High pressure synthesis and thermoelectric properties of polycrystalline Bi2Se3

- Polycrystalline Bi2Se3 was promptly produced with a high pressure synthesis method.
- Bi2Se3 phases with R3¯m and Pnma symmetry are dominant in the HPS samples produced at 1 GPa and 3 GPa, respectively.
- The Bi2Se3 was densified in a bulk with SPS, which shows an anisotropic texture.
- The highest ZT of 0.37 was achieved in the final bulk along the compressing direction of SPS.

Polycrystalline Bi2Se3 samples were produced with high pressure synthesis. X-ray diffraction measurements indicated that the crystal structure of Bi2Se3 is closely related to the synthetic pressure. While the trigonal phase with R3¯m symmetry was achieved at 1 GPa, the orthorhombic phase with Pnma symmetry was dominant at pressure higher than 3 GPa. This result is consistent with the first-principles calculations. XRD and SEM measurements revealed an anisotropic texture in the R3¯m Bi2Se3 sample densified with spark plasma sintering, which was further demonstrated in the thermoelectric properties. The highest ZT of 0.37 was achieved at 560 K along the compressing direction of spark plasma sintering, a relatively high value for undoped Bi2Se3.