Lawrence Berkeley National Laboratory

The search for performant multiferroic materials has attracted general research interest in energy science as they have been increasingly exploited as the conversion media among thermal, electric, magnetic, and mechanical energies by using their temperature-dependent ferroic properties. Here we report a material development strategy that guides us to discover a reversible phase-transforming ferroelectric material exhibiting enduring energy harvesting from small temperature differences. The material satisfies the crystallographic compatibility condition between polar and nonpolar phases, which shows only 2.5°C thermal hysteresis and a high figure of merit. It stably generates 15μA of electricity in consecutive thermodynamic cycles in the absence of any bias fields. We demonstrate our device to consistently generate 6μA/cm2 current density near 100°C over 540 complete phase transformation cycles without any electric and functional degradation. The energy-conversion device can light up an LED directly without attaching an external power source. This promising material candidate brings the low-grade waste-heat harvesting closer to a practical realization, e.g., small temperature fluctuations around the water boiling point can be considered as a clean energy source.