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-xGaN 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-xGaN 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 TiO6 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-xGaN ceramics with x = 0.1 wt% driven by a temperature gradient of 2 oC, 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.