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

Abstract 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.