High Thermoelectric Performance in GeTe-Based Compounds

Development of thermoelectric (TE) materials & devices is important, for energy saving via waste heat power generation [1], and as dynamic power sources for IoT sensors, etc. [2]. We are systematically developing novel principles which can overcome the traditional tradeoffs between the thermoelectric properties, namely to enhance Seebeck coefficient, and selectively lower thermal conductivity, in order to lead to viable high performance TE materials & devices [3 and references therein].<br/>GeTe is an attractive thermoelectric material since it is relatively easy to synthesize and possesses particularly high thermoelectric performance. I will present several of our works and strategies on it. Initially trying to achieve a magnetic enhancement effect, Cr doping was tried in GeTe, and had the serendipitous effect to lower the formation energy of Ge defects. This led to creation of homogenously distributed Ge precipitations and Ge vacancies, coupled with typical band convergence doping to lead to an extremely high figure of merit ZT~2 for a Pb-free material [4]. A high entropy approach of AgInTe2 alloying into GeTe, stabilized the cubic phase, thereby enabling enhanced doping of Bi, leading to the first stable n-type conduction in GeTe [5]. The hidden role of rhombohedral distortion degree on the Ge-vacancy formation energy was revealed and utilized leading to high power factor and average ZT [6]. A combined theoretical and experimental screening of some unusual dopants of GeTe revealed Zr to be an effective dopant [7]. Recently a collaborator work focusing on modifying the charge transfer was able to achieve an exceptional ZT~2.7 [8]. Support from JST Mirai Large-Scale Program (JPMJMI19A1) and collaborators are acknowledged.<br/><i>References </i><br/>[1] L. E. Bell, Science <b>321</b>, 1457 (2008), JOM <b>68</b>, 2673-2679 (2016).<br/>[2] T. Mori, S. Priya, MRS Bulletin <b>43</b>, 176 (2018), I. Petsagkourakis et al, Sci. Tech. Adv. Mater. <b>19</b>, 836 (2018), N. Nandihalli et al., Nano Energy <b>78</b>, 105186 (2020).<br/>[3] T. Mori, Small <b>13</b>, 1702013 (2017), T. Hendricks et al., Energies <b>15</b>, 7307 (2022).<br/>[4] J. Shuai, Y. Sun, X. Tan, and T. Mori, Small <b>16</b>, 1906921 (2020).<br/>[5] Z. Liu, N. Sato, Q. Guo, W. Gao, and T. Mori, NPG Asia Materials <b>12</b>:66 (2020).<br/>[6] Z. Liu, W. Gao, W. Zhang, N. Sato, Q. Guo, and T. Mori, Adv. Energy Mater. <b>10</b>, 2002588 (2020).<br/>[7] B. Srinivasan et al., J. Mater. Chem. A <b>8</b>, 19805 (2020). <i>Selected as F</i><i>ront </i><i>C</i><i>over</i><br/>[8] C. Liu et al., Sci. Adv. <b>9</b>, eadh0713 (2023).