We present directly measured electrocaloric effect (ECE) from the P(VDF-TrFE) 65/35 mol% copolymer which displays a first order FE-PE transition. The data reveal that there is a large difference in the ECE between that measured in applying field and in removing the electric field. Near the FE-PE transition, an isothermal entropy change Sh > 190 Jkg-1k-1 is observed when a 100 MV/m electric field is applied. By modifying the copolymer with 20 Mrads of high energy electron irradiation, the difference between the two half-cycles is significantly reduced. At the dielectric peak of 50 oC, the intrinsic Sint becomes 72 J/kgK under 100 MV/m. Under a 180 MV/m, Sint ~ 160 Jkg-1K-1 and an adiabatic temperature change Tint = 35 oC can be induced. The large S observed near the first order FE-PE transition also suggests that there are intermediate states with a large difference in dipolar ordering but a small free energy difference. The mixing of large number of coexisting phases near the first order FE-PE transition leads to the high ECE observed. These results demonstrate the promise of achieving a significant ECE in ferroelectric polymers or ferroelectrics in general by operating near first order FE-PE transition in which multiple intermediate phases can exist.
Citation: Nature Materials
Pub Type: Journals
copolymers, electrocaloric effect, electron irradiation, heat flux sensor, calorimeter