Surface texture of Bi2Te3-based materials deformed under pressure-current heating

Deformation of Bi₂Te₃-based materials was performed. The source disks with nominal compositions of (Bi_0.25Sb_0.75)₂Te₃, (Bi_0.25Sb_0.75)₂(Te_0.95Se_0.05)₃ and (Bi_0.90Sb_0.10)₂(Te_0.95Se_0.05)₃ were cut from the ingots grown by the vertical Bridgman method (VBM). The disks were deformed by either cold press (CP) or pressure current heating (PCH). The crystal structures of the deformed materials were identified to be hexagonal by X-ray diffraction. By using the diffraction intensities, the degree of the preferred orientation was estimated, where the texture of the (00middot l ) plane was detected in the thin surface layer regions of the (PCH) materials. The thermal stress acting to the Bi₂Te₃-based material was estimated by using physical properties at the heterogeneous contact between the graphite and the Bi₂Te₃-based material at PCH temperature. The extension stress was found to be large enough to deform the Bi₂Te₃-based material at the contact surface. Therefore, it can be concluded that the origin of the surface texture is attributed to the thermal stress at the heterogeneous contact. The resistivity measured parallel to the pressing axis was 1/6 less than that measured perpendicular to the axis. However the anisotropies in Seebeck coefficient and carrier concentration were not so clearly detected in these two directions. The power factors of the PCH deformed materials were comparable to those of the original as-grown ingot.