Anisotropy thermoelectric and mechanical property of polycrystalline SnSe prepared under different processes

In this work, the polycrystalline SnSe bulk samples were prepared by the spark plasma sintering (SPS) using the SnSe powders, which were synthesized by the hydrothermal reaction (HR) or the melting reaction (MR), respectively. X-ray diffraction (XRD) patterns reveal strong orientation along the [l00] direction for both wafer samples, but there is obvious different micro-morphologies in the powder and the bulk fracture as shown in scanning electron microscopy (SEM) images. The zigzag type texturing characteristic appears in the entire interior of the bulk sample prepared by the process (HR + SPS), while random arrangement occurs in interior of another bulk sample prepared by the process (MR + SPS).The formation mechanism of the zigzag type texturing come mainly from control of initial powders morphology and pressing into pre-pressed blocks by layers. The special zigzag type texturing characteristic improve the thermoelectric properties of samples, and the highest ZT value (~ 0.67) at 773 K were found in the SnSe bulk sample prepared by the process (HR + SPS) in the direction parallel to the pressing axis. The thermoelectric compatibility factor of samples prepared by the process (HR + SPS) are less than 2 at 773 K. The fracture toughness in the plane that vertical or parallel to the pressing direction was calculated to be 4.0 MPam^1/2 and 4.2 MPam^1/2, respectively. The proper thermoelectric compatibility factor and fracture toughness make the SnSe system better application prospect.