TY - JOUR
T1 - Thermoelectric Properties and Electronic Structures of CuTi 2 S 4 Thiospinel and Its Derivatives
T2 - Structural Design for Spinel-Related Thermoelectric Materials
AU - Hashikuni, Katsuaki
AU - Suekuni, Koichiro
AU - Usui, Hidetomo
AU - Chetty, Raju
AU - Ohta, Michihiro
AU - Kuroki, Kazuhiko
AU - Takabatake, Toshiro
AU - Watanabe, Kosuke
AU - Ohtaki, Michitaka
N1 - Funding Information:
We thank Y. Shibata for the EPMA performed at the Natural Science Center for Basic Research and Development, Hiroshima University, and Atsushi Yamamoto for supporting the electrical and thermal transport measurements at Research Institute for Energy Conservation, AIST. This work was supported financially by JSPS KAKENHI Grant JP17H04951 (to K.S.), grant from the International Joint Research Program for Innovative Energy Technology funded by METI, and CREST JST Grant JPMJCR16Q6.
PY - 2019/1/22
Y1 - 2019/1/22
N2 - We report the preparations, thermoelectric and magnetic properties, and electronic structures of Cu-Ti-S systems, namely, cubic thiospinel c-Cu 1-x Ti 2 S 4 (x ≤ 0.375), a derivative cubic and Ti-rich phase c-Cu 1-x Ti 2.25 S 4 (x = 0.5, 0.625), and a rhombohedral phase r-CuTi 2 S 4 . All samples have the target compositions except for r-CuTi 2 S 4 , whose actual composition is Cu 1.14 Ti 1.80 S 4 . All of the phases have n-type metallic character and exhibit Pauli paramagnetism, as proven by experiments and first-principles calculations. The Cu and Ti deficiencies in c-Cu 1-x Ti 2 S 4 and r-CuTi 2 S 4 , respectively, decrease the electron-carrier concentration, whereas the "excess" of Ti ions in c-Cu 1-x Ti 2.25 S 4 largely increases it. For r-CuTi 2 S 4 , the reduced carrier concentration increases the electrical resistivity and Seebeck coefficient, leading to the highest thermoelectric power factor of 0.5 mW K -2 m -1 at 670 K. For all of the Cu-Ti-S phases, the thermal conductivity at 670 K is 3.5-5 W K -1 m -1 , where the lattice part of the conductivity is as low as 1 W K -1 m -1 at 670 K. As a result, r-CuTi 2 S 4 shows the highest dimensionless thermoelectric figure of merit ZT of 0.2. The present systematic study on the Cu-Ti-S systems provides insights into the structural design of thermoelectric materials based on Cu-M-S (M = transition-metal elements).
AB - We report the preparations, thermoelectric and magnetic properties, and electronic structures of Cu-Ti-S systems, namely, cubic thiospinel c-Cu 1-x Ti 2 S 4 (x ≤ 0.375), a derivative cubic and Ti-rich phase c-Cu 1-x Ti 2.25 S 4 (x = 0.5, 0.625), and a rhombohedral phase r-CuTi 2 S 4 . All samples have the target compositions except for r-CuTi 2 S 4 , whose actual composition is Cu 1.14 Ti 1.80 S 4 . All of the phases have n-type metallic character and exhibit Pauli paramagnetism, as proven by experiments and first-principles calculations. The Cu and Ti deficiencies in c-Cu 1-x Ti 2 S 4 and r-CuTi 2 S 4 , respectively, decrease the electron-carrier concentration, whereas the "excess" of Ti ions in c-Cu 1-x Ti 2.25 S 4 largely increases it. For r-CuTi 2 S 4 , the reduced carrier concentration increases the electrical resistivity and Seebeck coefficient, leading to the highest thermoelectric power factor of 0.5 mW K -2 m -1 at 670 K. For all of the Cu-Ti-S phases, the thermal conductivity at 670 K is 3.5-5 W K -1 m -1 , where the lattice part of the conductivity is as low as 1 W K -1 m -1 at 670 K. As a result, r-CuTi 2 S 4 shows the highest dimensionless thermoelectric figure of merit ZT of 0.2. The present systematic study on the Cu-Ti-S systems provides insights into the structural design of thermoelectric materials based on Cu-M-S (M = transition-metal elements).
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U2 - 10.1021/acs.inorgchem.8b02955
DO - 10.1021/acs.inorgchem.8b02955
M3 - Article
C2 - 30620579
AN - SCOPUS:85059976397
SN - 0020-1669
VL - 58
SP - 1425
EP - 1432
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 2
ER -