Fig. 1: Olsen cycle.
From: Large harvested energy with non-linear pyroelectric modules
a, Sketch of an entropy (S)–temperature (T) diagram with electric field on and off applied to a NLP material exhibiting a phase transition. Two energy harvesting cycles are shown in two different temperature regions. The blue and green cycles occur in and out, respectively, of the phase transition, ending up in very different surface areas. b, Two unipolar DE loops of a 1-mm-thick PST MLC measured between 0 and 155 kV cm−1 at 20 °C and 90 °C, respectively, and the corresponding Olsen cycle. The letters ABCD refer to the different states in the Olsen cycle. A–B: MLC charged up to 155 kV cm−1 at 20 °C. B–C: MLC kept at 155 kV cm−1 while the temperature increases up to 90 °C. C–D: MLC discharged at 90 °C. D–A: MLC cooled down to 20 °C at zero field. The cyan area corresponds to the input electrical energy needed to run the cycle. The orange area is the energy harvested in one cycle. c, Top panel, voltage (black) and current (red) versus time monitored during the same Olsen cycle as in b. The two insets are enlargements of voltage and current at crucial moments in the cycle. In the bottom panel, the yellow and green curves are the corresponding temperature profile and energy, respectively, of the 1-mm-thick MLC. Energy is calculated from the current and voltage curves in the top panel. Negative energy corresponds to harvested energy. The capital letters in the four graphs correspond to the same steps as the Olsen cycle. Cycle AB'CD corresponds to a Stirling cycle (Supplementary Note 7).
