Ultralow thermal conductivity in diamondoid lattices: high thermoelectric performance in chalcopyrite Cu0.8+yAg0.2In1−yTe2

• Published in: Energy & environmental science Vol. 13; no. 10; pp. 3693 - 3705
• Main Authors: Xie, Hongyao, Hao, Shiqiang, Cai, Songting, Bailey, Trevor P, Uher, Ctirad, Wolverton, Christopher, Dravid, Vinayak P, Kanatzidis, Mercouri G
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2020
• Subjects: Absorption spectra; Acoustic velocity; Bonding strength; Carrier density; Carrier mobility; Chalcopyrite; Diamonds; Gruneisen parameter; Heat conductivity; Heat transfer; Lattices; Low temperature; MATERIALS SCIENCE; Mathematical analysis; Phonons; Power factor; Specific heat; Strong interactions (field theory); Thermal conductivity; Thermoelectric materials; Thermoelectricity; Transport properties
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d0ee02323j

Because of its unique transport properties, CuInTe2 has been considered as a promising p-type material for thermoelectric applications. However, its diamondoid structure gives it a high intrinsic lattice thermal conductivity that greatly limits its thermoelectric performance. In this study, we demonstrate that Ag alloying gives rise to an extremely low lattice thermal conductivity of 0.47 W m−1 K−1 for Cu0.8Ag0.2InTe2 at 850 K. Moreover, we found Cu doping significantly improves the carrier mobility while simultaneously increasing the carrier concentration. As a result, the power factor of Cu0.8Ag0.2InTe2 increases and a maximum ZT of ∼1.6 is achieved at 850 K. Both DFT calculations and low temperature heat capacity measurements suggest a strong interaction between low frequency optical phonons and heat carrying acoustic phonons, which is derived from the weak Ag–Te bonding. This strong phonon coupling decreases the Debye temperature and induces a low sound velocity.