Giant pyroelectric effect for energy conversion via tuning lattice compatibility Chenbo Zhang, 1,2 Zhuohui Zeng, 1 Zeyuan Zhu, 1 Nobumichi Tamura, 3 Xian Chen 1* 1 Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong 2 Institute for Advanced Study, Hong Kong University of Science and Technology, Hong Kong 3 Advanced Light Source, Lawrence Berkeley National Laboratory, CA 94720, USA ∗ E-mail: xianchen@ust.hk Abstract Searching for performant pyroelectric materials is gathering research interest for its potential in clean electricity generation and waste heat harvesting. Here we report achieving the giant pyroelectric effect in materials undergoing a first-order phase transformation with high reversibility by tuning the crystallographic compatibility. The single crystalline Ba 0.95 Ca 0.05 Ti 0.99 Zr 0.005 Ce 0.005 O 3 shows a pyroelectric coefficient of 1.93 μC/(cm 2 K), substantially higher than that of most of the state-of- the-art pyroelectric generators by orders of magnitude. We demonstrate that it lights a LED directly without attaching an external power source and consistently generates about 6μA/cm 2 current density by small thermal fluctuations near 100 ◦ C over 540 complete phase transformation cycles with no degradation. This promising material candidate brings pyroelectric energy conversion closer to a practical realization. Electrically polarized crystals naturally exhibit the pyroelectric effect: a change in temperature causes a change in its spontaneous electrical polarization. The earliest documented observation of pyroelectric effect in stones such as tourmaline can date back to ancient Greece. [1] Since the 1960s, pyroelectric materials have attracted profound attention due to their suitability for thermal sensing and thermal imag- ing [2, 3]. Later, some theoretical models were proposed by Olsen, Evans and Drummond to explore the heat-to-electricity conversion as utilizing these materials as the dielectric layer in capacitors, called di- electric power converter (DPC) [4–6]. Their work underlies the thermodynamics of energy conversion by pyroelectric effect. This idea was further optimized and demonstrated in relaxor ferroelectrics. [7, 8] As the nano-fabrication techniques flourished, pyroelectric energy conversion designs based on Olsen cycles have been revitalized in thin film devices. [9–12] One of the obstacles preventing pyroelectric energy conversion from broad commercialization is that the pyroelectric effect is weak in common relaxor thin 1 arXiv:2105.07201v1 [cond-mat.mtrl-sci] 15 May 2021