Quasi-layered crystal structure coupled with point defects leading to ultralow lattice thermal conductivity in n-type $CU_{2.83}Bi_{10}Se_{16}$

Abstract

$CU_{2.83}Bi_{10}Se_{16}$ a new n-type thermoelectric material, was synthesized via a high-temperature solid-state routine. The quasi-layered structure features of $CU_{2.83}Bi_{10}Se_{16}$ were established by a comprehensive study including variable-temperature single-crystal X-ray diffraction, synchrotron powder X-ray diffraction, DFT calculations, and resonant ultrasound spectroscopy. The structural relationship between $CU_{2.83}Bi_{10}Se_{16}$ and two previously reported compounds, $Cu_{1.6}Bi_{4.8}Se_8$ and $Cu_{1.78}Bi_{4.73}Se_8$, is addressed. The quasi-layered structure of $CU_{2.83}Bi_{10}Se_{16}$ coupled with point defects accounts for its ultralow lattice thermal conductivity. First-principles simulations predict that the electrical properties of $CU_{2.83}Bi_{10}Se_{16}$ are sensitive to Cu content, which is confirmed by the thermoelectric property measurements of $CU_{2.83-x}Bi_{10}Se_{16}$ (x = 0, 0.1, and 0.2) samples. Through tuning the Cu content, $Cu_{2.73}Bi_{10}Se_{16}$ shows the best performance due to the highest Seebeck coefficient combined with a moderate electrical conductivity, achieving zT = 0.42 at 775 K. This work proves that crystal structure engineering can achieve extremely low lattice thermal conductivity in crystalline solids.