Heat-to-Electricity Conversion Using Barium Strontium Titanate Multilayer Capacitors

Pyroelectric materials are attractive for converting heat into electricity, yet the best performance is obtained with lead-containing ceramics, remaining a major environmental concern. Here, we address this problem by developing lead-free barium strontium titanate multilayer capacitors (Ba_0.65Sr_0.35Ti_0.998Mn_0.002O₃ MLCs). A maximum energy density of 3.7 J cm^-3 is achieved under an applied field of 300 kV cm^-1 across a 170 K temperature span in an Olsen electro-thermodynamic cycle. We conducted Olsen cycles with two approaches: electric displacement-electric field (D-E) loops and stepwise control of temperatures and voltages, which provide consistent results. In addition, we found that Ba_0.65Sr_0.35Ti_0.998Mn_0.002O₃ MLCs show a second-order ferroelectric-to-paraelectric (FE-to-PE) phase transition, which shifts to higher temperatures by the applied electric field. This provides a broad and practical temperature window for low-grade waste heat recovery. Our study shows that the performance of pyroelectric energy harvesting in barium strontium titanate materials is comparable to their conventional lead-based counterpart (3.6 J cm^-3 in lead scandium tantalate in similar conditions), revealing the promising prospects of sustainable energy recovery applications.