Xunlin
A1  - Holländer, Lars
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Basso, Heitor Cury
T1  - Direct hysteresis measurements on ferroelectret films by means of a modified Sawyer-Tower circuit
JF  - Journal of applied physics
N2  - Ferro- and piezo-electrets are non-polar polymer foams or film systems with internally charged cavities. Since their invention more than two decades ago, ferroelectrets have become a welcome addition to the range of piezo-, pyro-, and ferro-electric materials available for device applications. A polarization-versus-electric-field hysteresis is an essential feature of a ferroelectric material and may also be used for determining some of its main properties. Here, a modified Sawyer-Tower circuit and a combination of unipolar and bipolar voltage waveforms are employed to record hysteresis curves on cellular-foam polypropylene ferroelectret films and on tubular-channel fluoroethylenepropylene copolymer ferroelectret film systems. Internal dielectric barrier discharges (DBDs) are required for depositing the internal charges in ferroelectrets. The true amount of charge transferred during the internal DBDs is obtained from voltage measurements on a standard capacitor connected in series with the sample, but with a much larger capacitance than the sample. Another standard capacitor with a much smaller capacitance-which is, however, still considerably larger than the sample capacitance-is also connected in series as a high-voltage divider protecting the electrometer against destructive breakdown. It is shown how the DBDs inside the polymer cavities lead to phenomenological hysteresis curves that cannot be distinguished from the hysteresis loops found on other ferroic materials. The physical mechanisms behind the hysteresis behavior are described and discussed.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4809556
SN  - 0021-8979
VL  - 113
IS  - 22
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Basso, Heitor Cury
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Temporal evolution of the re-breakdown voltage in small gaps from nanoseconds to milliseconds
JF  - Applied physics letters
N2  - A detailed understanding of electric breakdown in dielectrics is of scientific and technological interest. In gaseous dielectrics, a so-called re-breakdown is sometimes observed after extinction of the previous discharge. Although time-dependent re-breakdown voltage is essentially known, its behavior immediately after the previous discharge is not precisely understood. We present an electronic circuit for accurate measurements of the time-dependent re-breakdown voltage in small gaps from tens of nanoseconds to several milliseconds after the previous spark. Results from such experiments are compared with earlier findings, and relevant physical mechanisms such as heating of the gas, decay of the plasma, and ionization of excited atoms and molecules are discussed. It is confirmed that the thermal model is not valid at times below several microseconds.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4773518
SN  - 0003-6951
VL  - 102
IS  - 1
PB  - American Institute of Physics
CY  - Melville
ER  -