Intrinsic electrocaloric effects in ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymers: Roles of order of phase transition and stresses

The electrocaloric effects accompanied with the ferroelectric to paraelectric phase transitions in poly(vinylidene fluoride-trifluoroethylene) are investigated within the Landau-Devonshire theory. Just changing the nature of the phase transition from the first-order to the second-order reduces the isothermal entropy change, adiabatic temperature change and refrigerant capacity. The isothermal entropy change in the second-order transition is about one half of that in the first-order one, which is confirmed by experiments and is also consistent with the magnetocaloric counterpart. Converting to be film also leads to the reduction in electrocaloric effects, generally ascribed to the decrease of pyroelectric coefficients. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3353989]