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

SnSe exhibits exceptionally high thermoelectric (TE) figure of merit zT mainly due to its ultralow lattice thermal conductivity (kappa(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 kappa(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 kappa(lat) (1.44 Wm(-1) K-1 at 573 K) compared with SnO2 which has no lone pair electrons. The Gruneisen parameter (gamma) of SnO was evaluated to be 1.70 and this high gamma leads to large lattice anharmonicity and thereby low kappa(lat). Even though SnO has low kappa(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.