5 research outputs found
Multiple Converged Conduction Bands in K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub>: A Promising Thermoelectric Material with Extremely Low Thermal Conductivity
We
report that K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub> exhibits
multiple conduction bands that lie close in energy and can be activated
through doping, leading to a highly enhanced Seebeck coefficient and
a high power factor with elevated temperature. Meanwhile, the large
unit cell, complex low symmetry crystal structure, and nondirectional
bonding lead to the very low lattice thermal conductivity of K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub>, ranging between 0.42 and 0.20
W m<sup>–1</sup> K<sup>–1</sup> in the temperature interval
300–873 K. Experimentally, we further support the low thermal
conductivity of K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub> using phonon
velocity measurements; the results show a low average phonon velocity
(1605 ms<sup>–1</sup>), small Young’s modulus (37.1
GPa), large Grüneisen parameter (1.71), and low Debye temperature
(154 K). A detailed investigation of the microstructure and defects
was carried out using electron diffraction and transmission microscopy
which reveal the presence of a K<sub>2.5</sub>Bi<sub>8.5</sub>Se<sub>14</sub> minor phase intergrown along the side of the K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub> phase. The combination of enhanced
power factor and low thermal conductivity results in a high <i>ZT</i> value of ∼1.3 at 873 K in electron doped K<sub>2</sub>Bi<sub>8</sub>Se<sub>13</sub> material