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.