Thermoelectric coupling effect in BNT-based pyroelectric ceramics for low-grade temperature driven energy harvesting

Abstract Pyroelectric energy harvesting has received increasing attention in recent years due to its ability to convert low-grade waste heat into electricity for sustainable development. However, the low output energy density driven by low-grade temperature limits its practical applications. Here, we report a high-performance hybrid BNT-BZT- x GaN thermal energy harvesting system with environmentally friendly lead-free BNT-BZT pyroelectric matrix and high thermal conductivity GaN as dopant. The theoretical analysis of BNT-BZT and BNT-BZT- x GaN with x = 0.1 wt% suggests that the introduction of GaN facilitates the resonance vibration between Ga and Ti, O atoms, which not only contributes to the enhancement of the lattice heat conduction, but also improves the vibration of TiO 6 octahedra, resulting in simultaneous improvement of thermal conductivity and pyroelectric coefficient. Therefore, a thermoelectric coupling enhanced energy harvesting density of 80 µJ cm −3 has been achieved in BNT-BZT- x GaN ceramics with x = 0.1 wt% driven by a temperature gradient of 2 o C, at the optical load resistance of 600 MΩ. This theoretical understanding provides a guidance to establish new principles for designing pyroelectric materials with further improved thermal energy harvesting performance.