Lead-free relaxor-ferroelectric thin films for energy harvesting from low-grade waste-heat

One of the ways to mitigate the world energy crisis is to harvest clean and green energy from waste-heat, which is abundant, ubiquitous, and free. Energy harvesting of this waste-heat is one of the most encouraging methods to capture freely accessible electrical energy. Ferroelectric materials can be used to harvest energy for low power electronic devices, as they exhibit switchable polarization, excellent piezoelectric and pyroelectric properties. The most important characteristic of ferroelectric materials, in the context of energy harvesting, is their ability to generate electric power from a time-dependent temperature change. In this work, we grew highly c-axis oriented heterostructures of BaZr_0.2Ti_0.8O₃ (barium zirconium titanate, BZT)/Ba_0.7Ca_0.3TiO₃ (barium calcium titanate, BCT) on SrRuO₃ (strontium ruthenate, SRO) and deposited on SrTiO₃ (strontium titanate, STO) single crystalline substrate using pulsed laser deposition (PLD) technique. We investigated the structural, electrical, dielectric, and pyroelectric properties of the above-mentioned fabricated heterostructures. The wide range of θ-2θ X-ray diffraction (XRD) patterns only shows (00l) reflection peaks of heterostructures and the substrate which confirmed that the films are highly c-axis oriented. We are also capable to convert the low-grade waste-heat into electrical energy by measuring various temperature-dependent ferroelectric hysteresis loops of our nanostructure films via pyroelectric Ericsson cycles and the structures show an energy conversion density ~ 10,970 kJ/m³ per cycle. These devices exhibit a large pyroelectric current density of ~ 25 mA/m² with 11.8 °C of temperature fluctuation and the corresponding pyroelectric coefficient of 3425 μC/m²K. Our research findings suggest that these lead-free relaxor-ferroelectric heterostructures might be the potential candidates to harvest electrical energy from waste low-grade thermal energy.