Apr 23, 2024
5:00pm - 7:00pm
Flex Hall C, Level 2, Summit
Xinyi He1,Shigeru Kimura1,Takayoshi Katase1,Terumasa Tadano2,Satoru Matsuishi1,Hidenori Hiramatsu1,Hideo Hosono1,Toshio Kamiya1
MDX Research Center for Element Strategy, International Research Frontiers Initiative, Tokyo Institute of Technology1,Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science2
Given the recently increasing energy crisis, there has been a growing focus on thermoelectric technology for converting waste heat energy into electrical power. The energy conversion efficiency (
ZT) of thermoelectric materials, defined as
ZT =
S2σTκ–1, is determined by the key factors: the Seebeck coefficient (
S), the electronic conductivity (
σ), and thermal conductivity (
κ), which includes both electronic (
κele) and lattice (
κLat) contributions. Therefore, high
ZT thermoelectric materials require large
S and high
σ to achieve a high power factor (PF =
S2σ), along with low
κ to create a sizable temperature gradient. To date, high thermoelectric
ZT values has primarily been demonstrated in heavy metal chalcogenides, but the use of toxic elements, such as Pb and Te, is not preferred for widespread practical applications of thermoelectricity. In this study, we propose inverse perovskite-type oxide Ba
3SiO as a novel class of toxic-element-free thermoelectric materials with high
ZT reported so far. First, we experimentally demonstrate that undoped Ba
3SiO bulks exhibit rather high
ZT = 0.16–0.84 at
T = 300–623 K. In addition to these promising experimental results, we demonstrate that the maximum
ZT is estimated to be 2.14 for Ba
3SiO at
T = 600 K when optimally doped, based on the first-principles carrier and phonon transport calculations. The maximum
ZT value of Ba
3SiO is notably higher than those of environmentally benign thermoelectric materials, and it is comparable to those of the high
ZT thermoelectric materials composed of heavy and toxic elements in the same temperature range.
We elucidate the origin of high
ZT for Ba
3SiO and the underlying physical mechanisms through a combination of the experimental analysis and the first-principles calculations. We observed that Ba
3SiO bulks exhibit remarkably low lattice thermal conductivity (
κLat) of 1.00 W/(mK) at
T = 300 K, which is significantly lower than 8.2 W/(mK) of the normal perovskite SrTiO
3 bulk, and even lower than 1.7–2.0 W/(mK) of Bi
2Te
3 and PbTe bulks. The crystal structure of Ba
3SiO is constructed from the highly distorted O–Ba
6 octahedra framework with weak O–Ba ionic bonds, which provides low phonon group velocity and strong phonon scattering. Additionally, Ba
3SiO possesses favorable band structures for achieving a high PF, where the valence band around the Fermi level arises from the
p state of the negatively charged Si anion with large ion size, and their highly dispersive bands with multiple valley degeneracy enable both high
σ and high
S, simultaneously, leading to the high
ZT for Ba
3SiO originating from the low
κLat and the high PF. These results suggest that inverse-perovskite oxides are promising and environmentally benign thermoelectric materials, offering a compelling alternative to current practical materials composed of heavy and toxic elements.