Synthesis of High-Density Bulk Tin Monoxide and Its Thermoelectric Properties

Abstract

SnSe exhibits exceptionally high thermoelectric (TE) figure of merit zT mainly due to its ultralow lattice thermal conductivity (κ_lat) [L.-D. Zhao et al.: Nature 508 (2014) 373.]. It is considered that strong lattice anharmonicity caused by the lone pair electrons of Sn²⁺ results in the ultralow κ_lat. Here, we focus on SnO because it has the lone pair electrons of Sn²⁺ like SnSe. Bulk samples of SnO were synthesized by low-temperature high-pressure spark plasma sintering and their TE properties were examined. The present study revealed that SnO exhibits very low κ_lat (1.44 Wm⁻¹K⁻¹ at 573 K) compared with SnO₂ which has no lone pair electrons. The Grüneisen parameter (γ) of SnO was evaluated to be 1.70 and this high γ leads to large lattice anharmonicity and thereby low κ_lat. Even though SnO has low κ_lat, the zT values were significantly low compared with SnSe. The maximum zT value of SnO was 0.00141 at 573 K. Since the main reason of this low zT is its non-optimized carrier concentration, the zT of SnO can be enhanced through the carrier concentration optimization.