Defect Chemistry of Promising N-Type Thermoelectric Y₂Ti₂O₅S₂

One of the many pathways to decreasing the impact of climate change is to increase the efficiency of current fossil fuel based systems. Even the best internal combustion engines suffer from thermal losses where up to 70% of energy is lost as exhaust heat. These losses can be offset to an extent by thermoelectric devices which convert waste heat into useful electrical energy via the Seebeck effect. The efficiency of thermoelectric materials is typically evaluated using the figure of merit (ZT), with some of the best performing materials reaching ZTs of &gt; 2.[1] However, current state-of-the-art thermoelectric materials contain rare or toxic materials, making them commercially unappealing.<br/><br/>Y₂Ti₂O₅S₂ has been experimentally and computationally studied as a potential battery anode and photocatalyst for water-splitting.[2-4] Our recent work shows the intrinsically n-type Y₂Ti₂O₅S₂ is also a promising high temperature thermoelectric, with ZT exceeding 1 above 850 K at charge carrier concentrations of 10¹⁹–10²⁰ cm^-3.[5] Using hybrid density functional theory we investigate the intrinsic defect chemistry to determine the doping potential. Select n-type extrinsic dopants were considered to establish whether the charge carrier concentrations required for high ZT are indeed achievable.<br/><br/><br/>[1] L. D. Zhao, S. H. Lo, Y. Zhang, H. Sun, G. Tan, C. Uher, C. Wolverton, V. P. Dravid and M. G. Kanatzidis, <i>Nature</i>, 2014, <b>508</b>, 373–377.<br/>[2] K. McColl and F. Corà, <i>J. Mater. Chem. A</i>, 2021, <b>9</b>, 7068–7084.<br/>[3] G. Hyett, O. J. Rutt, Z. A. Gál, S. G. Denis, M. A. Hayward and S. J. Clarke, <i>J. Am. Chem. Soc.</i>, 2004, <b>126</b>, 1980–1991.<br/>[4] Q. Wang, M. Nakabayshi, T. Hisatomi et al., <i>Nat. Mater.</i>, 2019, <b>18</b>, 827-832.<br/>[5] K. Brlec, K. B. Spooner, J. M. Skelton, D. O. Scanlon,<i> in submission</i>. Preprint at 10.26434/chemrxiv-2022-zk09d