Thermoelectric properties of nano-bulk bismuth telluride prepared with spark plasma sintered nano-plates

The pursuit for a high-performance thermoelectric n-type bismuth telluride-based material is significant because n-type materials are inferior to their corresponding p-type materials in highly efficient thermoelectric modules. Herein, to improve the thermoelectric performance of an n-type Bi2Te3, we prepared Bi2Te3 nano-plates with a homogeneous sub-micron size distribution and thickness range of about a few tens of nanometers. This was achieved using a typical nano-chemical synthetic method, and the prepared materials were then spark plasma sintered to fabricate n-type nano-bulk Bi2Te3 samples. We observed a significant enhancement of the anisotropic electrical transport properties for the nano-bulk sample with a higher power factor along the in-plane direction (24.3 μW cm−1 K−2 at 300 K) than that along the out-of-plane direction (8.1 μW cm−1 K−2 at 300 K). However, thermal transport properties were insensitive along the measured direction for the nano-bulk sample. We used a dimensionless figure of merit ZT to calculate the thermoelectric performance. The results showed that the maximum ZT value of 0.69 was achieved along the in-plane direction at 440 K for the nano-bulk n-type Bi2Te3 sample, which was however smaller than that of the previously reported n-type samples (ZT of 1.1). We believe that a further enhancement of the ZT value in the fabricated nano-bulk sample could be accomplished by effectively removing the surface organic ligand of the Bi2Te3 nano-plate particles and optimizing the spark plasma sintering conditions, maintaining the nano-plate morphology intact. •Considerable anisotropic electrical transport properties are observed for the nano-bulk Bi2Te3 material.•The lattice thermal conductivity along the in-plane direction of sample is almost close to that of the corresponding out-of-plane sample.•A maximum ZT of 0.69 are achieved at 440 K for the in-plane sample, which is 68% higher than that of the out-of-plane sample.•A research route toward a facile removal of organic ligands around nano-plates will be promising for a n-type high-performance Bi2Te3 TE material.