Gigantic Effect due to Phase Transition on Thermoelectric Properties of Ionic Sol–Gel Materials

Sol–gel phase transition in ionic thermoelectrical (i-TE) materials induces large rapid change in viscosity and ionic transport process and is thus expected to yield a drastic variation in thermoelectric properties, crucial in low-grade waste heat harvesting and wearable electronic applications. In this study, four types of i-TE materials are prepared and examined. For the first time, a large rise in the thermopower by 6.5 times during the sol–gel transition of poloxamer/LiCl system is observed, an even greater ionic figure of merit by ≈23 times. The phenomenon is found to be universal as the large variation in thermopower is confirmed in the other transitional materials. The study further reveals the mechanism and proposes a model that deals with the whole process. Finally, six factors influencing the huge variation of the thermopower during the phase-transition are probed and light is shed on the possible gigantic changes of thermopower during the phase transition. A possible route is uncovered to design and control the desired thermoelectric performances of materials, which can lead to a new sight in tunable i-TE devices for low-heat energy harvesting applications.