TY  - JOUR
A1  - Raman Venkatesan, Thulasinath
A1  - Wübbenhorst, Michael
A1  - Gerhard, Reimund
T1  - Structure-property relationships in three-phase relaxor-ferroelectric terpolymers
JF  - Ferroelectrics
N2  - Poly(vinylidenefluoride-trifluoroethylene)-based (P(VDF-TrFE)-based) terpolymers represent a new class of electroactive polymer materials that are relaxor-ferroelectric (RF) polymers and that offer unique and attractive property combinations in comparison with conventional ferroelectric polymers. The RF state is achieved by introducing a fluorine-containing termonomer as a "defect" into the ferroelectric P(VDF-TrFE) copolymer, which reduces the interaction between the VDF/TrFE dipoles. The resulting terpolymer exhibits a low Curie transition temperature and small remanent and coercive fields yielding a slim hysteresis loop that is typical for RF materials. Though the macroscopic behavior is similar to RF ceramics, the mechanisms of relaxor ferroelectricity in semi-crystalline polymers are different and not fully understood yet. Structure-property relationships play an important role in RF terpolymers, as they govern the final RF properties. Hence, a review of important characteristics, previous studies and relevant developments of P(VDF-TrFE)-based terfluoropolymers with either chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) as the termonomer is deemed useful. The role of the termonomer and of its composition, as well as the effects of the processing conditions on the semi-crystalline structure which in turn affects the final RF properties are discussed in detail. In addition, the presence of noteworthy transition(s) in the mid-temperature range and the influence of preparation conditions on those transitions are reviewed. A better understanding of the fundamental aspects affecting the semi-crystalline structures will help to elucidate the nature of RF activity in VDF-based terpolymers and also help to further improve their applications-relevant electroactive properties.
KW  - Relaxor-ferroelectric (RF) fluoropolymers
KW  - structure-property
KW  - relationships
KW  - Curie transition
KW  - dielectric hysteresis
KW  - thermal
KW  - processing
KW  - mid-temperature transition(s)
Y1  - 2022
U6  - https://doi.org/10.1080/00150193.2021.2014260
SN  - 0015-0193
SN  - 1563-5112
VL  - 586
IS  - 1
SP  - 60
EP  - 81
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Raman Venkatesan, Thulasinath
A1  - Gulyakova, Anna A.
A1  - Frübing, Peter
A1  - Gerhard, Reimund
T1  - Relaxation processes and structural transitions in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) relaxor-ferroelectric terpolymers as seen in dielectric spectroscopy
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Dielectric relaxation processes and structural transitions in Poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films with two different monomer compositions were investigated in comparison with Poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer films as reference material. Differential Scanning Calorimetry was employed to assess annealing effects on phase transitions and crystalline structure, while relaxation processes were investigated by means of Dielectric Relaxation Spectroscopy, the results of which indicate the existence of two separate dispersion regions, denoted as processes A and B, respectively. Process A appears at a certain temperature independent of frequency, but is strongly influenced by the crystallisation temperature and the CFE content, while peak B shows typical features of a relaxation process and is less influenced by crystallisation temperature and CFE content. Furthermore, peak B is related to the glass transition which is more pronounced in the terpolymer than in P(VDF-TrFE). A closer analysis indicates that the addition of CFE and thermal annealing gradually shift the ferro-to-paraelectric transition in P(VDF-TrFE) to lower temperatures, while the phase transition is transformed more and more into a relaxation.
KW  - P(VDF-TrFE-CFE) terpolymer
KW  - relaxor-ferroelectric polymer
KW  - dielectric relaxation spectroscopy
KW  - Curie transition
KW  - differential scanning calorimetry
Y1  - 2018
U6  - https://doi.org/10.1109/TDEI.2018.007440
SN  - 1070-9878
SN  - 1558-4135
VL  - 25
IS  - 6
SP  - 2229
EP  - 2235
PB  - Institut of Electrical and Electronics Engineers
CY  - Piscataway
ER  -