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Giant electrocaloric effect in ferroelectric poly(vinylidenefluoride-trifluoroethylene) copolymers near a first-order ferroelectric transition
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10.1063/1.4756697
/content/aip/journal/apl/101/13/10.1063/1.4756697
http://aip.metastore.ingenta.com/content/aip/journal/apl/101/13/10.1063/1.4756697
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(a) Schematic of the calorimeter for the ECE measurement. The other face of the heat flux sensor is attached to a large Cu plate (thermal bath) to maintain a constant temperature T. Thin and long silver wires are used for the electric connections (also linked to the thermal bath) to the ECE film and the resistor heater to ensure that the heat exchange of the ECE film and the resistor through the electric wires are orders of magnitude smaller than that from the heat flux sensor. (b) A typical recorded heat flux sensor signal which is from the 20 Mrad irradiated copolymer at 50 °C under a square field of 180 MV/m (5 s duration). The integrated area under the curve is the heat ejected as the field is applied or absorbed when the field is removed. The fact that the signal is zero around time ∼0 when the field is on (at time = −3 s) indicates that the irradiated copolymer has very little Qjoule. (c) The recorded heat flux sensor signal from the normal ferroelectric P(VDF-TrFE) 65/35 copolymer. There is a non-zero reading (indicated by the red hatched region) when the field is on, indicating joule heat. In the QECE and ΔS presented in the paper, Qjoule has been removed.

Image of FIG. 2.
FIG. 2.

Dielectric constant at 1 kHz as a function of temperature for (a) normal ferroelectric P(VDF-TrFE) 65/35 mol. % copolymer and (b) the copolymer irradiated with 20 Mrad of high energy electrons (1.2 MeV energy). Data taken at both heating (filled circles) and cooling scans (filled squares) are presented.

Image of FIG. 3.
FIG. 3.

Directly recorded ECE signal from the flux sensor when the P(VDF-TrFE) 65/35 mol. % films under an uni-polar electric field pulse of 100 MV/m with pulse width larger than 10 s measured at 60 °C, 90 °C, and 100 °C. The positive signals correspond to the heat ejection from the film as the field is applied and the negative signals are when the field is removed. The integrated area corresponds to the heat ejected or heat absorbed.

Image of FIG. 4.
FIG. 4.

ΔSh and ΔSc of 65/35 mol. % copolymer films (a) under 100 MV/m uni-polar field (from the first field cycle at each temperature) as a function of temperature; (b) under 50 MV/m uni-polar field (from the first field cycle at each temperature) as a function of temperature; and (c) under 100 MV/m uni-polar square wave of 0.05 Hz and at 85 °C as a function of field cycle number. The error bar represents the data dispersion of entropy changes in different samples. It should be noted that ΔSh is always larger than ΔSc within the same sample. (d) ΔSh and ΔSc of 20 Mrad irradiated 65/35 mol. % copolymer films under 100 MV/m uni-polar field (from the first field cycle at each temperature) as a function of temperature; (e) under 100 MV/m uni-polar square wave of 0.05 Hz at 50 °C as a function of field cycle number; and (f) at 50 °C under different electric field amplitude. ΔSave (≈ΔSint) as a function of electric field is also presented in (f). At 180 MV/m, ΔSh is 190 J kg−1 K−1 and ΔSint ∼ 160 J kg−1 K−1.

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/content/aip/journal/apl/101/13/10.1063/1.4756697
2012-09-26
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Giant electrocaloric effect in ferroelectric poly(vinylidenefluoride-trifluoroethylene) copolymers near a first-order ferroelectric transition
http://aip.metastore.ingenta.com/content/aip/journal/apl/101/13/10.1063/1.4756697
10.1063/1.4756697
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